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The Programs of the Week Star Wars Premiered

This Week’s Program: Dec 14 - Dec 18

Pardon this distraction from your Star Wars related festivities.

How to Make a Noise

You start with an oscillator. An oscillator produces a wave. When that wave is used to vibrate the speakers on a laptop, we hear sound. An oscillator can produce different shapes of waves, and the frequency and amplitude of that wave can result in different sounds.

In Overtone:

(definst foo [] (sin-osc 440))

This produces a SuperCollider Synth that when called as a function (eg. (foo)) produces the sound made by a sine wave with a frequency of 440 Hz. From the Overtone documentation:

Sine waves are often used for creating sub-basses or are mixed with other waveforms to add extra body or bottom end to a sound. They contain no harmonics and consist entirely of the fundamental frequency. This means that they’re not suitable for subtractive synthesis i.e. passing through filters such as a hpf or lpf. However, they are useful for additive synthesis i.e. adding multiple sine waves together at different frequencies, amplitudes and phase to create new timbres.

Subtractive synthesis is a method where the sound wave is modified by filter mechanisms. Additive synthesis is where waves are added together.

In Overtone there’s also sawtooth waves:

(definst bar [] (saw 440))

The sawtooth wave produces even and odd harmonics in series and therefore produces a bright sound that is an excellent starting point for brassy, raspy sounds. It’s also suitable for creating the gritty, bright sounds needed for leads and raspy basses. Due to its harmonic richness it’s extremely suitable for use with sounds that will be filter swept.

That means that sawtooth waves are suitable for subtractive synthesis.

An LFO is a secondary oscillator that produces a low-frequency signal used to modulate another signal. It could, for example, be used to modulate pitch, giving the effect of vibrato.

There’s a voltage-controlled oscillator, or VCO. There’s a voltage-controlled filter, or VCF. There’s a lot of these oscillators and filters in the music synthesis world, and I only have a rudimentary understanding of them.

The signals that I describe are patched together to create an instrument. This instrument is the Korg Monotron Analog Ribbon Synthesizer. It’s a super funky instrument. The schematics of the Monotron are publicly available and a fellow named Roger Allen made a Monotron in code for Overtone.

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Using Roger’s Monotron, I create a metronome and pass the two to a new play function. On each beat, I choose a random note from the C major scale and use Overtone’s ctl function to send a control message to the synthesizer to adjust the note. It plays in the REPL until I tell it to stop.

Here’s what that sounded like.

May the force be with you.

🖖 Mark