MP3Gain analyzes and losslessly adjusts mp3 files to a specified target volume.
It does not simply do peak amplitude normalization. Instead, it performs statistical analysis to determine how loud the file actually sounds to the human ear.
RECWAV gives a processor-efficient display of the spectrograph of an audio file, showing the energy in the sound at each moment and frequency. It was originally developed on a '286 under DOS and now also runs under Linux with svgalib.