Audio Programming 3: From Solfa to Sound

We combine C and Python programming to transform a sequence of solfege syllables, e.g., do re mi re do, into a sound file.

1 | 2 | 3 | 4 | 5 | Source Code

In our last post we used tfork and a few unix commands to construct a sound file for an A major chord, A C# E A’. The idea was (1) to make text files representing the sounds of the individual notes using tfork, (2) glue the text files end-to-end using cat, (3) convert the resulting big text file into a .wav file using text2sf.

This works fine for short “melodies,” but it soon gets tedious — and out of hand. A better way is to write a short program that does all this for you, given a text string of solfa syllables like “do re mi re do”. This is what we do in the Python program solfa2sf. Below is the sound produced by


./solfa2sf -w foo 0.3 0.1 do re mi re do


SOUND OF FOO

SOURCE CODE for solfa2sf

In running solfa2sf, the arguments are as follows: (1) an option: -d for “dry run”, i.e., no output, -v for an output file with verbose messages, -w for wet, the opposite of dry: produces the output .wav file with few messages; (2) the file name; foo results in an output file foo.wav, (3) the note duration in seconds, (4) the decay time, (*) the solfa syllables.

If you use a small decay time, the sound is percussive, like a marimba, or even a drum. If you use a large one, it is more like an organ. Try delay times of 0.01, 0.1, and 1.0 to see what the effect is.

Python is very good with strings, lists, and dictionaries, which is what we need to parse and handle an input string like “do re mi re do’. C is the best tool for fast computation. So we use them together! As you can see from the source code, we call on the C program tfork using the Python command os.system. Like a carpenter, we use saw, chisel, hammer, etc. as needed for the task at hand.

HH

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Audio Programming 2: Constructing a Chord

We combine the power of tfork and text2sf with the magic of unix to construct a sound file for an A major chord.

1 | 2 | 3 | 4 | 5 | Source Code

A Chord

In Audio Programming 1, we compiled the tfork.c program in chapter 1 of the Audio Programming Book, Richard Boulanger and Victor Lazzarini, editors. This program , together with text2sf, gave us the tools needed to algorithmically construct simple sounds, namely an exponentially decaying sine wave. We used these tools to fabricate a file that represents the sound of a tuning fork.

Simple as these two tools are, they gives us the means to construct more complicated sounds without any additional C programming (fun though that is!). We will use the magic of unix. To begin, a short shell script:


# Language: unix/sh
# File: sound.sh
# Example: sh sound.sh 440 a --- writes text representation of
# a 0.2 second 220 Herz sound to a file a.txt

./tfork $2.txt 0.2 $1 44100 0.2


Using sound.sh, we make four sounds, each 0.2 seconds in duration, with frequencies of 220, 275, 330, and 440 Hertz. These correspond to the notes A, C#, E, and A’ = A one octave higher. The frequency ratios are C#/A = 5/4, E/A = 3/2, and A’/A = 2. Thus we are using Pythagorean tuning, in which pitch ratios in the scale are rational numbers with small numerator and denominator.

Let us now execute the following commands:


% sh sound.sh 220 a
% sh sound.sh 275 c#
% sh sound.sh 330 e
% sh sounds.sh 440 a2


The result is the creation of text files a.txt, c#.txt, etc., which represent the given sounds. Next, we concatenate these files, putting a.txt first, c#.txt next, etc:


% cat a.txt c#.txt e.txt a2.txt >chord.txt


Then, we convert chord.txt into a .wav file:


% text2sf chord.txt chord.wav 44100 1 1.0


To conclude, we play the file:


play chord.wav


Here is the sound:

A MAJOR CHORD

Clearly there is more to do, among which are  (1) Clean up this sound: it needs to fade cleanly into silence; (2) Develop a mini language for transforming a sequence of pitch names into a sound file; (3) make more complex sounds.

HH

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