I've noticed soft but very distinct rippling sounds (perhaps artifcacts?) in some of my aps files. I've noticed them only on quiet and acoustic material, and generally when the coding is around 128kbps.

To narrow down the possible problems, I ripped a straight WAV file. Didn't notice any ripples.

I encoded a file at a cbr 320kbps with alt-preset and the ripples came back.

Does anyone know where this might be coming from?

Some songs where it is most noticeable:

Johnny Cash - Delia's Gone from "American Recordings" (a couple from 0:20-0:25)
John Lennon - Working Class Hero from "Plastic Ono Band"
The Shins - New Slang from "Oh, Inverted World"

Oh, and I used LAME 3.93.1 as well as 3.90.3. Same results with both.

Can you grab and post some specific samples along with a description of the rippling? Once other people can hear what you hear, we'll be able to find out what's causing it.

(If 320kbs is causing the same rippling, it might be a flaw in the mp3 codec itself.)

-Steve

(Edit: spellin')

Can you ABX the original with the encoded files ?

Edit : see FAQ, and rule 8 of the Terms of Service

What do you use for playback?
Have you tried foobar2000's diskwriter (dither enabled) to convert mp3s back to .wav - is the rippling still there when playing back the decoded .wavs?

FYI: If you successfully verified the problem by performing ABX tests - there's a sub-forum where you can upload short samples (> 30 sec., lossless compressed from the original, please).

Another thing to check is to make sure that the equalizer is off if you're using a program like winamp. An equalizer will artificially boost certain frequencies breaking the masking of noise that would normally not be heard or perceived.

Foobar2k did the trick. I was using Winamp.

Thanks for the help guys.