[FFmpeg-user] Compare quality of 2 audio files

[Rodolfo Medina]

Rodolfo Medina <rodolfo.medina at gmail.com> writes:

> Harold Tessmann <htessmann at control-tec.com> writes:
>
>> On Thu, Jun 29, 2017 at 12:37 PM, Moritz Barsnick <barsnick at gmx.net> wrote:
>>
>>> And unlike video, it seems there are few, if any, methods to measure
>>> the *perceived* quality of audio. Check here for some ramblings:
>>> https://stackoverflow.com/questions/2945531/determining-
>>> the-best-audio-quality
>>>
>>> But I challange you to find an algorithm which can compare two audio
>>> tracks. (And you need someone with a good ear to confirm its findings.
>>> Or reference material and encodings such as SQAM.) But if you do find
>>> it, and it's "free" to use, please implement an ffmpeg filter with it.
>>> :-)
>>>
>>
>> To continue along those lines, I don’t think this is even a problem that
>> one can precisely define. I will start by acknowledging that there exists a
>> boundary where you can define audio quality objectively. Clipping, for
>> instance, destroys sound data, and is objectively bad <
>> https://en.wikipedia.org/wiki/Loudness_war> (but even then, some musicians
>> or sound designers may want that, for industrial or other effects). But
>> there is a difference between objective quality and what people want.
>> Consider the ability of a display to reproduce an image accurately. You can
>> make an objective comparison, but if you go by the display section of an
>> electronics store, you’d find out that people tend to like oversaturated,
>> objectively worse, color <
>> http://www.flatpanelshd.com/focus.php?subaction=showfull&id=1328263571>.
>>
>> And then you have to consider the environment of your audience, which you
>> can’t necessarily control. Audio played in a car has to contend with road
>> noise, while pictures on a TV will look significantly different in a bright
>> store vs. a customer’s home <
>> https://www.cnet.com/news/why-do-plasma-tvs-look-washed-out-in-the-store/>.
>>
>> And then there’s the question of how much quality your audience can detect.
>> The MythBusters did a test with different grades of vodka and determined
>> that yes, an expert can taste the difference between high end and cheap
>> liquor, but your average person doesn’t have so discriminating a palate <
>> http://kwc.org/mythbusters/2006/04/episode_50_bullets_fired_up_vo.html>. So
>> even if you did come up with a good metric, perhaps you don’t _want_ to
>> check it against an audiophile, or a recording engineer, or somebody who
>> has particularly good hearing.
>
>
> But suppose you have a song, or any piece of music...  a certain particular
> precise recording, just that one...  and that you find in internet two mp3
> different files of that song, from two different web sites, both same size in
> megabytes.  Suppose that the test with Audacity, which we have earlier much
> spoken of, reveals a difference between them: this means that a portion of
> the original WAV file during the MP3 conversion has been discarded in more
> quantity in, say, file1.mp3 than in file2.mp3 (in fact it can be heared).  Or
> also suppose that both files are in wav format but still Audacity reveals a
> difference between them (because one of them could be - as far as we know -
> the result of a previous unknown conversion).  Then I expect if would be
> technically possible that we could give an algebraic plus or minus sign to
> that discarded portion and tell - objectively and not by a simple personal
> listening feeling - which of the two is the one that contains more
> information and which less - that's what I would reasonably expect.


It's as if in Algebra we can do |a - b| but don't know wether it's a < b or b <
a...

Rodolfo