Compressing Voice with MP3

I'm looking to compress some lectures which are in MP3 format. Currently, they're each about 75开发者_StackOverflow社区MB and I'm looking to compress them a lot. Can anyone suggest some good encoding options for LAME to get decent quality and small filesize?

I think the files are in stereo, but obviously they could be bounced down to mono if need be. Is there a guide for compressing just voice in MP3 efficiently?

http://macintoshhowto.com/audio/how-to-compress-speech.html has this:

1. SMALLEST FILE SIZE ACCEPTABLE QUALITY. For very small file size (4MB for 20 minutes) and acceptable quality, use the LAME encoder (the the separate article on Itunes songs to find out about the LAME encoder) with the following arguments in the ‘Encoding options’ Box:

   -V 9 --vbr-new -mm -h -q 0
   

2. An even better option than above but slightly more complicated is: Firstly convert the file to 22khz sample rate and mono, (eg in Audacity) then use the following LAME settings:

   -V 8 --vbr-new -h -q 0
   

3. BETTER QUALITY AND ACCEPTABLE FILE SIZE. For about twice the size files (8MB for 20 minutes of speech) but very very good quality try this in LAME encoder:

   --preset voice
   

OR

-V 8 --vbr-new -h -q 0