Even worse than 8 track: Reel to reel. Definitely not a quick process to change tracks, but it did have decent sound quality.
Bit of a catch-all term, that. There were consumer decks which could be pretty crappy, but remember that even long into the CD era, the songs were recorded in the studio on reel-to-reel tape. On a deck that cost as much as a house, and at high speeds on expensive tape, sure... but still reel-to-reel. The first digital recorders were reel-to-reel as well.
More bandwidth is definitely a big thing - MIDI runs at around 31 Kbit/sec and it's fairly easy to swamp it, especially if you're chaining instruments on a single bus.
Increasing the resolution is Really Big Thing. MIDI is 7-bit, which means that if you do something like sweeping a cutoff filter, you only have 127 possible values which gives you very noticeable stepping artifacts (often called 'zipper noise'). Some manufacturers try to interpolate in software. Others bond two controller streams together so that you get 14-bit precision, or send custom NRPM values but since there are a number of incompatible ways of doing this, you have to have a controller keyboard which works the same way as your synthesizer. Setting out an actually standardised way of doing this would be really handy.
Don't know why they still kling to the old DIN-port, USB(-c) was the way to go for MIDI 2.0, backwardcompatibility would be done through USB to DIN (which already exist and work perfectly).
Firstly, MIDI is opto-isolated. Without that, you get weird ground-loop effects like the data leaking into the audio, which happens quite a bit when using USB MIDI.
Secondly, MIDI is peer-to-peer whereas USB has a host and a guest. You cannot plug a USB MIDI keyboard into a USB sound module and expect it to work, you have to have a computer somewhere to act as a broker. With MIDI you can take two cables and link three machines together. USB1.1 doesn't work that way, and that's what the USB-DIN adapters are all using. USB-C might be better in that regard, I'm not sure.
You've also got a very large installed base (probably millions of machines) which are using DIN and USB1.1, switching to USB-C isn't going to. They bent over backwards to ensure that MIDI 2.0 is going to work with your $10000 OB-X with Kenton board.
If a song is less than 29 minutes and 37 seconds (which takes up one and a third sides of a record) then it's not worth listening to. Or at the very least, coding to as I am now (although to be totally accurate, I'm waiting for a build to finish).
Three Minutes, thirty seconds? Bah! Poseurs.
To be fair, Karn Evil Nine is really three tracks welded together. It is certainly good for a coding marathon, though...
These people have money and must hate kids deeper than I can imagine for the time and effort being put into it.
I would expect at least some of it was created by bored teenagers. Back when I was a member of that demographic I put far too much effort into taking things aimed at younger kids and twisting them into something that would today be called 'edgy' for the amusement of myself and my friends. Henry's Cat exhorting people to join an Irish terror group, Honey Monster from Sugar Puffs being turned into a mafia don, editing a Mah-Jongg christmas tile set so the three kings were assassinating baby Jesus in the crib and so forth.
It being the early 90s I had no internet access, and the alterations were done crudely with scissors and marker pen (or the Mah-jongg tile editor). Given the kind of content creation software available now, I can easily imagine some of this stuff being created by a 13-year old with pirated software and too much time on their hands.
"Gone into administration" means that a third party has been appointed to oversee the emergency rescue/shutdown of the company. I'm not sure how that's less intuitive than saying "Gone into chapter 7"...
Another one, pellicles (what's a pellicle?) They aren't ready for prime time. There is exactly one company, ASML, making all the EUV equipment and they are currently burning the midnight oil trying to develop usable pellicles. As I understand it, they currently aren't quite transparent enough (88% minimum required vs 83% current maximum achieved) or durable enough, by about a factor of three. Without pellicles, nobody is making any chips with EUV, and nobody is getting past 7nm.
I believe it's a protective layer over the photomask. I remember reading, last time the EUV thing came up, that TSMC were considering running without using one at all, and taking the hit that they'd need to replace the mask frequently. That might have been just for initial runs or something, I don't really know.
Hint: you have to be able to produce thin plastic ribbons (5.6 micrometres thick for LTO-7 and LTO-8) that are close to a kilometre long. They need to be 12.65mm (plus or minus.006 mm) wide. You then need to bind barium ferrite particles to those ribbons, in a uniform pattern, to be able to hold 6,656 (LTO-8) tracks in that width, with a linear density of 20,668 bits in every mm (per track).
True, but you only really need to worry about coating, slitting and polishing. My understanding from audio tape is that you usually buy in the backing from Dupont or someone. It's still not a trivial process, but it's not impossible either.
Not as easy as your think. The startup cost would be enormous. Very few engineers know, in detail, about thin film technology, it's kinda a lost art. just ask Kodak . The equipment would have to be custom made, no one has manufactured them in decades and the old one have long since been hauled off to the scrap yard.
ATR Magnetics actually did this. They had their own coating machinery made. That's studio recording tape, though, so the tolerances will probably be a lot lower than for ultra-high density digital media on extremely thin backing.
It's the only way for change to happen. Imagine in people from 200 years ago were still alive and voting. We'd never progress as a society.
"And that is as it should be, because death is very likely the single best invention of life. It is life's change agent. It clears out the old to make way for the new."
It also causes valuable lessons to be lost.The people who experienced Hiroshima and it's after-effects are better placed to fight against it happening again than people who just read about it as bored schoolchildren. It becomes easier to deny the holocaust when the survivors are dead of old age. And regulations put in place after the Great Depression were swept away by later generations who considered them obsolete relics, until the consequences became apparent in 2008.
From the late 1940s to about 2005, Ampex DID "do shit", they WERE undeniably relevant, as every utterance and every image that was recorded on magnetic tape from that SIX DECADE time period owes its very existence to the pioneering research spearheaded and financed by singer Bing Crosby and perfected by the scientists at Ampex; but unfortunately for them, recording tape has all but been replaced by other forms of storage media. But if you were more than 12 years old, you'd understand why people believe that their contribution to technological history deserves to be remembered.
Not only that, not only the vast legacy of classic songs recorded on 406 and 456 tape, but computers used tape as backing store until the 80s. Digital audio was only viable because of their videotape systems - it was the only medium we had with enough capacity and bandwidth to make it work. And while we have since moved on to better things, none of this would have happened without the intermediate step that Ampex made possible.
I rather doubt we'd have an internet to discuss and argue on without Ampex.
These new tape decks are 1/4 inch, which are really not made for studio recording, no matter what their looks try to portray.
It's perhaps worth pointing out that 2-track 1/4" at 15ips was the format everything was mixed to until around the mid-80s. 1/2" stereo was sometimes used, and DAT started to become more common in the 1990s, but 1/4" was what all the classic 60s and 70s albums were recorded to.
Unless the album has since been digitally remixed from the multitrack tapes, 1/4" stereo is what the CD or 24/96 digital master will have been created from.
"We know how to do anything digitally and with analogue technology."
Uh, yea, about that; go find me an analog pitch shifter. Good luck with that!
Well, obviously the varispeed control on the tape deck will do that. But if you want to change the pitch without affecting the length of the audio, you need one of these: http://www.wendycarlos.com/oth...
I wonder how difficult it would be to manufacture tape heads again? It wasn't trivial engineering to get the performance we got out of these things before they became obsolete.
There are people who still make them, largely as aftermarket support for studio recorders. JRF Magnetics for one, and I think there's a place in Japan though I forget the name. Besides, cassette decks are still in limited production, and mag stripe readers use similar technology, so it's not like it's entirely lost.
If you used a 1/4 inch tape for a two track recording system (0.125 inch per track), wouldn't that actually be better than using a 2 inch tape for a 24 track recording system (0.0833 inch per track)? I should think the width is important for capturing differences in amplitude, but even more than that, the speed of the tape under the head right? Surely there is an analogue here with the sampling rate issues in digital recording.
It was a compromise between sound quality and track count. In the very late 60s and early 70s, the standard was 2" 16-track which had the same width as the 1/4" stereo master. Running at 30ips, this was basically the pinnacle of studio recording quality on tape and did not require noise reduction. 'Crime of the Century' by Supertramp was done this way and was used as a reference recording for sound systems for at least a decade afterwards.
24-track allowed the artists more flexibility, but the quality went down a little and noise reduction started to become a bit more necessary, though you could still live without if need be. There were more experimental formats such as the Stephens 2" 40-track system which is rumoured to have been used on things like Bohemian Rhapsody where they needed crazy track counts. There were also 32-track machines like some of the Otari MX80s, and I think Telefunken made one too, but the format was a bit too noisy, and by then people were locking multiple 24-track machines together anyway, before finally going over to digital.
Are there many(any) studios that record primarily, in analog?
Do many of them have analog components to them...ie tube amps, pre-amps, tape....etc?
You have to look, but there are, yes. Most big studios have the capability to do things all-analogue but these days it's mostly done as hybrid. I managed to build my own as a hobby because I thought it might be interesting to experience the workflow, and the machines were very cheap on ebay about 10 years back. I could almost certainly get better results by recording everything end-to-end digital, but working on tape is more fun.
The real "magic" tape decks of the 50's - 90's were the ones that ran two-inch tape at 15 inches / second. And that was super expensive. I think $200 for ten minutes is the last I heard, and I think that was for Squirrel Nut Zipper's "Hot"
250 GBP will buy you 2400 feet of 2" tape. Running at 15ips that'll give you about 33 minutes, minus any test tones you may want to record. If you run at 30 you'll get less tape hiss, but you'll also reduce the running time to about 16 minutes, which at current tape prices is crazy. I'm running an Otari MX80 as a (very expensive) hobby and by planning carefully I can usually get an album onto two reels.
The machines being offered here could potentially be used as a 1/4" mixdown deck, but you'd have to be very rich to consider it given that you can get an actual studio recorder off ebay for considerably less.
Recording on 2-inch analog 24-track is different than digital. Tape exhibits saturation effects -- if I record a drum track onto tape, I can record it "hot" by turning up the gain so that the hardest hits saturate the tape. The result is a distinctive compression/limiting/harmonic effect. One of the reasons that people complained about sterile and thin digital sound when we shifted from analog to digital was that digital recorders don't behave the same way.
Another thing is that the frequency response is nonlinear. Jack Endino has some rather interesting graphs of this in different models of 2" deck: http://www.endino.com/graphs/
I had never heard of any of these before and I suspect most other people haven't either, so I don't think they will be missed.
Blackfin I've heard of, but don't know what it is. Tile is the instruction set used by Tilera's parallel CPU, which had 64 cores on a chip about 10 years ago. Looks like they switched the thing over to use ARM cores after the first couple of generations.
Larger dynamic range, I'm sure. Stupid dumbed down writing.
Yes, but not necessarily the way you're thinking.
With vinyl, it tends to be a compromise between volume and running time. That is, if you need more bass or a louder signal, it requires wider grooves which take more space. If you need to cut a single long track, e.g. "The Great Nothing" which is about 27 minutes long, you have to reduce the amplitude to shrink the grooves enough for it to fit.
The business about it being 30% longer and 30% louder is probably a misunderstanding - I would assume it's actually "30% longer OR 30% louder" but that message got garbled somewhere along the line.
Quality/Quantity improvements aside, I'm more excited by the idea that they've skipped all the steps of cutting and electroplating to get the stamper. That could make it a lot cheaper to get records pressed, and that would be a worthwhile breakthrough for independent bands who want their own vinyl.
Or.. now hear me out on this one... or... we could just, you know, send the digitally converted audio, you know, without converting it back into a bumpy piece of plastic.
What you're saying boils down to "You shouldn't make records." That's not the point, and TBH it seems to be needlessly pissing on other people's hobbies, both people who collect vinyl and bands who want a physical copy of their album for posterity.
What a lot of people seem to be missing is that there is already a market for producing vinyl. So much so that new cutting shops and pressing plants are coming online. If these people can skip most of the expensive steps of getting a stamper cut, that will make it easier and cheaper for bands to produce vinyl, and as someone who's paid to have one of their albums pressed, that would be a welcome change.
To increase the amount of playing time, you can vary the width of the grooves depending on the volume and frequency content (louder and more bassy parts need wider grooves), kind of like RLE coding in a way. To do this while cutting the master, you need to know what's going to happen in the next rotation of the disk.
This means you need two signals going into the cutting amplifier, one with the future signal, and one with the signal you're actually cutting to disk. Originally this was achieved using a modified tape deck with an extra playback head stuck way outside of the normal tape path. From the late 70s onwards, they used digital delays. The live signal (off tape, or a WAV file these days) is fed in as the 'future' signal, and the recorded signal is digitally delayed by 1.8 seconds or whatever it was.
There are a few places that still have the modified tape decks for real purists who want a 100% analogue signal chain, or at a pinch you can disable the variable pitch cutting, and have all the grooves exactly the same width as was done in the 50s and earlier, but you only get about 15 minutes per side.
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Even worse than 8 track: Reel to reel. Definitely not a quick process to change tracks, but it did have decent sound quality.
Bit of a catch-all term, that. There were consumer decks which could be pretty crappy, but remember that even long into the CD era, the songs were recorded in the studio on reel-to-reel tape. On a deck that cost as much as a house, and at high speeds on expensive tape, sure... but still reel-to-reel. The first digital recorders were reel-to-reel as well.
More bandwidth is definitely a big thing - MIDI runs at around 31 Kbit/sec and it's fairly easy to swamp it, especially if you're chaining instruments on a single bus.
Increasing the resolution is Really Big Thing. MIDI is 7-bit, which means that if you do something like sweeping a cutoff filter, you only have 127 possible values which gives you very noticeable stepping artifacts (often called 'zipper noise'). Some manufacturers try to interpolate in software. Others bond two controller streams together so that you get 14-bit precision, or send custom NRPM values but since there are a number of incompatible ways of doing this, you have to have a controller keyboard which works the same way as your synthesizer. Setting out an actually standardised way of doing this would be really handy.
Don't know why they still kling to the old DIN-port, USB(-c) was the way to go for MIDI 2.0, backwardcompatibility would be done through USB to DIN (which already exist and work perfectly).
Firstly, MIDI is opto-isolated. Without that, you get weird ground-loop effects like the data leaking into the audio, which happens quite a bit when using USB MIDI.
Secondly, MIDI is peer-to-peer whereas USB has a host and a guest. You cannot plug a USB MIDI keyboard into a USB sound module and expect it to work, you have to have a computer somewhere to act as a broker. With MIDI you can take two cables and link three machines together. USB1.1 doesn't work that way, and that's what the USB-DIN adapters are all using. USB-C might be better in that regard, I'm not sure.
You've also got a very large installed base (probably millions of machines) which are using DIN and USB1.1, switching to USB-C isn't going to. They bent over backwards to ensure that MIDI 2.0 is going to work with your $10000 OB-X with Kenton board.
If a song is less than 29 minutes and 37 seconds (which takes up one and a third sides of a record) then it's not worth listening to. Or at the very least, coding to as I am now (although to be totally accurate, I'm waiting for a build to finish).
Three Minutes, thirty seconds? Bah! Poseurs.
To be fair, Karn Evil Nine is really three tracks welded together. It is certainly good for a coding marathon, though...
These people have money and must hate kids deeper than I can imagine for the time and effort being put into it.
I would expect at least some of it was created by bored teenagers. Back when I was a member of that demographic I put far too much effort into taking things aimed at younger kids and twisting them into something that would today be called 'edgy' for the amusement of myself and my friends. Henry's Cat exhorting people to join an Irish terror group, Honey Monster from Sugar Puffs being turned into a mafia don, editing a Mah-Jongg christmas tile set so the three kings were assassinating baby Jesus in the crib and so forth.
It being the early 90s I had no internet access, and the alterations were done crudely with scissors and marker pen (or the Mah-jongg tile editor). Given the kind of content creation software available now, I can easily imagine some of this stuff being created by a 13-year old with pirated software and too much time on their hands.
"Gone into administration" means that a third party has been appointed to oversee the emergency rescue/shutdown of the company. I'm not sure how that's less intuitive than saying "Gone into chapter 7"...
Another one, pellicles (what's a pellicle?) They aren't ready for prime time. There is exactly one company, ASML, making all the EUV equipment and they are currently burning the midnight oil trying to develop usable pellicles. As I understand it, they currently aren't quite transparent enough (88% minimum required vs 83% current maximum achieved) or durable enough, by about a factor of three. Without pellicles, nobody is making any chips with EUV, and nobody is getting past 7nm.
I believe it's a protective layer over the photomask. I remember reading, last time the EUV thing came up, that TSMC were considering running without using one at all, and taking the hit that they'd need to replace the mask frequently. That might have been just for initial runs or something, I don't really know.
Go ahead. Let us know how it goes.
Hint: you have to be able to produce thin plastic ribbons (5.6 micrometres thick for LTO-7 and LTO-8) that are close to a kilometre long. They need to be 12.65mm (plus or minus .006 mm) wide. You then need to bind barium ferrite particles to those ribbons, in a uniform pattern, to be able to hold 6,656 (LTO-8) tracks in that width, with a linear density of 20,668 bits in every mm (per track).
True, but you only really need to worry about coating, slitting and polishing. My understanding from audio tape is that you usually buy in the backing from Dupont or someone. It's still not a trivial process, but it's not impossible either.
Not as easy as your think. The startup cost would be enormous. Very few engineers know, in detail, about thin film technology, it's kinda a lost art. just ask Kodak . The equipment would have to be custom made, no one has manufactured them in decades and the old one have long since been hauled off to the scrap yard.
ATR Magnetics actually did this. They had their own coating machinery made. That's studio recording tape, though, so the tolerances will probably be a lot lower than for ultra-high density digital media on extremely thin backing.
It's the only way for change to happen. Imagine in people from 200 years ago were still alive and voting. We'd never progress as a society.
"And that is as it should be, because death is very likely the single best invention of life. It is life's change agent. It clears out the old to make way for the new."
It also causes valuable lessons to be lost.The people who experienced Hiroshima and it's after-effects are better placed to fight against it happening again than people who just read about it as bored schoolchildren. It becomes easier to deny the holocaust when the survivors are dead of old age. And regulations put in place after the Great Depression were swept away by later generations who considered them obsolete relics, until the consequences became apparent in 2008.
From the late 1940s to about 2005, Ampex DID "do shit", they WERE undeniably relevant, as every utterance and every image that was recorded on magnetic tape from that SIX DECADE time period owes its very existence to the pioneering research spearheaded and financed by singer Bing Crosby and perfected by the scientists at Ampex; but unfortunately for them, recording tape has all but been replaced by other forms of storage media. But if you were more than 12 years old, you'd understand why people believe that their contribution to technological history deserves to be remembered.
Not only that, not only the vast legacy of classic songs recorded on 406 and 456 tape, but computers used tape as backing store until the 80s. Digital audio was only viable because of their videotape systems - it was the only medium we had with enough capacity and bandwidth to make it work. And while we have since moved on to better things, none of this would have happened without the intermediate step that Ampex made possible.
I rather doubt we'd have an internet to discuss and argue on without Ampex.
These new tape decks are 1/4 inch, which are really not made for studio recording, no matter what their looks try to portray.
It's perhaps worth pointing out that 2-track 1/4" at 15ips was the format everything was mixed to until around the mid-80s. 1/2" stereo was sometimes used, and DAT started to become more common in the 1990s, but 1/4" was what all the classic 60s and 70s albums were recorded to.
Unless the album has since been digitally remixed from the multitrack tapes, 1/4" stereo is what the CD or 24/96 digital master will have been created from.
Biggest question is the availability of audio tape.
I don't know any company making good audio tape, if any audio tape at all.
ATR magnetics and RTM (was Pyral). This is studio-grade stuff mind, so it's not cheap.
"We know how to do anything digitally and with analogue technology."
Uh, yea, about that; go find me an analog pitch shifter. Good luck with that!
Well, obviously the varispeed control on the tape deck will do that. But if you want to change the pitch without affecting the length of the audio, you need one of these: http://www.wendycarlos.com/oth...
I wonder how difficult it would be to manufacture tape heads again? It wasn't trivial engineering to get the performance we got out of these things before they became obsolete.
There are people who still make them, largely as aftermarket support for studio recorders. JRF Magnetics for one, and I think there's a place in Japan though I forget the name. Besides, cassette decks are still in limited production, and mag stripe readers use similar technology, so it's not like it's entirely lost.
If you used a 1/4 inch tape for a two track recording system (0.125 inch per track), wouldn't that actually be better than using a 2 inch tape for a 24 track recording system (0.0833 inch per track)? I should think the width is important for capturing differences in amplitude, but even more than that, the speed of the tape under the head right? Surely there is an analogue here with the sampling rate issues in digital recording.
It was a compromise between sound quality and track count. In the very late 60s and early 70s, the standard was 2" 16-track which had the same width as the 1/4" stereo master. Running at 30ips, this was basically the pinnacle of studio recording quality on tape and did not require noise reduction. 'Crime of the Century' by Supertramp was done this way and was used as a reference recording for sound systems for at least a decade afterwards.
24-track allowed the artists more flexibility, but the quality went down a little and noise reduction started to become a bit more necessary, though you could still live without if need be. There were more experimental formats such as the Stephens 2" 40-track system which is rumoured to have been used on things like Bohemian Rhapsody where they needed crazy track counts. There were also 32-track machines like some of the Otari MX80s, and I think Telefunken made one too, but the format was a bit too noisy, and by then people were locking multiple 24-track machines together anyway, before finally going over to digital.
Are there many(any) studios that record primarily, in analog?
Do many of them have analog components to them...ie tube amps, pre-amps, tape....etc?
You have to look, but there are, yes. Most big studios have the capability to do things all-analogue but these days it's mostly done as hybrid. I managed to build my own as a hobby because I thought it might be interesting to experience the workflow, and the machines were very cheap on ebay about 10 years back. I could almost certainly get better results by recording everything end-to-end digital, but working on tape is more fun.
The real "magic" tape decks of the 50's - 90's were the ones that ran two-inch tape at 15 inches / second. And that was super expensive. I think $200 for ten minutes is the last I heard, and I think that was for Squirrel Nut Zipper's "Hot"
250 GBP will buy you 2400 feet of 2" tape. Running at 15ips that'll give you about 33 minutes, minus any test tones you may want to record. If you run at 30 you'll get less tape hiss, but you'll also reduce the running time to about 16 minutes, which at current tape prices is crazy. I'm running an Otari MX80 as a (very expensive) hobby and by planning carefully I can usually get an album onto two reels.
The machines being offered here could potentially be used as a 1/4" mixdown deck, but you'd have to be very rich to consider it given that you can get an actual studio recorder off ebay for considerably less.
Recording on 2-inch analog 24-track is different than digital. Tape exhibits saturation effects -- if I record a drum track onto tape, I can record it "hot" by turning up the gain so that the hardest hits saturate the tape. The result is a distinctive compression/limiting/harmonic effect. One of the reasons that people complained about sterile and thin digital sound when we shifted from analog to digital was that digital recorders don't behave the same way.
Another thing is that the frequency response is nonlinear. Jack Endino has some rather interesting graphs of this in different models of 2" deck: http://www.endino.com/graphs/
Keep in mind that stock price is based on some weird gut feeling of how a company might perform in future, not on current profitability.
I had never heard of any of these before and I suspect most other people haven't either, so I don't think they will be missed.
Blackfin I've heard of, but don't know what it is. Tile is the instruction set used by Tilera's parallel CPU, which had 64 cores on a chip about 10 years ago. Looks like they switched the thing over to use ARM cores after the first couple of generations.
half speed masters ?
Sounds more like Direct Metal Mastering, but done far more cheaply.
Larger dynamic range, I'm sure. Stupid dumbed down writing.
Yes, but not necessarily the way you're thinking.
With vinyl, it tends to be a compromise between volume and running time. That is, if you need more bass or a louder signal, it requires wider grooves which take more space. If you need to cut a single long track, e.g. "The Great Nothing" which is about 27 minutes long, you have to reduce the amplitude to shrink the grooves enough for it to fit.
The business about it being 30% longer and 30% louder is probably a misunderstanding - I would assume it's actually "30% longer OR 30% louder" but that message got garbled somewhere along the line.
Quality/Quantity improvements aside, I'm more excited by the idea that they've skipped all the steps of cutting and electroplating to get the stamper. That could make it a lot cheaper to get records pressed, and that would be a worthwhile breakthrough for independent bands who want their own vinyl.
Or.. now hear me out on this one... or ... we could just, you know, send the digitally converted audio, you know, without converting it back into a bumpy piece of plastic.
What you're saying boils down to "You shouldn't make records." That's not the point, and TBH it seems to be needlessly pissing on other people's hobbies, both people who collect vinyl and bands who want a physical copy of their album for posterity.
What a lot of people seem to be missing is that there is already a market for producing vinyl. So much so that new cutting shops and pressing plants are coming online. If these people can skip most of the expensive steps of getting a stamper cut, that will make it easier and cheaper for bands to produce vinyl, and as someone who's paid to have one of their albums pressed, that would be a welcome change.
No, most of them are cut digitally these days.
To increase the amount of playing time, you can vary the width of the grooves depending on the volume and frequency content (louder and more bassy parts need wider grooves), kind of like RLE coding in a way. To do this while cutting the master, you need to know what's going to happen in the next rotation of the disk.
This means you need two signals going into the cutting amplifier, one with the future signal, and one with the signal you're actually cutting to disk. Originally this was achieved using a modified tape deck with an extra playback head stuck way outside of the normal tape path. From the late 70s onwards, they used digital delays. The live signal (off tape, or a WAV file these days) is fed in as the 'future' signal, and the recorded signal is digitally delayed by 1.8 seconds or whatever it was.
There are a few places that still have the modified tape decks for real purists who want a 100% analogue signal chain, or at a pinch you can disable the variable pitch cutting, and have all the grooves exactly the same width as was done in the 50s and earlier, but you only get about 15 minutes per side.