[polshaw]

My somewhat educated take on that is that 'perceptually lossless' refers to quality at which the source cannot be reliably picked from the source/encode in any sort of test that would pass as scientific, possibly outside of a few very rare edge cases (sound samples, not people). This happens at lower bitrates than many people might imagine, IIRC v2 lame (~192kbps) has not been reliably identified, nor vorbis v6 (~160kbps). So their claim of 'perceptually lossless' at 256kbps is neither surprising or impressive. (it may be competitive/better at those high bitrates and they are just being conservative with the claims).

[Cyranix]

Not a scientific test by any means, but for a quick and dirty take on the matter, here's the Great MP3 Bitrate Experiment courtesy of Coding Horror: http://www.codinghorror.com/blog/2012/06/concluding-the-grea...

[makmanalp]

So if I'm getting this correctly, a computer test (not a person) has to look at two clips of audio and tell which is the source and which is encoded?

I'm surprised that 192k is actually indistinguishable. I thought some humans could tell the difference there.

[pgeorgi]

Usually it's double blinded ABX testing: A computer program gives you: Encoding A, encoding B, unknown encoding A or B. You have to choose if X is A, or X is B.

One of the encodings will be "uncompressed" when testing if the format in question is perceptually lossless.

Repeat that a couple hundred times with many different listeners using standardized samples and programs (doom9, an audiophile forum, does such runs every now and then), and you get a rather good idea on what's going on.

As for the 192kbps: It also depends on the algorithms used. bladeenc or 8Hz-mp3 back then created 320kbps files where you can easily hear the difference. Current lame builds at 192kbps? not so much.

[cageface]

No a computer can trivially tell the difference.

But most people can't distinguish a properly encoded mp3 from the original at 192kbits and often much lower than that.

[polshaw]

Worth noting it is 'v2', which is a specific setting with a specific encoder (lame) that creates a variable bitrate file which averages around 192kbps.

That is very different to just setting itunes to 192 and expecting 'perceptually lossless'.