His Productions wrote:
Where can I find the bits per sample for an MP3 in AA cs6?
Er, you don't...
And this is for two reasons; firstly, MP3 is a compressed medium and uses variable sample depths as part of the masking mechanism. Bits considered to be inaudible are encoded at much reduced depth - it's called a 'coding gain' and how the compression is achieved. The lower the rate, the more compression there is and the worse it sounds. So there is no 'bit depth' as such, although notionally, it's supposedly 16 for the non-compressed sections I believe.
Secondly, when you open an MP3 in Audition, it's decoded to the software's native format - wav. And that would be at whatever you've set it to open MP3 files at; notionally 16 bit int (as above), but I believe that Audition will decode them quite happily as 32-bit Floating Point as well.
This isn't the same as the sample rate - that's got everything to do with either improving or wrecking the sound by limiting the speed at which slices of sound are cut up by the encoder to be worked on, and then spat out the other end. And, all of this is a simplified explanation of what happens in an MP3; the actual detail is pretty complex.
So, there really is no way to click or right click on a file a know what kbps the file was compressed to?
While I'm able to listen to a file and "know" whether the quality is reasonable for my work, my clients are not. For transfer via FTP, our clients convert their .wav files to 44100hz, 128kbps minimum MP3's.
I need to be able to make sure that they've batched it down to 128 Kbps ... If proofing that is AA isn't possible , do you have any suggestions?
Well, as Steve points out, your solution has to come before you open the file in Audition since, once Audition has opened it, it's no long MP3--it's uncompressed .wav.
However, if you don't mind a bit of math (and if Macs give you the same info as my PC) you can work it out.
When looking at files on my PC, if I hover over an MP3, it tells me the file size and the duration. The file I just experimented on said it was 4.65MB and 5:04.
Since (in this case at least) there are 8 bits to a byte, multiply the 4.65 by 8 then divide by 304 (the number of seconds in 5:04). The result isn't exactly 128kbps (that 4.65 is obviously rounded off) but it's close enough to 128,000 for me to be pretty sure it's at 128 kbps.
Long winded I know...but maybe you could knock up a spread sheet showing the number of bits to expect at 128kbps for every 10 seconds duration (or whatever) and, as long as you files size is bigger than that, you've hit your minimum.
I did the sum and came up with 113kbps! Yes it's sort-of possible to work out what the compression ratio is, but what's the point? Right-clicking on an MP3 and going to the advanced properties will tell you all that anyway, as it's in the header information. It has to be there, otherwise the decoder wouldn't have the faintest idea what to do with it.
What it doesn't tell you though is anything about the quality of the file, because it doesn't indicate what it was encoded from. A good original coded at 128k can easily sound better than one coded at 320k from a crap source. The compression ratio per se means nothing at all, except to indicate the best it could possibly be. Certainly doesn't tell you the worst, because it would come out at the same answer from an 8-bit original as it would from a 16 or 32-bit one - for 128k, that's about 938k per minute of stereo audio - it's compressed at around 11:1 (depending slightly on the complexity of the audio) of the 16-bit file. Or 22:1 of the 32-bit one. See the problem?
To put it starkly - a 320kbps MP3 file made from an 8-bit original will almost certainly sound rather worse than the same material, only 16 or 32-bit, encoded as a 128kbps MP3. Aside from any other considerations, the noise floor will be lower in the 128k one!
Also, I suspect that the OP actually means kbps, which is seconds, not samples...
Well, live and learn! I'm not sure I'll use that feature much but it's good to know it's there.
At least it confirms what my rough mental math told me. It would have been embarrassing if it'd turn out NOT to be 128bps CBR!.