hello,

I was using and testing MPC Compression for a few weeks now and theres someting I'm wondering about.
On most tracks the bitrate is 160-180 which I would call normal. I noticed on some tracks the average bitrate is about 100 or even lower. If I tell the Winamp plugin to show the actual bitrate, it typically moves around 100 kbps. In fact I cannot hear any differences to the original anyway but as I could read in some threads mpc would not sound good at lower bitrates. is this an exception?

(the special example I'm talking about is the first track of the pulp fiction soundtrack "misirlou" from dick dale)

btw. I'm using standard quality (-no quality switch at all - only xlevel)

As far as I know, Musepack knows its business pretty well and if you can't hear any difference, it can probably be trusted. Anyway, if you are uncomfortable (as I am) with codecs going below certain threshold, you can use a higher preset, such as -q 5.5 or -q 6; but the effect is probably going to be just psychological.
Anyway, don't listen much to me. There are people far more knowledgeable out there who can give you a more precise answer.

If track is near-mono recording, you can try to add the --ms 15 switch.
But if the bitrate is low, enjoy it... quality is not affected.

It's normal that some tracks don't need high bitrates.
Normally though it will be the case of older recordings or very mono-like tracks.
In either case it's not a problem. If MPC didn't need more bits to encode the sample it was easy to encode. Nothing else; no need to do anything about it.

Sometimes at work I have to edit radio's commercial spots, then I save speechs recorded in mono in mpc format (--quality 5 --xlevel) and the bitrates is always lower than 100 kbs, almost 70-90 kbs, this is cool for me becouse I can hear any artifacts compared with the original wav files and the bitrate is slow too, around a half of mp3 LAME --alt-preset standard.

A better way to say this: "Musepack does not sound good at lower quality settings"

The quality settings are - as the name implies - quality settings. All files using the same setting will have the same quality, even though their bitrate may differ. The bitrate do not say anything about the perceptual quality of the file.