17. Sound synthesis & haptics 🔴

TTac ships no audio files. Every blip, chime and fanfare is synthesised at startup from oscillators (fx/Fx.kt), and every buzz is a vibration waveform.

Sound and vibration quick toggles, top right of the home screen — the app follows the same light/dark theme as this page

Digital audio in one paragraph

Sound is air pressure over time. Digitally, it's an array of numbers (samples), here 22,050 per second, each between −1 and 1 (stored as 16-bit integers). Playing a sound means handing that array to the audio hardware.

Oscillators

A tone at frequency f is a sine wave. Generating it sample by sample with a running phase lets the frequency change smoothly mid-note:

phase += 2π * freq / SAMPLE_RATE
val wave = if (triangle) (2 / π) * asin(sin(phase)) else sin(phase)

• Sine — pure and soft (✕ placements, chimes).
• Triangle — asin(sin(x)) bends a sine into straight ramps: brighter, a little "8-bit".
• Slides — interpolating freq from start to end across the note gives rising (✕) or falling (◯) chirps.

Envelopes

A raw oscillator starts and stops with a click. An envelope shapes volume over the note:

val env = min(1.0, t / 0.004) * exp(-4.2 * progress)   // 4 ms attack, exponential decay

A near-instant attack plus exponential decay is a pluck — the sound of a tapped glass or a marimba, which is what makes the UI feel physical.

Composing sounds from notes

Each effect is a list of notes with start times:

Effect	Recipe
Win	C–E–G–C arpeggio 90 ms apart, then a high E sparkle
Lose	two triangle notes, the second sliding down
Medal	a rising four-note fanfare plus two shimmering high notes
Blocks clear	two quick notes; a 4-line clear plays a five-note run

The notes are mixed by summing samples, then clamped to [−1, 1] and scaled to 80% to leave headroom.

Playback

Clips are rendered once (lazily) and played with AudioTrack in MODE_STATIC on a small thread pool, so overlapping sounds don't queue behind each other.

Haptics

Each sound has a matching VibrationEffect: tiny one-shots (8–22 ms) for taps and moves, waveforms for wins and medals (createWaveform(timings, amplitudes)), e.g. three rising pulses then a long buzz for a medal. Sound and haptics are toggled independently — also from quick controls on the home screen.

Going further

• Pre-rendering costs a few milliseconds and ~100 KB of memory once; synthesising per play would cost CPU at the worst moment (a win).
• For richer audio: ADSR envelopes, noise for percussion, or a low-pass filter (a one-pole IIR is two lines of code).