What is a 15K square wave?
Pulses of infinitely intense sound pressure changes occurring 30,000 times a second.
It's a sum of multiple sine waves. The 15kHz square wave would have a natural harmonic at 15kHz and a second harmonic at 45kHz at 1/3 the amplitude and a third harmonic at 75kHz at 1/5 the amplitude and so on.
You can't hear any of the harmonics except the natural harmonic at 15kHz. Don't pretend you can. Don't pretend anybody else can. No human has proven in an A/B test that they can hear any frequencies equal to or above 45kHz.
What is a 15K sine wave?
The gentlest possible oscillation of sound pressure, 30,000 times a second.
A single sine wave at 15kHz. You'll hear this.
Now, maybe your tweeters aren't up to putting out infinite sound pressure levels- technically the nature of a square wave is that no matter how faint it is you need to put infinite force into the transients in order to keep it square.
No amplifier would ever pass frequencies above 22kHz to the speakers. High frequencies like this could easily damage crossovers, speakers, etc. It would certainly damage the output stage of the amplifier.
There are, however, plenty of speakers out there that will try a lot harder to render the edges of that 15K square wave. Electrostatics. Fancy tweeters. Horn-loaded designs such as Klipsch uses. I'm currently using very fragile inverted domes with a variation on horn loading; I suggest that my speakers can produce louder sounds in the supersonic range than yours can. Since square waves are made up of transients of theoretically infinite force, it matters whether the speaker is able to produce loud sounds that high up- it translates to ability to make the square wave _be_ a square wave acoustically.
The thing is, we people who know mathematics know that the only frequency in a square wave below 20kHz is the 15kHz sine wave. The nearest frequency to that 15kHz sine wave is at 45kHz.
You claim you can hear this 45kHz harmonic. Either you're hearing distortion (which I'm sure an audiophile would never admit to) or you're full of shit. I'm willing to bet on the latter.
Amusingly, sampling at 44.1K cannot properly capture _either_ because there's an intermodulation distortion that is waaaay beyond what people consider acceptable for total harmonic distortion. Now if you were talking about a 14700 hz note, you'd get a lot closer as that gives you three samples per cycle- either way you are producing a pulse wave at 1/3 width but at least it doesn't warble:)
What a load of techno-babble! You don't know what you're talking about.
If you do the math, you'll see that the maximum error you obtain with 16-bit sampling is all you need given that line-out signals are 3 volts peak-peak. I don't remember the exact voltage, and I'm too tired to re-work it now. (3 volts divided by 2^16...) But the maximum error of a 16-bit sampled signal is FAR lower than the minimum electrical noise added by even the best super-high quality amplifiers with gold-plated speaker wire contacts and the like.
Now while this is entirely true it gets more interesting than this in real-life. There is a need for better than 16-bit resolution. Here's why.
You know that you reconstruct your signal from the samples by using zero-order-hold on each sample, then applying an ideal low-pass filter at half the sampling rate.
Sadly you can't make ideal low-pass filters for any money. In fact it's hard to make even good low-pass filters. The solution is to interpolate the signal first then use a much cheaper and less accurate low-pass filter.
Linear interpolation (first-order-hold) is common but produces nasty results. Bandlimited interpolation (sinc pulses) is a much better method but difficult to implement. In practise you'd use something halfway between the two.
However all interpolation methods rely on the sample being as close to perfect as possible. If you're using first-order-hold then you will only get the error from the nearest two samples. But if you're using bandwidth interpolation then the sinc function means ALL THE SAMPLES are used to create your interpolated sample.
In practise several dozen samples will be combined to create your interpolated sample. The errors from all these samples combine to create one huge error on your interpolated sample.
24-bit samples greatly reduce interpolation errors. 16-bit sampling is only good enough if we have perfect DACs and ideal low-pass filters. 24-bit samples will allow the use of practical DACs and cost-effective low-pass filters.
Wasn't the DVD Audio standard going to move to 24 bit sampling as well?
Yes, and it is a good thing. 16-bit samples are good but not great. 24-bit samples are getting well past the great and into the "more than we'll ever need" stage.
Smaller samples produce quantisation errors. The noise produced by quantisation errors is difficult to remove. 24-bit samples make these errors basically irrelevant.
It's interesting to notice that audiophiles often focus on vinyl's claimed (but untrue) higher recordable frequencies, but neglect the far more important quantisation errors.
CD has quantisation errors approximately 2 orders of magnitude smaller than vinyl (-26db).
Truth is, one of the unfortunate byproducts of digital sampling is something called 'aliasing' of frequencies above fN. Think this: a sound byte is sampled at 44100 Hz. The Nyquist is 22050 Hz. A 21000 Hz sine wave will be reproduced alright, but another 24000 Hz sin wave (22050 + 150 Hz) will show up as 21000 (22050 - 150 Hz) in the digital sample upon playback.
Wrong. It will alias to 24000 - 22050 = 1950Hz.
So when music is digitized, some fancy low-pass filters are required on the input to prevent this aliasing effect.
This is correct. Low-pass filters are used before sampling to prevent aliasing.
Now, one of the problems with filters is that 'perfect' filters are somewhat imposible. Even good low-pass filters which must exhibit near -20dB at fN, roll-off about -3dB at fN-10%.
Also correct.
So the whole point of this is that frequencies near the Nyquist must have already been attenuated or discolorization of frequencies above 12kHz or so will occur.
And suddenly wrong again. You have a source signal x(t) which is comprised of nothing but sine waves. This is Fourier's discovery. You low-pass the signal at 20kHz. You now only have sine waves with frequencies under 20kHz.
The discolouration occurs only above 20kHz. But, we know that most people can't hear those frequencies anyway, and certainly most people's speakers have trouble doing better than -3dB at anything over 18kHz anyway. So it's hardly any loss at all to throw away the sine waves over 20kHz. You Won't Hear Them Anyway.
That's why I swear by good vinyl. A good needle/cartridge and amp can give impressive 30kHz results! Ironically, most people can't really hear this anyway, but most audiophiles will agree it makes for a crisp,full sound that sounds dynamic, as opposed to digital, which sounds cold or flat in comparison. Not that records have the best signal/noise ratio stats;-)
Most audiophiles are full of shit. The weight of a physical needle restricts it's dynamics to well under 18kHz and the granularity of vinyl produces a maximum SNR resolution of 70dB. Laser tracking record players on platinum originals I'll wager would be better than CD, but people who prefer vinyl are fooling themselves.
A square wave of 22050 can NOT be reproduced by even the most ideal audio equipment.
Sure. This is because a square wave at 22050 Hz contains frequencies above 22050 Hz.
A square wave contains a single sine wave at the square wave frequency and many harmonics at integer multiples of that frequency. When you sample a square wave you're actually sampling AN INFINITE number of sine waves. These harmonics are well beyond the ability of your ear to hear.
Now at least some of the harmonics of a square wave will have a frequency higher than half your sampling rate. So if you naively sampled a 22050 Hz square wave at 44100 Hz, of course you would corrupt the signal. This is why a recording studio will low-pass the source before sampling at approximately 22050 Hz. It removes the harmonics you'd never hear anyway.
Close to the Nyquist limit you're basically limited to reproducing sinewaves, however there is no quarantee that the original waveform was a sinewave.
All signals are composed of sine waves. Nyquist says nothing about square waves because a square wave is just a collection of sine waves. The Nyquist theorem lets you reproduce sine waves perfectly up to half the sampling rate. This nonsense about "but I applied a square wave and Nyquist was wrong" is totally stupid. What you've actually done is sampled several sine waves, most of them at frequencies well above half the sampling rate, then found that they got badly aliased.
Saying this is means you're "limited to reproducing sine waves" is just nonsense. There is no other signal except a sine wave. The Nyqust limit is entirely correct.
This is why higher sampling rates (and I mean substantially higher, not lame-ass 96kHz) is important for accurate reproduction of the original signal
For accurate reproduction, yes. But you won't be able to hear that accurate reproduction!
Let's get something straight: when it's said people can hear up to 22kHz tones, that is a sine wave at 22kHz. If you try and listen to a 22kHz square wave then you will ONLY HEAR the first harmonic at 22kHz. All the other harmonics will be beyond your range of hearing.
There is no need to sample higher than 96kHz for audio purposes. There's no real need to sample much higher than 50kHz, despite some of the absolute nonsense that people claim. The standard of sampling at 96kHz is absolute over kill for human ears.
Nyquist's theorem states that the highest frequency that can be represented is one half the sampling rate. This is obvious because you must be able to detect at least a peak and a valley of the sound wave.
Entirely correct.
Nyquist's theorem does not imply, however, that the representation of the maximum [or near maximum] frequencies will be highly accurate as far as the shape of the wave form is concerned. At and around 1/2 sampling freqency, the wave forms become basically nothing but square waves [alternating between a single high, and a single low point]. In order to deal with this, some sound decoders will attempt to interpolate the waves, but they cannot reproduce the original sound accurately. This is why higher sampling frequencies ARE relevent to higher audio fidelity. Higher bit resolutions are arguable though..
You fail! This idea that the signal is not perfectly represented just because you have only two sample points is complete nonsense. Only two sample points are needed because you know the encoded signal must have been low-pass filtered at half the sampling rate before sampling (otherwise you would have introduced aliasing errors). Given this information you can entirely reproduce the original signal as it was before sampling. Nyquist's theorem states that you can exactly reproduce the signal if sampled at twice the signal's maximum frequency. I quote Oppenheim and Willsky:
The sampling theorem establishes the fact that a bandlimited signal is uniquely represented by its samples.
In layman's terms: you don't need more bits to reproduce the original signal. You just need a perfect low-pass filter on your output and infinite precision on your PCM samples. A sine wave with sampling points at the exact peaks and troughs will produce a square wave of the same frequency after sampling/modulation. This square wave will contain the frequency you want plus odd harmonics. The harmonics are naturally going to be higher frequencies and so they will be removed by an appropriately picked low-pass filter. And what's the appropriate cut-off frequency for your low-pass filter? 1/2 the sampling rate, of course. The result is the original sine wave.
Now in practise they actually do sample at higher than the low-pass cut-off frequency, but this is because of other limitations. The PCM samples are only 16-bit, not infinite precision. Also there is no such thing as an ideal low-pass filter: realistic (and affordable) filters will take several kHz to drop from 0dB to -9dB. Also you need exactly -/2 phase difference between your sampling pulse train and the source signal. There are also aliasing issues but at this point the discussion gets heavily into mathematics.
Higher resolution is what is actually needed but this is expensive to achieve. Increasing the sampling rate is far more practical (considering how fast CPUs are) and a heck of a lot cheaper. This is the real reason DVD audio samples at 96kHz. It's not because you can hear 48kHz tones but because it lets the DVD manufacturers use cheap DACs and cheap low-pass filters without sacrificing fidelity.
What nonsense! When the Saturn-5 was launched we weren't sending up dozens of satellites per year. We weren't routinely sending supplies to manned space stations. We weren't routinely doing manned launches to repair broken satellites or correct their decaying orbits.
There are far more "missions into space" now than ever before. This is a huge advance on 30 years ago.
Sure, we can't build a Saturn-5 today. That's mostly a matter of supportive industries. It's the same reason the European beer brewers are having trouble getting trained hoopers. It's the same reason you can't pickup some cheap spare parts for your steam-powered ocean cruiser. It's the same reason that makes electronic valves so rare.
In each case the technology was superceded by something better/cheaper/faster. Wood barrels replaced by aluminium kegs. Steam-powered ocean cruisers by diesel powered cruisers. Electronic valves by transistors. The old technology still exists but only for hobbiests, and occasionally for specific niche applications. It certainly makes the old technology more expensive and far less accessible.
Not being able to build a Saturn-5 isn't a sign of decline. It's a sign that the technology behind the Saturn-5 was made redundant
The players themselves are region-crippled, but the salesman wastes no time in telling you that they offer a professional modification service for a reasonable fee.
This was the case for 2 department stores and 3 hifi stores that I tried. It's almost the first thing out of the salesman's mouth.
And all the local stores have Region-1 displays in addition to their usual Region-4 areas.
Everyone's ignoring the regions. It's costing us money to fix the players, and it's a pain in the arse, but nobody respects it. Especially not the stores or player manufacturers.
My bad. I had Galaxy for six months before cancelling the service. I must have had the wire mesh microwave type because my "dish" (a tiny little thing) was aimed directly at Telstra Tower. I didn't realise there was a second type of Galaxy dish built for satellite reception.
You don't need an actual satellite. You just use satellite dishes. The dishes point at each other. They don't point into the skies. They're all pointing at somebody elses dish nearby.
The Galaxy "satellite" dishes didn't point at a satellite either. They pointed at a local transmission tower (Telstra Tower, or as all the locals call it, Black Mountain Tower).
I know [X is] just a glorified, networkable display driver.
People such as yourself have launched on huge "let's throw away X" projects before. All such projects inevitably stumble and fall after the core developers realise there's far more to a windowing system than just "networkable display drivers".
Rather than attack X you should identify the faults in X and fix them. If you have definite proof that the X architecture is so flawed that it can't be saved, you should publish a paper and educate all those idiots working on XFree86 so they don't waste any further time.
Or perhaps it's possible that the people who work on XFree86 know more about this topic than you do.
Don't they have the right to control the product they produce?
If they sell the product to you, or present it to you as a gift, then no they have no rights to control your use of it whatsoever. This is pretty much the entire point.
The fact that they've tried to control the use is why people are upset. And it's not just some childish need to "pull it apart". This is a basic human right. It's something you should fight for. Instead you've rolled over and given it away.
I'm surprised you could even being to believe that a corporation has the right to control your life. What a disgusting thought. It reeks of the very things people have spent thousands of years fighting against.
I dread the day when apathy and ignorance has spread so far that corporations can get away with actions such as these. People such as yourself are speeding up the process, and it scares the almighty crap out of me.
You think Motorhead isn't "too commercial"? And since when has Black Flag been hardcore!
I'm personally sick of the trendy "Metallica is not a real metal band" nonsense. They're always either "too commercial" or "not hardcore" or "a bunch of sellouts". What crap.
You don't have to like Metallica, but don't use the copout excuse that it's because they're too wussy for you. Metallica is entertaining: their popularity is a direct result of this.
Strangely enough the text doesn't talk about cost-efficiency ratings for gas powered plants. It has some details on how they work in the technical section, but the cost analysis section concentrates mostly on renewable sources as opposed to nuclear/coal/oil (the most common power plants). The textbook has a very definite bias towards encouraging renewable sources, though it does a fair job of pointing out the flaws in many of the existing renewable sources.
The textbook is also very much an overview rather than a detailed study of the market forces and technical reasons behind real life deployment of power plants. This means the arguments it makes could possibly be flawed because of their simplicity. Coal power plants have one amazing benefit over every other form of power plant: people know how to build them and companies are tooled to produce the necessary parts. One of the highest costs in setting up renewable energy source power plants is the cost of tooling. The book only briefly mentions this but I think it's a very strong argument explaining why dirty coal and oil plants are still so common.
OK, so storing one thousand barrels of nuclear waste in your backyard is bad. I agree.
The alternative is to store millions of barrels of sulfuric acid enriched waste from coal and oil plants. That combined with millions of tonnes of ash belched into the air. And the lakes used for cooling heated up by 10s of kelvin, causing environmental damage by killing algae and fish and plant life.
Nuclear waste is bad. No dispute. But people don't realise how bad the fossil fuel pollutants are. I think people should go see a tailings dam, see the dead stunted trees as far as the eye can see, smell the terrible stench of sulfur, and see the dying sick animals that have unluckily wandered into the area.
And even given how bad the power plants are, they are positively sparkling clean when compared to the pollutants produced by your SUV or sports car. Not an individual effort of course, but as combined across the entire country. The power plant is incredibly clean when compared to the millions upon millions of cars, each belching their own toxic mix of monoxides, lead laden gasses, and various nth-ene pollutants. These chemicals are already known to be linked to brain damage in newborns, cancer in adults, and respiratory or lung damage for everyone.
Oil and coal are disgusting fuel sources. Any of the alternatives, even nuclear power, would be preferable.
Nuclear power is unfortunately expensive. It looks damn cheap on paper (1c/kWh vs coal at 4c/kWh) and this encourages people to develop nuclear plants. Also the waste products from nuclear, though extremely toxic, are in such small quantities that it's like 0% emmissions when compared to coal or oil.
But the cost of disposal, due mostly to govt regulations and whining greenies, drives the actual cost of nuclear power up to 7c/kWh, or depending on the country even higher. So it's nearly double the cost of coal power, and it receives so much negative public attention that nuclear fission power is simply not feasible anyway. Nobody wants a nuclear power plant in Australia at all, despite the vast amounts of barren useless land Australia has to offer.
I'm personally peeved at greenies for being anti-nuclear. Sure, they can be catastrophic, so when they do pollute they do it in a big way. But compared to the destruction of the environment due to oil/coal, nuclear is nothing. Millions of acres of land are destroyed for coal mines alone but nuke out a few thousand acres of land in the middle of the poverty stricken former USSR and suddenly nuclear power is off limits. It seems to me sometimes people can't see the alternatives to nuclear power are far worse. It's not like anyone builds those dangerous carbon core style reactors anymore. The modern nuclear reactor is far safer.
But even given that, nuclear is not cheap. You're better off with wind power. There's nothing wrong with fois de gras anyway.
Your figures for electric motors (90%) and combustion engines (19%) are 100% in agreement with the textbook I've got here. But the 70-80% power plant efficiency seems way off.
Old style oil fired plants never exceeded 40% efficiency. This textbook talks about a modern (fairly revolutionary) design by Siemens that gets 65% efficiency.
Power plants are still 2 to 3 times better than small "personal" engines, but they're not 4 to 5 times better as you're suggesting here.
I agree that hybrid engines seem to be the next best evolutionary step. They require very little change to the infrastructure (you can still "fill it up") while almost doubling efficiency and halving the emissions. The fully electric car seems to have captured the public's attention though.
Your claims are rife with inaccuracies and misleading statements. Look at just a few of the real doozies.
Electric cars use upto 5 times as much fossil fuels than ICE (internal combustion engine) vehicles.
Modern oil-fired and coal-fired plants are getting 35-40% efficiency ratings. This compares wonderfully with the 25% efficiency of petrol engines or 30% efficiency of diesel engines. Even with ridiculously inefficient transmission, storage, and final conversion, electric cars are still more efficient in terms of quantity of fuel used. An ICE also produces far more toxic emissions due to not having the benefits of high-quality scrubbers and catalytic convertors (though you did comment on the reduced quantity of emissions, you didn't mention that the gasses produced by ICE are thousands of times more toxic to plant and animal life than power plant emissions).
Secondly, the efficiency of first generating the electricity from fossil fuels to drive a motor by electricity, rather than via an ICE is much, much lower.
This is just an outright lie. Even factoring in ridiculously high transmission losses from plant to car (say 40%), and even given a highly inefficient electric motor (say 75%), an entirely electrically powered car is still going to be more efficient and result in fewer emissions to the air. The quality of air produced by fossil fuel plants is amazingly good compared to an ICE so there's simply no comparison here.
And if you are even thinking of solar power, don't bother. Solar cells would have to be 25 times as efficient as they exist now. Putting solar panels atop...
Solar Power Plants don't ever rely on solar photovoltaic cells or panels. Not only are they far too expensive, the cells "wear out" after only 10 years usage. Modern solar plants use the tried and true heliocentric model. Mirrors or chromed surfaces reflect large areas of sunlight into a single point (either a tower with a collection point at the top, or using new trough technology with a copper pipe running down the centre of the reflective trough). These plants are in operation RIGHT NOW in Australia, and are turning 6c/kWh which is very favourable compared to the 4c/kWh of coal (currently the cheapest source of electricity).
I also see no mention of true, realistic, and even commercially viable zero-emission plants. They do exist but your rant seems to imply every person pushing for zero emissions is living in fantasy land and none of this is possible. Let's take a look at some of the zero emission plants in operation right now.
Hot-rock power is a new finding in a joint Australian-American investigation. You send water pipes 2km into the crust then use the temperature difference between surface and bedrock to drive a steam turbine. Estimates are that a single 2km cube of rock in the Australian desert could power the entire of Australia's power needs. Still in the experimental stage.
Wind power, currently the best bet for future zero-emission plants. Currently pushing 5c/kWh which is better value even than nuclear. It's in the running for beating oil/coal plants in the near future. People are concerned about the ugly nature of wind farms, but these same people never seem to complain about open-cut mines or tailings dams or the unsightly fossil fuel power plants.
Dam power, such as found in the hydro-electric power plants in Australia. Uses the natural water cycle (evaporation, condensation, water flow) to produce vast amounts of power. These plants have no emissions, are very cheap to maintain, and the high construction costs are easily offset by the long running lifetime.
And there is the fact that the current power generation infrastructure could not meet the power generation needs to support home charging of electrical cars if 1/4th of America was driven them.
This argument is ridiculous. By the same token nobody should ever have built modems, because at one stage there weren't enough ISPs to dial into. Power plants take a while to build (the typical estimate is 10 years per plant) but electric cars won't magically appear overnight. They'll slowly phase in alongside normal cars and power plants can be built to meet demand. The people who build and run the plants already know how to figure in rising demand: they've been doing it for decades.
I agree electric cars aren't a magical panacea but there's no reason to be a cynic just because they aren't 100% perfect. Electric powered vehicles are an incremental evolutionary improvement. Crying "I won't consider anything that isn't 100% emission free and costs nothing to run and has all the infrastructure already in place" is the attitude the oil barons want you to have.
Sure, but you've missed the point. I'd agree the OS itself is irrelevant where rendering is concerned. I'm sure it could be done on MS-DOS if you wanted to. But that's still not the point.
The point is that Linux is becoming something that is useful to everyone. Not just for UNIX geeks. Not just for trying out UNIX at home, because you can't afford a Sparc.
The shared development over the Internet towards Linux has produced something useful for entirely new groups of people. This is the point. This is the wonderful thing.
Linux doesn't need 100% marketshare to win. Linux wins everytime someone new downloads Linux and says "I like this".
Putting video _drivers_ in kernel mode is not evil. Unfortunately, it is something that linus itself did not want (See the GGI flamefest) so video drivers have been implemented in X. This is evil too. X should not need to run as root.
Now this is an interesting point. Putting the video drivers into the kernel (ala GGI/KGI) is a stability gain, but it unfortunately reduces the overall performance.
The reason why is obvious. Not only do you still have the overhead of user space context switches between X clients and the X server, you now also have a kernel context switch for every syscall that the X server makes to the kernel driver. Previously the X server ran as root so it could just diddle on the hardware.
And there's another problem. Modern video cards are not simple framebuffers. They have all sorts of 2D accelerated operations built into their high speed GPUs. In many cases these GPUs are extremely sensitive to the commands you send: it is trivial to lockup a GPU so it won't receive further commands. So you have two choices:
User space acceleration library with shared locks amongst all clients to coordinate access.
Kernel space acceleration library which then abstracts the acceleration features.
The first method is slower than just putting the acceleration features into the X server and running the X server as root. The second method is what Linus is deathly afraid of: hundreds of video card drivers, each with 10-20kilobytes of acceleration code, all very specific to a video card series, each one of them API incompatible with all the other video card drivers.
Now a good solution is fbcon. The kernel does know enough to initialise the video card and change video modes but refuses to deal with acceleration features. This way it can handle all virtual console changes, even between graphics and non-graphics consoles. This ensures the fbcon driver is small. You also avoid all the common lockups. The X server then lets the kernel handle mode switches, but the X server takes over the GPU and bangs on it like crazy.
It is unlikely GGI/KGI will ever be officially adopted. The fbcon drivers do 99% of what people wanted but with 1% of the code and complexity. It is a difficult problem on UNIX because of the distinction between user/kernel space and because of memory protection between applications. Lesser platforms can cheat and get faster results. To solve this problem neatly on UNIX is hard, and it is taking time, but Linux/XFree86 are slowly but surely getting there.
Quite often because the specs released to XFree86 are incomplete. An example would be the NVIDIA 2D driver. The official NVIDIA 2D driver uses DMA and AGP and is 80% faster than the XFree86 NVIDIA 2D driver which doesn't use DMA or AGP.
There are some cards where XFree86 has been given full specifications and so the 2D and 3D speed is faster than the corresponding Windows driver. I'm not kidding. Check out the Matrox cards.
Also don't mistake Microsoft. They have some of the world's most talented coders and they work on this fulltime. I wouldn't be surprised if their rasteriser is light years ahead of everyone elses.
The networking code between the X client and the X server in XFree86 is a UNIX domain socket. This is possibly the fastest IPC method in Linux. The UNIX domain socket requires only one redundant copy and Linus Torvalds himself has optimised the all mighty crap out of it.
Experts in XFree86 have already tried using other transports to see if things improve. This has in the past included a shared memory segment between the clients and the server. The surprise result was a reduction in speed. It seems that Linux has such a good implementation of UNIX domain sockets that doing it all by hand is an overall loss.
Removing the transport altogether is impossible. This is not an X consideration. No matter what windowing system you have, at one stage you need to pass messages between the clients and the X server, because they are not the same binary and they do not run in the same address space.
So ignore the pipe. The pipe isn't the problem. A real problem is context switching. Because the X server and the X client both run as user space processes the kernel must alternate the execution between client and server. This increases the latency of operations and time is wasted doing the context switching.
One solution that can result in a speedup is to put the X server into kernel space. This saves you one redundant copy and two redundant context switches. It also means your system is now as stable as Microsoft Windows.
The compromise solution is to put some highly timing critical code into the kernel but keep most of it in user space where it belongs. This is the technique that the DRI has used. It means the client can render directly to the hardware while still maintaining a balance between security and stability and clean design.
SUMMARY: The real performance killer of X is not the pipe. Changing the transport has already been tried and has already failed.
Yes, there really were 10 complete versions before X11. There haven't been significant changes to the core since X11 Release 1, so the major version hasn't changed in a while. The changes have mostly been in the extensions (eg, XPrint is the big change for R6.5.1).
Slashdot Mirror
It's a sum of multiple sine waves. The 15kHz square wave would have a natural harmonic at 15kHz and a second harmonic at 45kHz at 1/3 the amplitude and a third harmonic at 75kHz at 1/5 the amplitude and so on.
You can't hear any of the harmonics except the natural harmonic at 15kHz. Don't pretend you can. Don't pretend anybody else can. No human has proven in an A/B test that they can hear any frequencies equal to or above 45kHz.
A single sine wave at 15kHz. You'll hear this.
No amplifier would ever pass frequencies above 22kHz to the speakers. High frequencies like this could easily damage crossovers, speakers, etc. It would certainly damage the output stage of the amplifier.
The thing is, we people who know mathematics know that the only frequency in a square wave below 20kHz is the 15kHz sine wave. The nearest frequency to that 15kHz sine wave is at 45kHz.
You claim you can hear this 45kHz harmonic. Either you're hearing distortion (which I'm sure an audiophile would never admit to) or you're full of shit. I'm willing to bet on the latter.
What a load of techno-babble! You don't know what you're talking about.
Now while this is entirely true it gets more interesting than this in real-life. There is a need for better than 16-bit resolution. Here's why.
You know that you reconstruct your signal from the samples by using zero-order-hold on each sample, then applying an ideal low-pass filter at half the sampling rate.
Sadly you can't make ideal low-pass filters for any money. In fact it's hard to make even good low-pass filters. The solution is to interpolate the signal first then use a much cheaper and less accurate low-pass filter.
Linear interpolation (first-order-hold) is common but produces nasty results. Bandlimited interpolation (sinc pulses) is a much better method but difficult to implement. In practise you'd use something halfway between the two.
However all interpolation methods rely on the sample being as close to perfect as possible. If you're using first-order-hold then you will only get the error from the nearest two samples. But if you're using bandwidth interpolation then the sinc function means ALL THE SAMPLES are used to create your interpolated sample.
In practise several dozen samples will be combined to create your interpolated sample. The errors from all these samples combine to create one huge error on your interpolated sample.
24-bit samples greatly reduce interpolation errors. 16-bit sampling is only good enough if we have perfect DACs and ideal low-pass filters. 24-bit samples will allow the use of practical DACs and cost-effective low-pass filters.
Yes, and it is a good thing. 16-bit samples are good but not great. 24-bit samples are getting well past the great and into the "more than we'll ever need" stage.
Smaller samples produce quantisation errors. The noise produced by quantisation errors is difficult to remove. 24-bit samples make these errors basically irrelevant.
It's interesting to notice that audiophiles often focus on vinyl's claimed (but untrue) higher recordable frequencies, but neglect the far more important quantisation errors.
CD has quantisation errors approximately 2 orders of magnitude smaller than vinyl (-26db).
Wrong. It will alias to 24000 - 22050 = 1950Hz.
This is correct. Low-pass filters are used before sampling to prevent aliasing.
Also correct.
And suddenly wrong again. You have a source signal x(t) which is comprised of nothing but sine waves. This is Fourier's discovery. You low-pass the signal at 20kHz. You now only have sine waves with frequencies under 20kHz.
The discolouration occurs only above 20kHz. But, we know that most people can't hear those frequencies anyway, and certainly most people's speakers have trouble doing better than -3dB at anything over 18kHz anyway. So it's hardly any loss at all to throw away the sine waves over 20kHz. You Won't Hear Them Anyway.
Most audiophiles are full of shit. The weight of a physical needle restricts it's dynamics to well under 18kHz and the granularity of vinyl produces a maximum SNR resolution of 70dB. Laser tracking record players on platinum originals I'll wager would be better than CD, but people who prefer vinyl are fooling themselves.
No, the previous poster is entirely correct.
Sure. This is because a square wave at 22050 Hz contains frequencies above 22050 Hz.
A square wave contains a single sine wave at the square wave frequency and many harmonics at integer multiples of that frequency. When you sample a square wave you're actually sampling AN INFINITE number of sine waves. These harmonics are well beyond the ability of your ear to hear.
Now at least some of the harmonics of a square wave will have a frequency higher than half your sampling rate. So if you naively sampled a 22050 Hz square wave at 44100 Hz, of course you would corrupt the signal. This is why a recording studio will low-pass the source before sampling at approximately 22050 Hz. It removes the harmonics you'd never hear anyway.
All signals are composed of sine waves. Nyquist says nothing about square waves because a square wave is just a collection of sine waves. The Nyquist theorem lets you reproduce sine waves perfectly up to half the sampling rate. This nonsense about "but I applied a square wave and Nyquist was wrong" is totally stupid. What you've actually done is sampled several sine waves, most of them at frequencies well above half the sampling rate, then found that they got badly aliased.
Saying this is means you're "limited to reproducing sine waves" is just nonsense. There is no other signal except a sine wave. The Nyqust limit is entirely correct.
For accurate reproduction, yes. But you won't be able to hear that accurate reproduction!
Let's get something straight: when it's said people can hear up to 22kHz tones, that is a sine wave at 22kHz. If you try and listen to a 22kHz square wave then you will ONLY HEAR the first harmonic at 22kHz. All the other harmonics will be beyond your range of hearing.
There is no need to sample higher than 96kHz for audio purposes. There's no real need to sample much higher than 50kHz, despite some of the absolute nonsense that people claim. The standard of sampling at 96kHz is absolute over kill for human ears.
Entirely correct.
You fail! This idea that the signal is not perfectly represented just because you have only two sample points is complete nonsense. Only two sample points are needed because you know the encoded signal must have been low-pass filtered at half the sampling rate before sampling (otherwise you would have introduced aliasing errors). Given this information you can entirely reproduce the original signal as it was before sampling. Nyquist's theorem states that you can exactly reproduce the signal if sampled at twice the signal's maximum frequency. I quote Oppenheim and Willsky:
In layman's terms: you don't need more bits to reproduce the original signal. You just need a perfect low-pass filter on your output and infinite precision on your PCM samples. A sine wave with sampling points at the exact peaks and troughs will produce a square wave of the same frequency after sampling/modulation. This square wave will contain the frequency you want plus odd harmonics. The harmonics are naturally going to be higher frequencies and so they will be removed by an appropriately picked low-pass filter. And what's the appropriate cut-off frequency for your low-pass filter? 1/2 the sampling rate, of course. The result is the original sine wave.
Now in practise they actually do sample at higher than the low-pass cut-off frequency, but this is because of other limitations. The PCM samples are only 16-bit, not infinite precision. Also there is no such thing as an ideal low-pass filter: realistic (and affordable) filters will take several kHz to drop from 0dB to -9dB. Also you need exactly -/2 phase difference between your sampling pulse train and the source signal. There are also aliasing issues but at this point the discussion gets heavily into mathematics.
Higher resolution is what is actually needed but this is expensive to achieve. Increasing the sampling rate is far more practical (considering how fast CPUs are) and a heck of a lot cheaper. This is the real reason DVD audio samples at 96kHz. It's not because you can hear 48kHz tones but because it lets the DVD manufacturers use cheap DACs and cheap low-pass filters without sacrificing fidelity.
What nonsense! When the Saturn-5 was launched we weren't sending up dozens of satellites per year. We weren't routinely sending supplies to manned space stations. We weren't routinely doing manned launches to repair broken satellites or correct their decaying orbits.
There are far more "missions into space" now than ever before. This is a huge advance on 30 years ago.
Sure, we can't build a Saturn-5 today. That's mostly a matter of supportive industries. It's the same reason the European beer brewers are having trouble getting trained hoopers. It's the same reason you can't pickup some cheap spare parts for your steam-powered ocean cruiser. It's the same reason that makes electronic valves so rare.
In each case the technology was superceded by something better/cheaper/faster. Wood barrels replaced by aluminium kegs. Steam-powered ocean cruisers by diesel powered cruisers. Electronic valves by transistors. The old technology still exists but only for hobbiests, and occasionally for specific niche applications. It certainly makes the old technology more expensive and far less accessible.
Not being able to build a Saturn-5 isn't a sign of decline. It's a sign that the technology behind the Saturn-5 was made redundant
Same in Australia.
The players themselves are region-crippled, but the salesman wastes no time in telling you that they offer a professional modification service for a reasonable fee.
This was the case for 2 department stores and 3 hifi stores that I tried. It's almost the first thing out of the salesman's mouth.
And all the local stores have Region-1 displays in addition to their usual Region-4 areas.
Everyone's ignoring the regions. It's costing us money to fix the players, and it's a pain in the arse, but nobody respects it. Especially not the stores or player manufacturers.
My bad. I had Galaxy for six months before cancelling the service. I must have had the wire mesh microwave type because my "dish" (a tiny little thing) was aimed directly at Telstra Tower. I didn't realise there was a second type of Galaxy dish built for satellite reception.
You don't need an actual satellite. You just use satellite dishes. The dishes point at each other. They don't point into the skies. They're all pointing at somebody elses dish nearby.
The Galaxy "satellite" dishes didn't point at a satellite either. They pointed at a local transmission tower (Telstra Tower, or as all the locals call it, Black Mountain Tower).
What violation?
Copyright violation? No, because nobody even bothered to copy the lousy Windows software that came with the scanner.
Patent violation? No, because there are no patents here. Or at least if there are then DC hasn't bothered to mention them yet.
Lease violation? No, because there was never any lease involved. The things were sent out for free via mail. They are legally gifts.
IP violation? Perhaps, but this isn't clear cut and certainly you weren't thinking this way (you compared against a coypright, the GPL).
There is no hypocrisy here. That you think there is does little more than demonstrate your woeful ignorance of what's going on.
People such as yourself have launched on huge "let's throw away X" projects before. All such projects inevitably stumble and fall after the core developers realise there's far more to a windowing system than just "networkable display drivers".
Rather than attack X you should identify the faults in X and fix them. If you have definite proof that the X architecture is so flawed that it can't be saved, you should publish a paper and educate all those idiots working on XFree86 so they don't waste any further time.
Or perhaps it's possible that the people who work on XFree86 know more about this topic than you do.
If they sell the product to you, or present it to you as a gift, then no they have no rights to control your use of it whatsoever. This is pretty much the entire point.
The fact that they've tried to control the use is why people are upset. And it's not just some childish need to "pull it apart". This is a basic human right. It's something you should fight for. Instead you've rolled over and given it away.
I'm surprised you could even being to believe that a corporation has the right to control your life. What a disgusting thought. It reeks of the very things people have spent thousands of years fighting against.
I dread the day when apathy and ignorance has spread so far that corporations can get away with actions such as these. People such as yourself are speeding up the process, and it scares the almighty crap out of me.
"This is a DEAD dachshund. It is DECEASED. KAPUT. Gone to dachshund heaven. If it hadn't been nailed to the kennel it would have fallen off."
You think Motorhead isn't "too commercial"? And since when has Black Flag been hardcore!
I'm personally sick of the trendy "Metallica is not a real metal band" nonsense. They're always either "too commercial" or "not hardcore" or "a bunch of sellouts". What crap.
You don't have to like Metallica, but don't use the copout excuse that it's because they're too wussy for you. Metallica is entertaining: their popularity is a direct result of this.
Strangely enough the text doesn't talk about cost-efficiency ratings for gas powered plants. It has some details on how they work in the technical section, but the cost analysis section concentrates mostly on renewable sources as opposed to nuclear/coal/oil (the most common power plants). The textbook has a very definite bias towards encouraging renewable sources, though it does a fair job of pointing out the flaws in many of the existing renewable sources.
The textbook is also very much an overview rather than a detailed study of the market forces and technical reasons behind real life deployment of power plants. This means the arguments it makes could possibly be flawed because of their simplicity. Coal power plants have one amazing benefit over every other form of power plant: people know how to build them and companies are tooled to produce the necessary parts. One of the highest costs in setting up renewable energy source power plants is the cost of tooling. The book only briefly mentions this but I think it's a very strong argument explaining why dirty coal and oil plants are still so common.
OK, so storing one thousand barrels of nuclear waste in your backyard is bad. I agree.
The alternative is to store millions of barrels of sulfuric acid enriched waste from coal and oil plants. That combined with millions of tonnes of ash belched into the air. And the lakes used for cooling heated up by 10s of kelvin, causing environmental damage by killing algae and fish and plant life.
Nuclear waste is bad. No dispute. But people don't realise how bad the fossil fuel pollutants are. I think people should go see a tailings dam, see the dead stunted trees as far as the eye can see, smell the terrible stench of sulfur, and see the dying sick animals that have unluckily wandered into the area.
And even given how bad the power plants are, they are positively sparkling clean when compared to the pollutants produced by your SUV or sports car. Not an individual effort of course, but as combined across the entire country. The power plant is incredibly clean when compared to the millions upon millions of cars, each belching their own toxic mix of monoxides, lead laden gasses, and various nth-ene pollutants. These chemicals are already known to be linked to brain damage in newborns, cancer in adults, and respiratory or lung damage for everyone.
Oil and coal are disgusting fuel sources. Any of the alternatives, even nuclear power, would be preferable.
Nuclear power is unfortunately expensive. It looks damn cheap on paper (1c/kWh vs coal at 4c/kWh) and this encourages people to develop nuclear plants. Also the waste products from nuclear, though extremely toxic, are in such small quantities that it's like 0% emmissions when compared to coal or oil.
But the cost of disposal, due mostly to govt regulations and whining greenies, drives the actual cost of nuclear power up to 7c/kWh, or depending on the country even higher. So it's nearly double the cost of coal power, and it receives so much negative public attention that nuclear fission power is simply not feasible anyway. Nobody wants a nuclear power plant in Australia at all, despite the vast amounts of barren useless land Australia has to offer.
I'm personally peeved at greenies for being anti-nuclear. Sure, they can be catastrophic, so when they do pollute they do it in a big way. But compared to the destruction of the environment due to oil/coal, nuclear is nothing. Millions of acres of land are destroyed for coal mines alone but nuke out a few thousand acres of land in the middle of the poverty stricken former USSR and suddenly nuclear power is off limits. It seems to me sometimes people can't see the alternatives to nuclear power are far worse. It's not like anyone builds those dangerous carbon core style reactors anymore. The modern nuclear reactor is far safer.
But even given that, nuclear is not cheap. You're better off with wind power. There's nothing wrong with fois de gras anyway.
Your figures for electric motors (90%) and combustion engines (19%) are 100% in agreement with the textbook I've got here. But the 70-80% power plant efficiency seems way off.
Old style oil fired plants never exceeded 40% efficiency. This textbook talks about a modern (fairly revolutionary) design by Siemens that gets 65% efficiency.
Power plants are still 2 to 3 times better than small "personal" engines, but they're not 4 to 5 times better as you're suggesting here.
I agree that hybrid engines seem to be the next best evolutionary step. They require very little change to the infrastructure (you can still "fill it up") while almost doubling efficiency and halving the emissions. The fully electric car seems to have captured the public's attention though.
Your claims are rife with inaccuracies and misleading statements. Look at just a few of the real doozies.
Modern oil-fired and coal-fired plants are getting 35-40% efficiency ratings. This compares wonderfully with the 25% efficiency of petrol engines or 30% efficiency of diesel engines. Even with ridiculously inefficient transmission, storage, and final conversion, electric cars are still more efficient in terms of quantity of fuel used. An ICE also produces far more toxic emissions due to not having the benefits of high-quality scrubbers and catalytic convertors (though you did comment on the reduced quantity of emissions, you didn't mention that the gasses produced by ICE are thousands of times more toxic to plant and animal life than power plant emissions).
This is just an outright lie. Even factoring in ridiculously high transmission losses from plant to car (say 40%), and even given a highly inefficient electric motor (say 75%), an entirely electrically powered car is still going to be more efficient and result in fewer emissions to the air. The quality of air produced by fossil fuel plants is amazingly good compared to an ICE so there's simply no comparison here.
Solar Power Plants don't ever rely on solar photovoltaic cells or panels. Not only are they far too expensive, the cells "wear out" after only 10 years usage. Modern solar plants use the tried and true heliocentric model. Mirrors or chromed surfaces reflect large areas of sunlight into a single point (either a tower with a collection point at the top, or using new trough technology with a copper pipe running down the centre of the reflective trough). These plants are in operation RIGHT NOW in Australia, and are turning 6c/kWh which is very favourable compared to the 4c/kWh of coal (currently the cheapest source of electricity).
I also see no mention of true, realistic, and even commercially viable zero-emission plants. They do exist but your rant seems to imply every person pushing for zero emissions is living in fantasy land and none of this is possible. Let's take a look at some of the zero emission plants in operation right now.
Hot-rock power is a new finding in a joint Australian-American investigation. You send water pipes 2km into the crust then use the temperature difference between surface and bedrock to drive a steam turbine. Estimates are that a single 2km cube of rock in the Australian desert could power the entire of Australia's power needs. Still in the experimental stage.
Wind power, currently the best bet for future zero-emission plants. Currently pushing 5c/kWh which is better value even than nuclear. It's in the running for beating oil/coal plants in the near future. People are concerned about the ugly nature of wind farms, but these same people never seem to complain about open-cut mines or tailings dams or the unsightly fossil fuel power plants.
Dam power, such as found in the hydro-electric power plants in Australia. Uses the natural water cycle (evaporation, condensation, water flow) to produce vast amounts of power. These plants have no emissions, are very cheap to maintain, and the high construction costs are easily offset by the long running lifetime.
This argument is ridiculous. By the same token nobody should ever have built modems, because at one stage there weren't enough ISPs to dial into. Power plants take a while to build (the typical estimate is 10 years per plant) but electric cars won't magically appear overnight. They'll slowly phase in alongside normal cars and power plants can be built to meet demand. The people who build and run the plants already know how to figure in rising demand: they've been doing it for decades.
I agree electric cars aren't a magical panacea but there's no reason to be a cynic just because they aren't 100% perfect. Electric powered vehicles are an incremental evolutionary improvement. Crying "I won't consider anything that isn't 100% emission free and costs nothing to run and has all the infrastructure already in place" is the attitude the oil barons want you to have.
Sure, but you've missed the point. I'd agree the OS itself is irrelevant where rendering is concerned. I'm sure it could be done on MS-DOS if you wanted to. But that's still not the point.
The point is that Linux is becoming something that is useful to everyone. Not just for UNIX geeks. Not just for trying out UNIX at home, because you can't afford a Sparc.
The shared development over the Internet towards Linux has produced something useful for entirely new groups of people. This is the point. This is the wonderful thing.
Linux doesn't need 100% marketshare to win. Linux wins everytime someone new downloads Linux and says "I like this".
Now this is an interesting point. Putting the video drivers into the kernel (ala GGI/KGI) is a stability gain, but it unfortunately reduces the overall performance.
The reason why is obvious. Not only do you still have the overhead of user space context switches between X clients and the X server, you now also have a kernel context switch for every syscall that the X server makes to the kernel driver. Previously the X server ran as root so it could just diddle on the hardware.
And there's another problem. Modern video cards are not simple framebuffers. They have all sorts of 2D accelerated operations built into their high speed GPUs. In many cases these GPUs are extremely sensitive to the commands you send: it is trivial to lockup a GPU so it won't receive further commands. So you have two choices:
The first method is slower than just putting the acceleration features into the X server and running the X server as root. The second method is what Linus is deathly afraid of: hundreds of video card drivers, each with 10-20kilobytes of acceleration code, all very specific to a video card series, each one of them API incompatible with all the other video card drivers.
Now a good solution is fbcon. The kernel does know enough to initialise the video card and change video modes but refuses to deal with acceleration features. This way it can handle all virtual console changes, even between graphics and non-graphics consoles. This ensures the fbcon driver is small. You also avoid all the common lockups. The X server then lets the kernel handle mode switches, but the X server takes over the GPU and bangs on it like crazy.
It is unlikely GGI/KGI will ever be officially adopted. The fbcon drivers do 99% of what people wanted but with 1% of the code and complexity. It is a difficult problem on UNIX because of the distinction between user/kernel space and because of memory protection between applications. Lesser platforms can cheat and get faster results. To solve this problem neatly on UNIX is hard, and it is taking time, but Linux/XFree86 are slowly but surely getting there.
Quite often because the specs released to XFree86 are incomplete. An example would be the NVIDIA 2D driver. The official NVIDIA 2D driver uses DMA and AGP and is 80% faster than the XFree86 NVIDIA 2D driver which doesn't use DMA or AGP.
There are some cards where XFree86 has been given full specifications and so the 2D and 3D speed is faster than the corresponding Windows driver. I'm not kidding. Check out the Matrox cards.
Also don't mistake Microsoft. They have some of the world's most talented coders and they work on this fulltime. I wouldn't be surprised if their rasteriser is light years ahead of everyone elses.
The networking code between the X client and the X server in XFree86 is a UNIX domain socket. This is possibly the fastest IPC method in Linux. The UNIX domain socket requires only one redundant copy and Linus Torvalds himself has optimised the all mighty crap out of it.
Experts in XFree86 have already tried using other transports to see if things improve. This has in the past included a shared memory segment between the clients and the server. The surprise result was a reduction in speed. It seems that Linux has such a good implementation of UNIX domain sockets that doing it all by hand is an overall loss.
Removing the transport altogether is impossible. This is not an X consideration. No matter what windowing system you have, at one stage you need to pass messages between the clients and the X server, because they are not the same binary and they do not run in the same address space.
So ignore the pipe. The pipe isn't the problem. A real problem is context switching. Because the X server and the X client both run as user space processes the kernel must alternate the execution between client and server. This increases the latency of operations and time is wasted doing the context switching.
One solution that can result in a speedup is to put the X server into kernel space. This saves you one redundant copy and two redundant context switches. It also means your system is now as stable as Microsoft Windows.
The compromise solution is to put some highly timing critical code into the kernel but keep most of it in user space where it belongs. This is the technique that the DRI has used. It means the client can render directly to the hardware while still maintaining a balance between security and stability and clean design.
SUMMARY: The real performance killer of X is not the pipe. Changing the transport has already been tried and has already failed.
Yes, there really were 10 complete versions before X11. There haven't been significant changes to the core since X11 Release 1, so the major version hasn't changed in a while. The changes have mostly been in the extensions (eg, XPrint is the big change for R6.5.1).