I think it's nice because the difference is not masked by the rest of the sample (which are usually higher in volume).
Ok after some other discussion that prodded me into this I decided to give it a try again. That is, I calculated the pure loss with mp3 and mpc encoders in CoolEdit (Mix Paste, both channels inverted & Overlap) and listened the pure loss in each case with different quality settings....Could you tell me your points why this is not a good way of objectively evaluating how successful a lossy codec is?
Can't we conclude anything objectively or subjectively by observing the pure loss?
(...) I observed that with mp3 standard preset, I can still figure out the melody because I can still hear some instruments (probably because of low pass filter). With MPC I hear the swoosh sound intensifying in some parts of the sample(...) It sounds to me the discarded information is more tolerable a loss in q4 MPC than lame standard mp3 3.93.1.
Just a question : have you decoded your mp3 first with LAME, in order to remove the additional samples ? If not, your test is biased : Fhg decoding engine will maintain the 'gap'.
The stronger difference (= noise) isn't necessary the most ABXable file.
I think we may conclude if the volume [of the difference file] is low then lossy encoder does a better job (as is shown by increasing quality settings give rise to that effect). Also we can somehow conclude if the "loss" consists of random noise and the original signal is not noticeable, then lossy encoder is doing a better job, can't we?
Some one find the thread - I can't bare to type it all again, and I have to go and book a holiday!
@tigre:For point 1) we may assume the lossy encoder would not shift the phase of the original. And I don't think it does.
Here's another issue to chew on..Even allowing/assuming/accepting that the difference file doesn't tell you the quality, what do you think of using it as a crib in ABX'ing? That is, using thedifference file to identify artifacts which you go and try to find in an ABX betweenthe original and encoded files, knowing exactly where to look?Is it that all is fair as long as in the end you can identify the encoded file in a blind test, oris it cheating a valid model if you could never pick the encoded file without "looking underthe covers" at the diff file?
How could the sum of those frequencies be higher than the original, if none of the frequencies has its phase shifted? And exactly that happens during clippings.
You are very likely to imagine that you hear the diff signal within the coded signal, once you've learnt it. But if it's pure imagination, ABX will take care of that!
This is interesting... Diff1 = -Diff2 by your own definition, so the question comes down to if you can hear the difference between the original and an inverted waveform. My uneducated guess would be that you can't. Other opinions?