Arduino Mozzi Wilhelm Exercise

After completing a quick Mozzi exercise, I found a few problems that I wanted to fix in round 2.

The first problem was the use of audio clip from Portal 2. While Valve Software is unlikely to pursue legal action against a hobbyist exercise project for using one short sound from their game, they indisputably own the rights to that sound. If I wanted a short code exercise as any kind of example I can point people to, I should avoid using copyrighted work. Hunting around for a sound that would be recognizably popular but less unencumbered by copyright restrictions, I settled on the famous stock sound effect known as the Wilhelm scream. Information about this effect — as well as the sound clip itself — is found all over, making it a much better candidate.

The second problem was audible noise even when not playing sampled audio. Reading through Mozzi sound code and under-the-hood diagram I don’t understand why this noise is coming through. I explicitly wrote code to emit zero when there’s no sound, which I thought meant silence, but something else was happening that I don’t understand yet.

As a workaround, I will call stopMozzi() when playback ends, and when the button is pressed, I’ll call startMozzi(). The upside is that the noise between playback disappears, the downside is that I now have two very loud pops, one each at the start and end of playback. If connected to a powerful audio amplifier, this sudden impulse can destroy speakers. But I’ll be using it with a small battery-powered amplifier chip, so the destruction might not be as immediate. I would prefer to have neither the noise nor the pop, but until I figure out how, I would have to choose one of them. The decision today is for quick pops rather than ongoing noise.

This improved Arduino Mozzi exercise is publicly available on Github.

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