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The effects of musical genre upon ease/degree of compression, [split from “What music genres do you listen to?”, thread 96042]
IgorC
post Jul 17 2012, 05:06
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QUOTE (db1989 @ Jul 16 2012, 18:37) *
Is that suggesting that developers should make accommodations (of what nature?) for particular genres, rather than remaining objective and fair by sticking with universal principles of psychoacoustics? If so, I'm not sure how to feel about that!

Any audio codec has a "difficult" and "easy" genres to compress. The information about average collection (roughly speaking) helps to determine how much encoder can increase or decrease bitrate on some particular genres and still would hit desired bitrate on big variety of genres.

This post has been edited by IgorC: Jul 17 2012, 05:12
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pawelq
post Jul 17 2012, 16:09
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QUOTE (IgorC @ Jul 17 2012, 00:06) *
Any audio codec has a "difficult" and "easy" genres to compress.



You are oversimplifying. "Classical music" is often considered a single genre*, yet the acoustic structure and consequently the ease/difficulty of compression vary enormously. For example, a harpsichord piece will be typically hard to compress due to very fast attacks and wide frequency range. A mellow and quiet full-orchestra piece, will be much easier. Respective examples from my collection (all FLAC, same quality) are up to 983 kbps for a two-harpsichord piece by Bach vs. 523 kbps for a slow movement of Beethoven's symphony or 418 kbps for a slow movement of Mozart's piano concerto

*which is misleading in the first place, as you can probably find much more musical and/or textural variety within output of a single classical composer, or sometimes within one piece, let alone the "classical" genre spanning ~500 years of history of music, than in entire "genres" of popular music.


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greynol
post Jul 19 2012, 05:00
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There is no need for ABX here unless you wish to demonstrate that the original and the distorted versions of harpsichord giving rise to different bitrates using the same configured quality setting sound different.

I believe there is some merit to the notion that different genres require different bitrates (lossy or lossless) on average and that for classical music, harpsichord is a well known exception.

Whether someone may be able to make good use of genres in order to make better/more efficient coding decisions is interesting but isn't something I've put much thought into personally. My initial response is that won't matter much, but I've been accused of being a pessimist on more than one occasion. wink.gif

This post has been edited by greynol: Jul 19 2012, 05:10


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pawelq
post Jul 20 2012, 04:51
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QUOTE (greynol @ Jul 19 2012, 00:00) *
There is no need for ABX here unless you wish to demonstrate that the original and the distorted versions of harpsichord giving rise to different bitrates using the same configured quality setting sound different.
I only wanted to show that they enode to different bitrates at the same q. I even don't know how ABX could be used meaningfully in the context of that test. Ideally, I would prefer to show that the encoded version are degraded by lossy compression to the same degree, but I can't see how to do it even if I used very aggresive compression that would produce audible degradation - because the originals were different,.


QUOTE (greynol @ Jul 19 2012, 00:00) *
I believe there is some merit to the notion that different genres require different bitrates (lossy or lossless) on average and that for classical music, harpsichord is a well known exception.
I started doing some tests and looks like you and IgorC are much more right than I originally thought, at least for lossless. At first glance it looks like you might be not so much right about lossy, but I am going to do some more tests and I'll definitely come back to the thread with results. By the way, is there a way to quickly export/copy specific information about all files in a foobar2000 playlist? I would like to export name Tab code Tab bitrate Tab ReplayGain.


QUOTE (greynol @ Jul 19 2012, 00:00) *
Whether someone may be able to make good use of genres in order to make better/more efficient coding decisions
Again, I don't understand how using genre information in addition to (or instead of?) actual audio content could improve coding efficiency.

QUOTE (Porcus @ Jul 19 2012, 07:31) *
While it looks strange at first glance, I don't think the claim describes any unwanted behaviour for lossy codecs -- indeed, I think the fallacy of the argument is that a lossy was used to compare.


Consider the following procedure:
(1) This is pretty much like noise.
(2) Psychoacoustic model says this is not very useful to the listener.
(3) We need to discard 80 percent of the signal anyway, so we discard this noise-alike thing.

Reasonable? Certainly. I recently learned that certain codecs (AAC and MPC) even use it actively: rather than discarding it, which would be at the risk of tilting the tonal balance, they substitute noise with noise-alike signals which are easily compressable. Perceptual noise substitution, it is called.

So what would be the effect of adding noise to harpsichord if the above procedure works well?
Without noise, this is a complex signal. A VBR encoder will increase bitrate.
With noise, this is a noisy signal. If there are overtones up there, they will be buried in noise, hence become useless, hence can be discarded. VBR encoder doesn't anymore see the need for high bitrate.
That would be my explanation as well. By the way, the discussion that prompted me to do those tests was about lossy coding. The other person maintained that metal is more difficult to lossy-compress than classical because of being less harmonic, more noisy, more distorted, and more "mistuned". And he said that he could "metalicize" the harpsichord sample and make it even harder to compress. I showed that adding noise or distortion etc actually makes it easier to compress (when mesaured with bitrate at the same q setting). I think that in the case of lossy compression it is more about transients and much less about noise/distortion/inharmonicity.


QUOTE (IgorC @ Jul 19 2012, 11:41) *
At this point it's clear that we've talked about different things

I cannot exclude this possibility. So, again, what exactly the rationale of your genre poll in the context of improving audio encoders? And, by the way, does the item named "Classic" in your poll refer to so called "Classical music", i.e., to a certain tradition of Western educated music composed during last few centuries? Or to something else?


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dhromed
post Jul 20 2012, 09:44
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QUOTE (pawelq @ Jul 20 2012, 05:51) *
And he said that he could "metalicize" the harpsichord sample and make it even harder to compress. I showed that adding noise or distortion etc actually makes it easier to compress (when mesaured with bitrate at the same q setting).


Have you tried the same harpsichord treatment on FLAC? With lossless compression, adding noise and distortion should increase file size compared to the untreated compressed version.

My point is that "easy to compress" with lossy compression shouldn't just mean a bitrate reduction. I could zero all the samples. Or I could delete the file. Now that's compression! Of course there's zero quality left at all— but the compression was really easy!

In other words, with lossy encoding, something should only be called "easy to compress" if you can reduce the bitrate without introducing audible distortion. If you've manually added noise and distortion to the harpsichord, clearly that is not the case. You've only made it easier to compress by making the lossy-encoder's work easier, thus supporting your friend's point that metal is hard to compress (regardless of whether this is correct, mind you. Experimental results can support a false conclusion).

I hate to raise a comparison to GIF and Jpeg, but in the case I think it's merited: Photoshop's Save For Web has an option to add special noise to an image that makes it easier for it to be compressed as GIF. It often reduces quality but can also significantly reduce file size. Similarly, you can add a tiny bit of blur to an image destined for jpeg, and thus reduce filesize.

It's a form of tenderizing the meat, so to speak, before it's fed into the compression algorithm.

This post has been edited by dhromed: Jul 20 2012, 09:45
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