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potential mp3 difficulties, how important are these factors?
post Apr 8 2007, 22:49
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I've read a few contentions against lossy compression and another against many ABX test. I'm wondering if there is any established data to confirm or refute them, or if these factors have been taken into account in the development of LAME.

** The response of different speakers to the same power amplifier signals varies more or less everywhere across the frequency spectrum.
** The audio delivered to the ears from any given speaker system varies considerably from room to room due to room response and speaker-room interactions (not to mention the position of the listerner in the room).

Both of these are true and can be objectively measured. The contention is that psychoaccoustic models, where they are based on masking, are thus not completely valid except for the exact listening circumstance under which they were developed. This is because masking will differ somewhat under the different listening conditions, making transparency difficult or impossible to achieve in everyone's living room.

It seems well established that the listening room must be properly compensated to avoid adverse effects on what is heard. ‘Masking" of a type takes place at various frequency ranges in most "raw" rooms due to enhancements and cancellations from room reflections.

It is also well established that the majority of home music speakers, even rather expensive ones, are designed to deliver something other than exactly what is fed into them. This is why professional monitors exist.

The question is whether or not these factors are taken into account in encoding. If not, then the audiophile contention, that even the best mp3s are not transparent if the equipment is good enough, may have a basis in fact. Of course, in principal, ABX testing could be applied to investigating these claims. Have they? I suspect that most people who make such claims believe the differences are so apparent that further testing is irrelevant. It would probably take a skeptic -- with access to such equipment -- to make such tests.

The ABX testing "difficulty" contention is that the auditory system suffers from reduced discrimination ability after some time due to fatigue, and that this time can be as short as 20 minutes. A single ABX test probably most often takes less time, but more extensive tests probably run much longer. Is this a know factor? Is it considered relevant to encoder development?
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post Apr 9 2007, 02:35
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QUOTE (AndyH-ha @ Apr 8 2007, 23:49) *
The contention is that psychoaccoustic models, where they are based on masking, are thus not completely valid except for the exact listening circumstance under which they were developed.

AFAIK, psycho-acoustic models are not developed under any listening circumstances, but with scientific data about the inner workings of human hearing. They are based on what (most) humans can't hear, not on what some developer's speaker system and room conditions sound like.
Of course, some otherwise audible artifacts can be masked by cheap speakers, but if your hearing is not capable of recognizing a certain artifact (a lowpass, for example), even the world's best listening equipment won't do the trick. Cheap equipment only increases the masking threshold further. That audiophile blabber intends to justify expensive "high-end" record players and other stuff IMO.

Even the best MP3s are not transparent if the listener is good enough.

Nothing is impossible if you don't need to do it yourself.
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Posts in this topic
- AndyH-ha   potential mp3 difficulties   Apr 8 2007, 22:49
- - LANjackal   Pretty deep post there. I think the point of ABX t...   Apr 9 2007, 01:57
|- - Lyx   QUOTE (LANjackal @ Apr 9 2007, 02:57) Pre...   Apr 12 2007, 05:05
- - Light-Fire   QUOTE (AndyH-ha @ Apr 8 2007, 16:49)...   Apr 9 2007, 02:34
- - Silversight   QUOTE (AndyH-ha @ Apr 8 2007, 23:49)...   Apr 9 2007, 02:35
|- - kjoonlee   QUOTE (Silversight @ Apr 9 2007, 02:35) Q...   Apr 9 2007, 06:09
|- - pepoluan   QUOTE (kjoonlee @ Apr 9 2007, 12:09) I wa...   Apr 9 2007, 07:04
|- - Silversight   QUOTE (kjoonlee @ Apr 9 2007, 07:09) I wa...   Apr 9 2007, 23:40
- - AndyH-ha   Fatigue Fatigue and acclimation are common for ot...   Apr 9 2007, 06:04
|- - Light-Fire   QUOTE (AndyH-ha @ Apr 9 2007, 00:04)...   Apr 9 2007, 07:00
- - MichaelW   QUOTE (AndyH-ha @ Apr 8 2007, 15:49)...   Apr 9 2007, 06:25
- - AndyH-ha   Yes, if such fatigue is real, it may well effect a...   Apr 9 2007, 06:57
- - AndyH-ha   QUOTE You can quickly (seconds) switch between fil...   Apr 9 2007, 09:01
|- - Light-Fire   QUOTE (AndyH-ha @ Apr 9 2007, 03:01)...   Apr 10 2007, 01:42
- - Steve Grant   A very interesting subject. If you were to think ...   Apr 9 2007, 10:54
- - AndyH-ha   I did not challenge anything. I ask some questions...   Apr 10 2007, 04:44
- - Gabriel   All psychoacoustic-based lossy encoders are using ...   Apr 10 2007, 09:53
- - pdq   If your sound reproduction system deviates signifi...   Apr 10 2007, 13:59
- - Axon   Speakers regularly vary by 10-20db in their freque...   Apr 10 2007, 15:15
- - Axon   Bump. I'm not letting this one die. Is everybo...   Apr 11 2007, 16:38
- - AndyH-ha   QUOTE All psychoacoustic-based lossy encoders are ...   Apr 11 2007, 19:29
|- - Polouess   QUOTE (AndyH-ha @ Apr 11 2007, 20:29...   Apr 11 2007, 20:14
- - Axon   I guess the basic problem is that there's no c...   Apr 11 2007, 20:07
- - MichaelW   Has anyone done tests to see if two samples can be...   Apr 11 2007, 23:56
- - 2Bdecided   Last point first: Clearly a particular lossy encod...   Apr 15 2007, 04:49

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