trouble compressing a mp3 speech

On other speeches (1 person speaking for an hour) I use LAME to compress like this:

lame -m m -b 24 --resample 22.05 -f input.wav output.mp3

This works fine and produces no static.  I am now trying to take huge 35 MB mp3 files and compress them.  They were previously encoded at a frequency
of 44.1 and a bitrate of 192 KHz.  The files are 1 speaker with a single acoustic guitar intro.  I'm using the previous command with --mp3input and
getting static.  

What am I doing wrong?

Marty