A better way of creating .wav files given note data
Today’s post in my little saga of learning audio programming features a program quad.c. It creates a .wav file given a file of quadruples of the form (frequency in Hertz, duration in seconds, decay factor, amplitude). There are advantages of this approach as compared to to the previous one, which was based on concatenating the text files produced by tfork. First, only a single intermediate text file containing waveform sample data is created. In the first version, one file was created for each note, plus one for the concatenation of all the former. The concatenated file can be quite large. It is a file of 44,100 numbers for each second of audio which represents the sampled waveform. With quad, the file size is of corse the same as that of the concatenated file. The waveform which is sampled, however, has continuously varying phase. With the concatenated files produced by tfork, the phase begins at zero at the start of each note. More importantly, in the new version, the volume of the individual notes can be controlled by setting the amplitude in foo.quad. You will notice the increase in volume in note to note when you play the file foo.wav.
In the next post, quad will be incorporated in solfa2sf.
Example. Here is a three-line file of quadruples that represents the notes A E A’, where A’ is an octave above A = 220 Hertz:
220 1.0 0.5 0.2
330 1.0 0.5 0.5
440 1.0 0.5 1.0
The comments in quad.c give more details, but suffice to say here running the following plays the sound represented by foo.quad
./quad foo.quad foo.samp
text2sf foo.samp foo.wav 44100 1 .90
Note the increase in volume from note to note.