Audacity Forum

Hi all,

I'm a complete noob with Audacity so pardon the dumb questions.

I have a large library of MP3 Podcasts and not enough time to listen to them so I would like to speed them up in bulk, preserving them but also obtaining the smallest file size possible.

The time it takes isn't particularly an issue for me, I'll probably process one folder at a time so it doesn't matter to me if it takes ages, I will just download all the episodes available at a given time, and process them away!

It seems that to get the best out of LAME I would want to use cmd line instructions but I can't seem to use them with the way you have to Export with the chains.

Can someone provide some guidance on how I would achieve optimal quality for voice sources while using the speedup chains?

Any help would be greatly appreciated.

Thanks,

For best quality, don't change them at all, just play them back faster when you want to listen to them.

steve wrote:For best quality, don't change them at all, just play them back faster when you want to listen to them.

Should have mentioned I listen to them in an ipod in my car, and it cannot speed up mp3, only Audiobooks in MP4 format.

There is always some loss of sound quality when encoding in any lossy compressed format such as MP3.
Audacity can only work with uncompressed audio data, so when editing an MP3 Audacity will decode the MP3 first and then if you export as MP3 after editing there will be some loss of sound quality. The loss of sound quality is cumulative and unrecoverable. Each time it is encoded there will be additional sound quality loss.

The degree of sound quality degrading can be limited by using a high bit-rate, but this increases the file size, so you need to make a trade-off between file size and sound quality.

VBR encoding will generally produce better sound quality for a similar file size than CBR.
If the audio track in Audacity is mono then lower bit rates can be used while still getting acceptable sound quality.
Try using mono tracks and the lowest VBR bit rate (45-85 kbps) and see if the sound quality is good enough.
if it sounds too poor, go up to the next lowest VBR setting.
If you want to try even small file sizes (and lower sound quality) try the low bit-rate settings tat are available with "Average" bit rate mode enabled.

The standard encoding options are highly optimised and although additional options are available through command line options you are unlikely to be able to make significant improvements over the options available through the normal Audacity interface.

steve wrote:The standard encoding options are highly optimised and although additional options are available through command line options you are unlikely to be able to make significant improvements over the options available through the normal Audacity interface.

Thanks Steve, this is good advice, perhaps I am overcomplicating something that should be simple

Even with only the options in the Audacity 1.3 interface, there are still a lot of options, so it's worth experimenting.