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LAME's resampling leaves something to be desired
eamon123
post Oct 15 2012, 20:16
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http://shibatch.sourceforge.net/ is a good resampler. It beats lame in quality every time. Here is an example:

Yes I retested Baba O'Reilly and it sounded noticibly better with ssrc.

I did

FLAC 88.2 > lame.exe -S --noreplaygain -b 32 --lowpass 10 --resample 24 - %d
VS
FLAC 88.2 > WAV > ssrc.exe --rate 24000 --bits 16 > lame.exe -S --noreplaygain -b 32 --lowpass 10 - %d

in ABX and got 14/16 (0.2% prob of guessing). I was hearing a whole different type of artifact that I have either never heard before or just never listened for before. I was 5/2 up when I started listening to the bass drum and it just sounded fuller, warmer and louder in ssrc. It was then that I noticed that there was a shrill artifact at about 9 kHz at the same time as the drum beat in question. It was obvious in both files, but louder in the LAME version. Up until now the bass drum "masked" it, "masking" is seriously like an aural illusion, that bass drum sounded fine before I heard the shrill in one and then I heard it in the other, I was dumbfounded! After that I just listened for that beep and the louder one was LAME. LAME should really look into their resampler, a lot of people are downsamping high res FLACs these days!

I feel like I did the first time I discovered that I had a blind spot on my retina that I could "discover" at will with carefully engineered designs and some ordinated displacement of said designs. Discovering the nature of my aural blind spots first hand I can only describe myself as feeling enlightened!

Maybe that shrill noise is due to a crappy lpf in LAME?

https://rapidshare.com/files/1612342437/ssrc.vs.lame.zip





ssrc is foss, maybe the LAME devs would like to copy some of it's code?
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eamon123
post Oct 17 2012, 02:39
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I'm using that as a particularly glaring example that I can show on the screen. If you listen to the two files, you can find extra artifacts in the LAME resampled file throughout. Do your own tests even. To quote someone else on the reason as to why this is the case:

QUOTE
What makes this probably worse than usual is that the kind of noise artefacts produced by bad digital filters can easily mislead lossy psycho-acoustically modelled encoders to allocate spectral buckets to these artefacts rather than "real" content.


QUOTE
something innocuous like the steepness of the cutoff

The only difference is the resampling algorithm so it must be something about the resampling process that is sub-standard.

QUOTE
Not all low pass filters are created equally, especially when the order of a "perfect" filter exceeds a few thousand, as few resamplers will bother with that.

To be sure you're not suffering from resampler implementation bias, you should do manual resampling with SSRC in "high quality" mode using the standalone tool written by SHIBATA Naoki.

Outside of proprietary closed-source resamplers, I'd assume anything less than Shibata's is broken. 44.1->48/32/24 resampling requires a relatively complex filter to do it "perfectly". (One of the reasons why 44.1KHz was chosen even though more "harmonic" values were known or even proposed at the time was precisely to make this kind of resampling "hard" for consumers.) The resampling ratio is a beast, in any event: 160:147 (for 44.1->48). EEs/DSP jocks will immediately understand the high order filter needed to do this job perfectly.


They both have the same cutoff, I specified --lowpass 10 which has a default range of 15%. The input wav from ssrc was cut off well above 11.5 kHz so after the lpf the cutoff in both is exactly the same.

This post has been edited by eamon123: Oct 17 2012, 02:53
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