Bitrate Conversion

[jerryds]

I have original music at 320 and when I edited the songs I exported at 128. Can I change the already exported files back to 320? Or should I start over with the original songs and export them at 320?

[steve]

The lower the bit rate, the worse the audio quality.
Each time the audio is encoded in a lossy format (such as MP3, AAC, OGG, etc) some of the audio information is discarded, which causes a loss in sound quality. The higher the compression, the lower the bit rate and smaller the file size is, but also, the worse the sound quality. These losses are not recoverable.

Ideally you should work with uncompressed data (WAV, AIFF etc).
If you must work from an MP3, it's better to work from the highest quality MP3 that you have available (the closest to the original uncompressed source material) which will be your original 320 kbps MP3. Converting from 128 kbps to 320 kbps will not improve the quality - the file size will increase, but the conversion will still cause the quality to get worse.

[jerryds]

Thanks for the quick response Steve, I'm using the songs for music to an MP3 player with regular earphones. I've read on the net that since I'm using basic earphones the higher bitrate would make no difference in the quality of the sound. Is this true?

[steve]

When I listen to music on my laptop speakers, I can hardly ell the difference between 64kbps MP3 and the original WAV file.
When listening through good speakers or headphones, I find anything worse than about 192 kbps intensely irritating.

Converting from 320 kbps to 128 kbps will be (a bit) worse than converting from WAV (uncompressed) to 128 kbps.
Converting from 320 kbps to 128 kbps to 320 kbps will be worse than converting from 320 kbps to 128 kbps.

My recommendation would be to always work from the highest quality version that you have available, and always keep a high quality backup copy.
If you're happy listening to a 128 kbps version while out jogging and it means that you get a few more songs on your MP3 player, then there's nothing wrong with that. If you have a high quality backup, then you can always make a direct copy from that if ever you want a higher than 128 kbps version. What you can't do is to make a better quality version from a low quality version - MP3 encoding always looses some sound quality and the loss is not recoverable.