If you are really curious, here is a link to a piece about Best Digital Music Practices. It has some cool info about what the human ear can hear and why certain sampling rates and bit rates became standards.

http://www.bcr.org/cdp/best/digital-audio-bp.pdf

To your question about size vs. quality for MP3s for portable players, it some what depends what you will be listening to them on. If it is ear buds, then CBR 128kbps is plenty. If you are plugging them into a Bose Soundock or home Audio system then you may want to go a little higher. My suggestion would be to convert a few different tracks across a few genres and tempos at different bit rates and play them on whatever you are going to be listening to them on. Let your ears be the judge. If you can't tell the difference then use the higher compression.

I just believe that for your permanent archival copy, you should use a lossless format.

Hi thanks for the replies especially regarding the aac add on. I'm already ripping cds to flac for pc storage but its the getting the optimum sound quality/file size (if there is such a thing)for the mp3 player that i'm not sure of.
Regards

[quote="tykey"]Hello, new to mp3 and MM and need some advice please.
Have new Sony NWZ639 and have ripped a cd to my hd in flac, configured the player in auto conv with extra conversion choices of mp3 @extreme 256vbr or wma vbr but honestly I'm not sure what I'm doing.
What I'm looking for is the best trade off between sound quality/file size. The other thing is that the Sony supports aac (is this better than higher rate mp3/wma) but in the create conversion rules it isn't offered in the drop menu?
Any suggestions welcome.
Cheers[/quote]
for AAC encoding you need an add-on: http://www.mediamonkey.com/addons/input-output/

For the best quality in the smallest storage you can probably squeeze the most out of wma or aac files.

IMO, with the current price of disk storage, I don't know why if you were starting from scratch you wouldn't use a lossless format. While not supported by all players, I like FLAC. You can get files to about 60% of the full WAV file size with no loss of quality. I have 867 CDs ripped to FLAC with Moderate level 6 FLAC compression and the 12,144 tracks only take up 267GB. I like the fact the FLAC is an open format. If you are doing this with Monkey, you can always convert to a lossy format for portable players. There is a reasonably good overview of the various formats supported by Monkey in the Help - Contents - Introduction - Basic Concepts.

Hello, new to mp3 and MM and need some advice please.
Have new Sony NWZ639 and have ripped a cd to my hd in flac, configured the player in auto conv with extra conversion choices of mp3 @extreme 256vbr or wma vbr but honestly I'm not sure what I'm doing.
What I'm looking for is the best trade off between sound quality/file size. The other thing is that the Sony supports aac (is this better than higher rate mp3/wma) but in the create conversion rules it isn't offered in the drop menu?
Any suggestions welcome.
Cheers