A song is a sequence of tones with different sequences and durations. The .freq files describe songs using pairs freq, msecs. For example the song "Happy Birthday" is described in the file songs/birthday.freq as:
1568 250
1568 187
1760 375
1568 375
2092 375
...
The program freq2wav
read a file.freq file passed as argument and generate a file file.wav with the frequency tones indicated by the file.freq file.
http://www.cs.purdue.edu/homes/grr/cs240/lab5-sound/
$ git clone https://github.com/lirongyuan/Music-Generator.git
$ make
$ ./freq2wav freq-file
$ ./testall