Author Topic: MP3 or WAV different result?  (Read 4711 times)

Apfelmatsch

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MP3 or WAV different result?
« on: April 21, 2015, 21:50:40 »
Hello,

I'd like to know, if it will have an effect on the test results, if I use MP3s or WAV (i.e. AIFF = CD-audio).

I imagine, since MP3 is more compressed, the used codec might have e.g. compressed the loudness of the music, too.

I have to compare interpretations of a neo-romantic/modern symphony and while getting MP3s of all interpretations would be the easiest and cheapest way, I fear I will miss something of the original that got compressed out of a studio file, while I think the wav/Aiff/CD-Audio will have more of the orifinal studio/live-recording.
Also I guess, I should not mix MP3 and WAV interpretations, right?
Also, I guess, I should not use some MP3s from Spotify and compare to some MP3s converted from CD-audio with iTunes or mepgstreamclip or different MP3-portals/streaming-services, right?

Well, of course, I could just test it and make it part of the text I am working on.

Thank you.
« Last Edit: April 24, 2015, 13:57:33 by Apfelmatsch »

Apfelmatsch

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Re: MP3 or WAV different result?
« Reply #1 on: April 24, 2015, 14:02:56 »
Does no one have an answer or did I ask a stupid question?

cannam

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Re: MP3 or WAV different result?
« Reply #2 on: April 24, 2015, 14:17:54 »
Hi there -- please don't worry about asking stupid questions, this is a very reasonable one.

Generally speaking the compression used for mp3s does not make a difference to dynamics and the like -- it has nothing in common with the dynamic range compression typically used for e.g. radio broadcast. A good-quality mp3 should give you essentially the same results as the wav version for reasonably robust audio features, although you may get different results for very low-level features (such as those sensitive to inaudibly high frequencies appearing in the signal).

There have been various publications on this subject, for example here: http://www.terasoft.com.tw/conf/ismir2014/proceedings/T103_326_Paper.pdf

Do be alert, though, to the fact that there may be padding differences between different encodings or releases of the same piece (i.e. different amounts of silence at end or beginning).

Chris

Apfelmatsch

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Re: MP3 or WAV different result?
« Reply #3 on: April 29, 2015, 14:21:32 »
Thank you for answering!

OK, the pdf you linked does sugguest (as you somewhat gave a hint to) that a minimum of aprox. 160kbps is needed to not affect the research results.

I am still a bit insecure, though. There seems to be a special case: http://www.pleasurizemusic.com/en/why-do-data-compression-processes-mp3-example-strongly-affect-loud-masters-no-headroom What is described here, is that different from the loudness war phenomenon (which will not play a role here)? If the studio master has already been made very loud, it will get problematic after compression. So let's say from the tape, they made an audio CD setting the loudest point as high as possible or even upping the most silent points of the tape. I guess when the MP3 seller / the label then compressed that to mp3 you get a similar phenomenon like in loudness war (I guess that was what you were referencing to radio broadcast situations etc.).

Well, ok. I can never know, what the studio guy did to the tape. When the conductor conducted from pianossimo to fortissimo and the studio guy just equalized that, I can't do anything about it. I probably won't even know, if he did change the conductors intents.

Apart from that is the loudness war stuff been done to classical music, too? Maybe in a false attempt to make it more impressive to the listener?

Another thought: according to the pdf, in my tests, could I go so far and even compare 256kbps mp3s (as I guess that is the most likely to be found) or 320kbps mp3s with FLAC/ALAC and wav/aiff? Like conductor 1 as MP3 and conductor 2 as wav (which would be derived from FLAC) and compare them?

Maybe I should even compare mp3s of the same conductor and same recording against each other, maybe I find that different mp3 sellers used different quality compressors (given that all use 256mbps).

Since I have a Mac and Sonicvisualizer does only take wav I will also have to look out for something that can convert FLAC (PC) to wav and ALAC (Mac) to wav and maybe even aiff (Mac) to wav (PC).