WAV - the differences

[Kamakura]

I was trying to save an audio file as a .wav but it's not quite that simple.
Audition offers these varieties of wav:

A/mu-Law Wave
ACM Waveform
DVI/IMA ADPCM
Microsoft ADPCM
Windows PCM

I assume they are different codecs. but what are the differences, and is there a standard?

[deshead]

PCM is the standard. That's your basic 16 bits per sample, uncompressed audio file, exactly what you'd burn to CD. PCM WAV files are universally supported.

The others are, as you assumed, codecs. They all perform some kind of compression on the audio to reduce the file size. (ADPCM being the simplest: it uses 4 bits per sample instead of 16 ... So it sounds like crap.) The codecs aren't universal, though. That is, the WAV file will only be playable on a system that supports the codec.

Here're some more details if you want:
http://support.microsoft.com/kb/q89879/
http://www.nch.com.au/acm/
http://www.unrelatedinventions.com/Audi ... ..wav..htm


But in short: use the Windows PCM setting, and ignore the others.

[boltoph]

PCM is the standard. That's your basic 16 bits per sample, uncompressed audio file, exactly what you'd burn to CD. PCM WAV files are universally supported.

The others are, as you assumed, codecs.

How about AIF? is it the same as AIFF? And then there's SD2 and QT formats? I'm confused. I'll give 'r a "broadcast WAV", damnit.

[HeuristicsInc]

AIF == AIFF. Back in the old days of dos you were allowed 8+3 in filenames, that is, 8 characters in the name and 3 characters in the extension. e.g. BILL_MUS.AIF. It was pretty annoying.
QT is QuickTime, a Mac developed thing, I believe but there is QuickTime for Windows too. I wouldn't bother with it. SD2 no idea.
-bill

[fluffy]

(ADPCM being the simplest: it uses 4 bits per sample instead of 16 ... So it sounds like crap.)

A 320kbps mp3 stores each sample using only 4 bits on average, but yet it doesn't sound like crap.

ADPCM basically stores each sample as a difference between the sample and what that sample would be predicted to be based on the previous samples. It's actually quite good in most circumstances, and near-lossless (but not actually lossless) as long as the waveform doesn't deviate too widely from the prediction model.

WAV is just a different name for RIFF, which is a sibling to AIFF (both coming from IFF). They are all essentially the same - a generic container which stores multiple chunks of data. They can store images and video and metadata and all that other fun junk too. WAVs can even store mp3 data if you want (the original Fraunhofer CODEC actually put the mp3 stream into a WAV container instead of an MPEG one).

The thing about file names is that they're there for the user's benefit, not for the computer's benefit. There's no structural difference between an mpg, mp2, or mp3 file, or between m2a or, m2v, or between m4v, m4a, m4p, aac, mov, qt, etc., they're just there to tell the user what kind of file it is or which application to use to open it by default (which just happens to usually be taken care of by the file browser these days).

As far as the difference between mu-law (often written u-law as a mu symbol looks like a u) and linear PCM, u-law is stored in a format which gives more precision to low signal levels, which often gives it better quality (very similar to how monitor response is non-linear). It was used a lot back when most sound hardware was only 8-bit and so it was important to make the most of the precision. In practice, 16-bit linear is about as good as it's going to get, at least for final mastering.

In general, 16-bit linear PCM WAV is the most compatible with other tools.

[Kamakura]

Thanks a lot!

[stueym]

I love how there is this aquifer of knowledge among the community that is suddenly tapped and produces these wonderful educational moments.

Thanks gentlemen!