Minimizing file size


I use Audacity ( version 1.3.8 Unicode) on a Windows XP or Vista computer to record audio from a short wave communication receiver. The audio is a mono signal between 300 Hz and 3000 Hz. It is entered in the soundcard stereo input with only the left channel wired. During recording I see in the time-line window that the left and right channel is recorded. I am only interested in recording that left channel to reduce the size of the MP3 file which is created afterwards.
And I set the sample frequency to 11025 Hz to further reduce the file size.
How do I save only that channel to minimize the file size?

Thank you for your help.

You are warned against helping the MP3 compressor too much. Destructive compressors all work by assuming you are presenting them with a perfect, sharp, clear show and they do everything in their power to make sure as much quality as possible is preserved in the final show file. If you present them with a muffled, fuzzy, echoy show, guess what? The MP3 filesize is the same, but now you have a trashy show.

However, mono does help a lot. You can change audacity to mono in the preferences. Be sure to restart before you try to capture with the new settings.

You can rescue older stereo recordings by opening them up in Audacity and split the stereo channels with the controls on the left and then delete one of the two with the little [X]. Using the same tools, convert the one remaining track into mono. Recompress.

32-bit Floating would be a complete waste of time for you. Change to 16-bit in Audacity Preferences and restart.

You didn’t address the MP3 bitrate. Audacity 1.3.8 should ask you about compression bitrate as you export the show. You should be in the 32 range for your work and it may be possible to go even lower. If you’re still using the default 128 compression value, this will produce a much smaller file with very little damage.

If you’re not in love with MP3 (a technology designed in 1990), you can do much better with the more modern compressors AAC, M4A, MP4.