sox stands for Sound EXchange. And it is doubtless the most capable audio processing command line utility. Its power sometimes cannot be matched even by expensive DAWs with fancy graphics and high price tags.

In the traidition of UNIX simplicity sox does exactly what you want without having to resort to extra gymnastics like viewing the waveform or loading a GUI interface. Its power is as amazing as its speed.

You should read the manual page of sox(1) as well as soxexam(1) which is a marvellous intro to "audio effects". I tried some of them and was dumb founded how much one could do with the UNIX command line...

The default sox install cannot process mp3 files. So you have to first convert it into wav format or some other format sox understands.

This is no big deal as mpg321 or ffmpeg can help you.

$ ffmpeg -i song.mp3 song.wav

Now that you have the raw wav file, the fun begins .

Is it a boring lecture by your professor that puts you to sleep?

No problem. Just enliven it with a few echo effects.

 $play lecture.wav echo 0.5 0.6 60 1

Oops! Forgot to mention that "play" is a companion program to sox and all of sox's effects can be used with play. Once you are satisfied with the result, you can write out the audio file with sox.For instance, if you want to lecture to have echo, just do this.

$ sox lecture.wav echo-lecture.wav 0.5 0.6 60 1

You can do low pass filtering, band pass filtering, high pass filtering, amplify, attenuate and process the audio file in multifarious ways. All with intuitive command lines.

$ play music.wav lowpass 1500

$ play music.wav highpass 3500 lowpass 200

#This amplifies by 5 times
# Be careful, this may lead to clipping...
$ play music.wav vol 5

$ play file.wav reverb 1.0 400.0 380.0

$ play file.wav stretch 2

It also is a mixer and you can combine multiple audio tracks by simply passing them on the command line.

One useful thing to do would be to split an mp3 file or remove unnecessary parts. You can just convert it into wav format.Then use sox for the splitting and re encode it with bladeenc or toolame.I used audacity for this as it gave me fine grained control with its zoom feature. But this is not something sox cannot do of course.

You can combine sox into a UNIX pipeline for certain interesting effects. You can record voice from a microphone directly into sox and save it into a different format or add effects on the fly.

The easy scriptability of sox lends easily into cron jobs. You are limited only by your imagination as is always the case with UNIX.