The sox program is a nice simple utility for converting audio data files from one format to another. After conversion, you can use many different audio editing utilities to modify the sound and use sox to convert the sound file back to your desired format. Using this for a telephony application, you have a wav file you have edited and you want to convert it back to 1 channel of 8000 samples/sec 16bit raw audio data:
sox -t wav recv0.wav -c 1 -r 8000 -s -w recv0.raw
The sox program is available under Ubuntu as an optional package. Adobe has a nice audio editing utility, but there are some good free ones as well. Two that I’ve used include Audacity and there is an audio studio program on Sourceforge. The audio studio program is a front end for sox and very simple, but it does the job for simple work.