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Comment by nitrogen | Hacker News Reader

I found the ringing in the new 16kHz sample to be a bit bothersome. It sounds like theres a tonal peak in the frequency response near the upper end of the frequency range. The peak would be less bothersome if it were spread out more.

Edit: is the new resampling done by something like Shibatch SSRC or libsamplerate's SRC?

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It sounds a bit better outside of Flash, actually. Flash prefers 22050 or 44100 audio and doesn't do a great job of resampling others up to 44100 (which I think is what happens behind the scenes). Give it a listen in Chrome or some such and see what you think.

We aren't using those libraries right now, but we'll check them out. How do they compare to something like SoX?

I haven't used SoX extensively since Mandriva was called Mandrake. It looks like the newest version of SoX has a very good converter. The comparison graphs I just found and linked below show that the different converters seem to optimize for different parameters; Shibatch SSRC appears to focus on passband width, while libsamplerate's Secret Rabit Code has better time domain response. If you're using SoX VHQ, you probably can't do much better, unless you find that its time domain response causes undesirable artifacts.

As for the 16kHz sample, listening to the .m4a files directly did give much better results than playing them through Flash.

Anyway, good luck with ZenCoder.

http://sox.sourceforge.net/SoX/Resampling

http://src.infinitewave.ca/

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