ABTEST

The ABTEST application was designed to be a small utility for comparing sound files. It plays WAV files, and lets you switch between them while they are playing. This makes it easy to hear the effects of MP3 encoding or other processing.
For example, encode a WAV file called "before.wav" into "128.mp3" at 128K, and into "256.mp3" at 256K. Then decode them back to "128.wav" and "256.wav". Using Winamp, you can decode by choosing Options/Preferences, Output tab, and setting the Output Device to WAV File Output.
Run ABTEST from the command prompt like this:
C:MP3>abtest before.wav 128.wav 256.wav
The music starts playing. Hit A to hear "before.wav", B to hear "128.wav",
and C to hear "256.wav". There is no interruption in the music when you
switch versions. You can easily hear any degradation produced by the encoder.
All the input files must have the same sampling rate (KHz), bits per sample
(8 or 16), and mono or stereo setting. To prevent interruptions in the sound, ABTEST does not close the audio port or interrupt the data flow when you switch files, so it cannot reset the playback parameters.