OK first off I can not hear any difference above 224 CBR, And my level of frequency hearing is about 16000KHz

If I use a 16500 lowpass filter on 192 CBR will I get an increase in quality as apposed to using a higher lowpass of say 18500? I am using Lame 3.98 v2

-b 192 -h --lowpass 16500

Now when I rip 192 CBR with a lowpass of 16500, I really don't see any drop in file size for say when I use a 18500 lowpass filter so I am assuming it is using the extra bits for better quality? I know Joint Stereo increases quality, so does lowpass do the same? or does it actually screw things up somehow going this low? I know the bits saved from the lowpass must be going somewhere.

You won't see any difference in bitrate with CBR because it's constant bitrate (hence the name), although lowpass filtering at a lower frequency than the default may increase perceived quality due to the reduced complexity of the signal being fed to the encoder.

Regardless, I'd still be inclined to leave everything at default personally, and for the best ratio of bitrate to quality, use VBR. That's what it's there for.

Cheers, Slipstreem.

If thats the case then where do the bits go? I mean the file size does not change yet the upper frequency is chopped off, those bits must go somewhere.

Check it out, encode a 192 CBR with a 19000 lowpass and one with a 16000 lowpass, the file size stays basically the same so the bits saved on the 16000 lowpass must go somewhere?

Q) Can a lowpass with MP3 improve quality?
A) Yes, due to the design of MP3 as a format, the higher frequencies can be difficult to encode, so reducing them prevents this effect.

Q) On a CBR encode, where do the "extra bits" go?
A) Several possibilities:
- Less optimal loop choosen.
- Padding (i.e. empty data)
- Increase of quality.

Nothing guarantees it is the third. Nothing guaranteees it is not.