Looking for advice this time, not software
I need to prepare mp3s of speeches/presentations, recorded to wave with a high quality voice recorder. No matter what mp3 compression app I use, I'm finding that the lowest acceptable bitrate is 160 kbps. When I go below 160 kbps however, I'm getting a lot of artifacts in higher frequencies, the characteristic, infamous "underwater voice" distortion sound in mp3. The problem is that using 160 kbps yields files that are way too large for easy downloading (over 70 MB for a 60 minute recording).
At the same time I download a lot of podcasts which do not exhibit these artifacts, even though the bitrate used is 64 or even 32 kbps, and they have perfectly acceptable sound quality and definition. They typically fit 1 hour of speech in 20 MB or less. So what's the secret?
I'm guessing I should preprocess the wave file somehow, maybe use EQ to drop the high and low frequencies? Does anyone know what's the best way to go, or maybe there's a primer/how to for tnat sort of thing?