Why is MPC perceived to be the best?, (an off-topic audio encoding discussion) Options

[ScorLibran]

This is a question that has floated through my mind for most of a year, but only yesterday became more clear to me.

Actually, it's a two-part question...

... 1. Is MPC commonly accepted among the HA community as the best psychoacoustic encoding format? (i.e., the most efficient at achieving perceptual transparency.)

... 2. If so, why?

The first item I've heard stated quite frequently, but have never seen any results of "transparency threshold tests" that would reveal the superior efficiency of MPC. I've heard that MPC uses superior encoding technology, but I'm referring more to the end result of such development efforts...the perceived sound quality, as measured against other codecs at the point of perceptual transparency for a significant number of people.

These concerns on my part were born from a post I made here, where the points of MPC statistically tying other formats at 128kbps, but no other known test results existing, were brought up. The thread portion ended up in the recycle bin, but I'm taking the chance that my concerns about calling MPC "the best" weren't the reason it was put there.

Hence, I want to bring up this idea in a different context in the off-topic forum (in the hope that this will be the correct area for it).

What I'd like to see, for instance, for the education of myself and others, would be a results summary like the following (though this is a very simplistic example)...

Format............Perceptual Transparency Threshold (nominal bitrate across samples tested)
MPC.................nnn kbps
AAC.................nnn kbps
Vorbis..............nnn kbps

...and so forth

Granted, VBR is more efficient at mid-bitrates and up, and quality-based VBR modes aren't bitrate centric, but we need some means of measurement and comparison between codecs in this context, so if not calling it "nominal bitrate", then perhaps "average filesize per minute of audio across all samples"

Perceptual Transparency Threshold could have a fixed target, like >90% samples with 5.0 subjective ratings, and non-differentiable from reference with ABX testing.

This kind of test has been discussed before, and has been mostly viewed as having little "real-world value". And I agree. Roberto's tests are much more relevant for most music listeners, and for determining the best formats for useful purposes like streaming audio, portable players, etc.

Many of us (including me) have trouble testing even these bitrate ranges, so higher ones would be even more tedious, and would answer not as many pressing questions.

My point, though, is how can MPC be called "the best for achieving transparency" without a test such as this? (Because so far it's been shown to be only "among the best" at lower rates.)

[music_man_mpc]

For narrowing down quality settings use binary search, e.g.:

q5 pass
q4 fail
q4.5 fail
q4.75 pass
q4.625 pass

ad nauseam. At some point it will be narrow enough to warrant a stop.

To trim down the total number of tests, shrink your goal. If you seek to verify that MPC is superior to all codecs, don't try to calculate the "transparency threshold" for each codec, just locate a bitrate that is transparent under MPC and not under the codec in question.

Finally, if you do separate tests by codec, you will open yourself up to placebo. If people strongly believe that a particular setup is transparent, they may relax and not look hard for differences. The solution to this is to provide, each time, a set of flacs without identifying what the codecs are, and reveal that only after the test.

For example, here's a plan:

Round 1:

MPC -q5 and Vorbis, LAME, WMA, AAC, whatever, bitrate-matched to MPC

Suppose ABX reveals that MPC, Vorbis and AAC pass, LAME and WMA fail => these two are dropped from future tests.

Round 2: MPC -q4 and -q4.5; two each of Vorbis and AAC bitrate-matched to the two MPC's

Suppose everything at MPC -q4 bitrate fails, Vorbis fails, MPC -q4.5 and AAC counterpart pass => drop Vorbis.

Round 3: MPC -q4.125, -q4.25, -q4.325 with AAC counterparts.

=> should settle it.

Excellent system Doctor. I bet this would be a much simpler and more efficient method than my brute force technique. However we need to guess at what --quality values are going to be used ahead of time so we can find out the corresponding command lines for the other codecs. Once we have some idea what --quality values will *probably* be tested, we should try to find their nominal bitrates. To do this I propose that several of us encode a whole bunch of random tracks at a specific --quality value and then post the average bitrate we got (you can calculate with this) along with the number of tracks encoded (try not to include tracks of silence or tracks with long periods of silence). Then we can get the mean by multiplying those two numbers together and adding all the products, as well as all the track numbers together, then dividing total products by total tracks.

Example:

Person 1: A = [Number of tracks]; B = [Average bitrate]
Person 2: C = [Number of tracks]; D = [Average bitrate]
Person 3: E = [Number of tracks]; F = [Average bitrate]

Total Average = (A×B+C×D+E×F)/(A+C+E)

I already tested 394 tracks at --quality 4.1 and got an average bitrate of 128kb/s (oddly enough). Don't follow my lead, please as I'm not sure if we will be using --quality 4.1 yet. I did this before Doctor's post.