Sandsong

Sprinkle sand on a metal plate and play a tone through it, and the sand jumps away from the parts that move and settles on the lines that stay still. Each frequency draws its own figure. Sandsong turns that into an instrument: ten tone generators, binaural and isochronic modes, smooth glides between notes, and your own music mixed underneath.

You can say “set a tone” to Siri, speak commands that are understood on the device, and send the whole thing to a TV with AirPlay or Chromecast.

The sound comes from a shared C++17 engine with a plain C interface: a ten-voice bank, glide, binaural and isochronic modes, a look-ahead limiter and the voice-command grammar. On Apple devices it feeds AVAudioEngine directly. Android will call the same code, and the hardware runs it too.

Embedded chips have no double-precision maths, so the engine has a build option that swaps to a 32-bit fixed-point phase accumulator. That still gives a resolution of about 0.00001 Hz, a thousand times finer than the 0.01 Hz target. The tests cover precision, glide, the limiter and the protocol codec, and they run on any machine with a compiler.

The visuals are Metal. The plate's shape is a sum of its vibration modes, and a compute pass moves a million grains across it every frame: grains bounce where the plate moves and come to rest on the nodal lines, exactly as real sand does. A second mode draws Faraday waves on water. HDR bloom and tone mapping finish it.

The plate at the top of this page is a small WebGL version of the same model: 65,000 grains on a GPU, a tone from Web Audio, and the pitch tied to the mode.

Soma is the hardware family: an ESP32-S3 running the same engine, an I2S DAC and class-D amplifier, tactile transducers for felt bass, an exciter under a real Chladni plate, and a light ring. It talks to the app over a custom Bluetooth LE protocol with framing, authentication, clock sync and CRC checks. The codec is one allocation-free C file shared by the apps, the firmware and the website through WebAssembly.

The printable kit is generated from a single parametric script: every size is a named value, and the build refuses to export a part that is not one closed solid. You can turn the parts over below.

Frequency products are full of medical promises. Sandsong describes what a tone is associated with and keeps to relaxation, meditation and visualisation. The hardware plan leads with things you can actually feel, sound, vibration and light, rather than invisible fields.