Hello,
I have composed  a track using midi and audio sample loops, and have bounced the tracks to a wav file. In wav file the completed track sounds fine, but when I convert it to mp3, there is degradation in sound quality. I have composed other tracks before, not with sample loops, but this has never been an issue. I have tried different bitrates to see if this improves quality, but it does not. Any help would be appreciated. Thanks.  

MP3s are compressed and so will be a loss of fidelity, but its usually not all that noticeable unless you have really good ears. What bit rates are you using? 128 is the minimum for almost CD quality sound. 192, 256 and 320 are successively better, but the file gets incrementally larger with each. The way MP3 compress the sound is by removing the data at frequencies outside the normal hearing range so maybe your tracks have an unusually large frequency range that the MP3 cannot handle. 

If your using Sonar and exporting as an mp3, try moving the slider over to best quality. As stated above, a higher bitrate will get you better results.

It may be that your wav file to too loud. You might want to try exporting a wav with a little more headroom for the mp3 converter to work with.

DIto what scook just said:

http://www.about-audio-ma...mastering-for-mp3.html