In normal Linux distributions a special character device file /dev/dsp
is used from recording an playing sound. IF something is written into this file it will be played through the computer. lly we can record sound by reading from the device file. We can use the system calls open(), close(), read(), write() etc.. in this file. ioctl calls are used for controlling the sound card. Search for some documents about OSS (Open Sound Systems) in the net.
We ha a special library libsndfile for converting sound files in Linux. It may also help you a lot. See the http://www.mega-nerd.com/libsndfile/
for more details.