Audio Compression Primer

Hack Jandy writes "For those of you with a little extra time this afternoon, check out Sudhian's primer to all things concerning audio compression. The article details everything from DRM to CRC matrixes (with a healthy dosage of Ogg)."

Comments

128K should be enough for everyone

[killmister]

I know that even large radio stations use 128Kbit sampling frequency. I have heard musicians saying they cannot distinguish the difference between the audio sound played by CD and MP3 with 128Kbit encoding. I have switched from 128K to VBR 320K but just because "that is a good style".

Re:128K should be enough for everyone

[statusbar]

FM and AM radio transmissions have worse quality than 128 kbit mp3 anyways.

Just recently I finally heard the difference between a 128 kbit mp3 and the uncompressed version in a blind test. It required good speakers and amplifier. Some instruments in certain frequency bands were definitely quieter and some instruments had their stereo imaging slightly wrong. Some transaural 3-d effects were diminished. It surprised me to hear the difference because I know that my ears have been damaged by playing in loud bands.

--jeff++

Re:Is FLAC worth it?

[stratjakt]

Most of us aren't exactly audiophiles.

I'll go stereo to mono and reencode at 22khz for my tv captures. It sounds the same to me.

As for mp3s, etc, the only time I ever listen to it in the car, and there's so much ambient noise, it's not worth bothering. Hell, 128k joint stereo sounds like the CD to me, I don't know any better.

I don't listen to much music anymore. All the bullshit and RIAA and this is legal and blah blah blah, it's all killed music as an artform for me. I used to play guitar in bands, and love playing music. It's just dead to me now. White noise.

Re:Is FLAC worth it?

[itp]

I keep my entire CD collection on disk as FLAC, and then transcode to the lossy format(s) most useful to me at the time (currently Vorbis to play in my Rio Karma). If I ever need a new format I can go back to the FLAC and reencode without transcoding from another lossy format.

Re:Is FLAC worth it?

[Dogtanian]

Hell, 128k joint stereo sounds like the CD to me, I don't know any better.

Really seems to depend on the codec; I can get 128kbps MP3s with notlame that sound really good through moderately decent headphones, but I download other people's 128kbps MP3s and you can hear the artifacts clearly.

Have they been re-encoded once or more (losing quality), re-encoded from a slower bitrate, or was the encoder that did it just severely crap? Who knows.

I notice that 192kbps MP3s seem to be more common now than they were during my first wave of filesharing, I mean legally downloading...

BTW, the music business has been amoral and full of bullshit since.... well, the 1950s at least. The mafia had their fingers in a *lot* of pies at that time.

Re:Is FLAC worth it?

[pavon]

I was going to do this and then I realized that FLAC only cuts the file size in half, and like you said, disk is cheap. So I just ripped them to WAV, which can read by every encoder ever created on any platform, unlike flac which requires me to install extra software, and possibly go through a seperate step depending on if the encoder for the format of the week supports FLAC.

Re:I still hear MDCT distortions

[radish]

Not wanting to get some award for pedantry, but all music recording is "lossy". If you listen to a CD, you're not hearing the exact same sound you'd here in the studio, those cymbals sound diffrent due to sampling, quantization etc. So when it comes to "lossy compression" causing "artifacts" - it's only creating different artifiacts, there already were some.

Of course this doesn't go against what you're saying at all, other than calling FLAC "perfect" is wrong. It might be the same as the CD, but that has it's own problems.

Re:Is FLAC worth it?

[pla]

I keep my entire CD collection on disk as FLAC, and then transcode to the lossy format

Same here... I began a search last year for a Vorbis CD player, and found that they simply do not exist (I've heard rumors of a few available only in random SouthEast Asian countries, but that doesn't really do me a whole lot of good).

So rather than either transcode my OGGs to MP3s, or rip my CD collection again (for the third time... Boy did I every choose poorly to pick VQF the first time) to MP3 to keep alongside my OGGs (wasting twice as much room), I decided to just go for lossless.

Now, I can reencode to MP3 for portable devices. I can reencode to Vorbis for putting on a DVD to take to work or a friend's house (or anywhere I can use a PC to listen to it). I could encode to AAC to listen on an iPod, if I had one. And in an absolute worst-case scenario, I can create a bitwise-exact duplicate of my original CD if, for example, the dog eats it.

Disk space has grown cheap enough that, when I stopped to think about it, it looked like a no-brainer. It takes literally weeks to rip a largish collection of audio CDs. A 200GB HDD costs under $100. So, I ripped one last time to lossless, and will never need to touch those CDs again.

FLAC is often worth it.

[Venner]

I personally think 256kbps or even 192kbps is good. But it depends on your output (speakers, headphones) and more importantly your ears. Some people don't mind 92kbps while others won't settle for anything less than vinyl (usually people with $30k+ wrapped up in their setups...)

I have a decent mid-range receiver & set of speakers*. I had a friend of mine administer a blind listening test on me. I could pick out the FLAC encode vs. the Ogg "higher quality" (I think it was -q7 or -q8) encode about 75% of the time.

Most of the time I am content with a good Ogg encode (I mean, hell, I'd never have heard the difference if the samples weren't played back to back!) I generally only use FLAC for a) my favorite albums and b) classical music. Size wouldn't be an issue... but for the fact that I keep an oft-updated mirror of the data on a second computer. As drive space is become rather inexpensive, I forsee a time when lossless will be the way to go, except for portables.

*Ascend Acoustics CBM-300 stereo pair, HSU sub, and a HK AVR-325 receiver.

Re:FLAC is often worth it.

[Venner]

>>Just curious, what ogg encoder/decoder software were you using? Was it recent?

Oggenc, using libogg 1.0 I believe. Played back with winamp 5, whatever they use as their decoder. We also tried converting the Ogg back to a PCM wave file and burning the new and old wav to CD, to see if that made a difference.*

I'm not sure if there is a limitation on FLAC that makes it unable to carry more information than OGG, but remember that the real limitation would then be the CDs, which are mastered at 16bit/44.1kHz. I picked up several DVD-A disks on clearance and have been wanting to try them out. If nothing else, they should have a much better dynamic range than CD (and potentially SACD.) I just need a DVD-A player***.

The point is, DVD-A will have a ton more data to encode than what we currently have with CD - if anyone ever bypasses the much-harder-to-break-than-DVD-video encoding scheme.

*To be played back on a SACD* player, rather than a potentially noisy sound card jack.

**on loan from said friend.

***Regular DVD players play back a DD/DTS track, rather than the higher-quality DVD-A track. Even that much sounds nice.

Good background, but heavily biased

[bigberk]

(As an Engineer who has thoroughly studied ADC/DAC) I would say that the article presents a very good background on the issues of sampling and reconstruction of audio.

However, the rest of the article is approached from the heavily biased opinion point of an "audiophile", which the majority of the population is not. These audio experts have fantastic equipment and a keen sense of hearing, allowing them to distinguish between the subtle difference between high fidelity recording and playback. Such people like software like foobar2000 and care a lot about dynamic range, and for the most part think that lossy encoding is a shame. This is a bit about being picky, and a bit about showing off, but either way it's a minority viewpoint.

But such people are by far the minority of the public. Most of us don't get caught up in the subtle details of audio recording and playback, partially because we don't care, and partially because we don't have the fine equipment (electronics and human ear) to notice such things. So the article for instance completely dismisses lossy encoding, even though this is by far the most exciting frontier of modern audio compression. You can get 64 kbps (ogg vorbis) or 32 kbps (aac) streams that sound amazing to most people, as good as FM radio.

As an Engineer that is what I find exciting, because we can transport "essentially the same" amount of media in far, far less bandwidth than it required a decade ago. And the efficiency is improving all the time, ditto for video.

Re:AAC

[Skuto]

AAC is *much LESS* expensive than MP3. Just compare the licensing costs from Vialicensing (AAC) vs Thomson (MP3).

The parent is plain wrong. ("Don't believe all you read on the internet, kids")