Archive for the ‘Code’ Category

In version two of solfa2sf: we can enter rhythm as well as pitch values, and we can control tempo and note decay

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Source Code for solfa2sf

The first version of solfa2sf took a string of solfa syllables and produced a .wav sound file representing it. This was good as a start, but we want to do more! In particular, we would like to be able to give different rhythm values to the notes. I’ve posted an improved version of solfa2sf that does just this. One can use the program on the command line like this

solfa2sf foo '| q do2 . e mi2 do2 . q sol sol |'

The result is a file foo.wav:


It represents a melody that starts with a quarter note C above middle C, continues with a pair of eighth notes, and ends with a pair of quarter notes.

To work with longer bits of music, it is best to write the solfa in a text editor, then compute the sound file like this.

solfa2sf -f theme.solfa

The file (theme.solfa) is this text below

| q do2 . e mi2 do2 . q sol sol |
| do2 . e mi2 do2 . q sol sol2 |
| e fa2 mi2 re2 do2 . ti do2 ti do2 |
| re2 do2 ti la . q sol x |

The symbols || . | have no effect on the program and could be omitted. They do help the human who reads or composes tis text, however. The possible rhythm values at this moment are w (whole note), h (half note) q (quarter note), e (eighth note), and s (sixteenth note). The command tempo:120 sets the tempo, and decay:0.1 determines how fast a note trails off into silence: Increase it to make the sound more sustained, decrease it to make it more percussive.

Below is the sound file. Click the link to play it. Do you recognize the piece? I studied it as a child back in Iceland.



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

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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


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.


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

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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:


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.


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A 440

We will use the magic of unix to make a tuning fork

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Things are a little slow at the shop these days – the aftermath of getting our big software development project done. With some time to spare, I’ve been reading The Audio Programming Book, edited by Richard Boulanger and Victor Lazzarini. As a substiture for note-taking as I work my way through this excellent text, I’ve to decided to blog about it.

The first task, from Chapter 1, around page 162, is to write a playable file for the sound of a tuning fork. The end result sounds like what you will hear if you click this link:


Wasn’t that nice? You did play it didn’t you? Here is how we did it – proceed only if you speak C and enjoy the power and elegance of Unix:

Step 1. Compile the program tfork.c using gcc tfork.c -o tfork. You will find it on the CD in chapters/01..., or here. Then execute this command:

./tfork tfork.txt 1.0 440.0 44100 0.2

The result is a 44,000 line text file, tfork.txt, whose first three lines are as follows:


It looks like this:

Tuning fork sound: A 440, exponential decay.

The file represents a sine wave at 440 Herz that decays exponentially to a small fraction of the starting amplitude after 1.0 seconds. The sample rate for the sound is 44100 Herz. The tfork command is used this way:

./tfork outfile duration frequency sample_rate decay_constant

Step 2. Compile the code in text2sf.c and install the binary somewhere in your search path. Execute the command

text2sf tfork.txt tfork.wav 44100 1 1.0

You now have a one-second CD-quality “recording” of a tuning fork! It is in the file tfork.wav You can play it using whatever means suits you and your computer best. On a mac, the command

play tfork.wav

works fine.

Isn’t it interesting that a sound can be represented so many different ways? As a list of numbers, that is, a text file. As an image. As the digital sound file that the computer can directly play. As vibrations in the air that tickle the hair cells in our inner ear. As a memory …

There must be some deep philosophical meaning in all this.


PS. Related links: Barry Threw: Art and Technology

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