Rodolfo Medina <[email protected]> writes: > Harold Tessmann <[email protected]> writes: > >> On Thu, Jun 29, 2017 at 12:37 PM, Moritz Barsnick <[email protected]> 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 _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
