This example demonstrates scriptable effects: custom audio processors that transform the signal an AudioSource plays. A rack of small effects turns speech into radio chatter. It covers the following:
- A chain of effect components on a single
AudioSource, processed in component order, assembled at runtime, while the audio source plays. - Addressing one effect out of several with
AudioSource.GetEffectInstance, and bypassing it by disabling its component. - Filter coefficients derived from the audio configuration in
Configure, and rebuilt when the output device changes. - Data traveling out of the audio thread: the noise gate reports its envelope over the pipe, and the control part hands it back to the UI through a query message.
- A nested generator owned by an effect: the hiss effect creates a white noise generator, renders it into a scratch buffer from its own
Process, and destroys it when the effect goes away.
The project targets Unity 6.7 and is built on the scriptable audio pipeline APIs, specifically the part covered in the effects section.
Open the project in Unity 6.7, open Assets/Scenes/EffectRack.unity, and enter Play Mode.
The scene contains a single Radio GameObject holding an AudioSource with Count1To10.wav and the EffectRack panel, plus a camera that provides the AudioListener. The rack starts empty and the clip plays dry until you build one. A GUI panel appears:
- Playback starts stopped. Use the Play/Stop button. The clip loops by default.
- Bypass Effects takes every effect out at once, which is the quickest way to hear the dry clip.
- Each effect has an on/bypassed toggle and its own parameters. Everything is live: drag a slider while the clip plays and you hear it immediately.
- Handheld radio, Blown speaker and Spectrum only each clear the rack and rebuild it. They differ in what they contain and in what order, not just in their settings, so loading one is an audible teardown and rebuild rather than a parameter change. Clear empties the rack.
- Each effect row has ^ and v buttons that move it up/down the chain, and an x button that removes it mid-playback. The audio source rediscovers its effects when the components change, so the chain rebuilds while the clip keeps playing.
Effects run in the order their components were added, which the panel numbers top to bottom:
| Effect | What it does |
|---|---|
| Band pass | Rolls off everything outside a speech band, roughly 400 Hz to 2.6 kHz. |
| Drive | Pushes the signal into a soft clipper, for cheap transmitter distortion, then trims the output back down. |
| Noise gate | Silences the signal between phrases, and reports its envelope back for the meter. |
| Hiss | Mixes a bed of white noise under the signal, from a generator nested inside the effect. |
| Spectrum | Measures the signal without changing it, and reports the level in each of sixteen frequency bands for the panel to draw as a histogram. A bank of two-pole state-variable filters, not a transform. |
The implementation is in Assets/Scripts/. Each effect is one file holding the whole effect: the component, its real-time part, its control part, and the messages they exchange. The split follows the control vs realtime model described in the manual.
| File | Role |
|---|---|
Effects/BandPassEffect.cs |
Two one-pole filters. Shows coefficients computed on the control side, per-channel state allocated in Configure, and that state cleared when the device changes. |
Effects/DriveEffect.cs |
A stateless soft clipper with an output trim. The simplest complete effect here: no state, no allocation, and both parameters folded into one per-block multiply. |
Effects/NoiseGateEffect.cs |
An envelope follower and gate. Shows the pipe used in both directions, and a query message answered by writing into the caller's own message. |
Effects/HissEffect.cs |
A noise bed. Shows an effect owning a nested processor, and a scratch buffer allocated in Configure and released in Dispose. |
Effects/WhiteNoiseGenerator.cs |
The generator the hiss effect nests. Written exactly like a generator attached to an AudioSource. |
Effects/SpectrumEffect.cs |
A pass-through effect that measures. A filterbank keeps a reading down to sixteen numbers, which packs into one float4x4 and rides the pipe as a single message per block, so no shared memory is needed between the audio thread and the UI. |
EffectRack.cs |
The demo panel. Reads the chain back off the GameObject in component order, edits the effects while they play, and builds, reorders or clears the rack. Each preset is an ordered list of AddComponent calls, and a reorder rebuilds the chain from the swap onwards. |
Two rules shape all of the Process methods:
- Read the input sample before writing the output sample. When Unity runs an attached effect, the input and output buffers can reference the same memory.
- Write every output sample on every code path, including the paths that pass audio through untouched. The output buffer starts undefined, and Unity does not clear it.
This is meant as a teaching example. A few things are intentionally limited:
- One-pole filters: The band pass is two first-order sections, so its slopes are gentle. A real radio effect would use steeper filters, at the cost of a longer example.
- No parameter smoothing: Parameters jump to their new value when a message arrives. Dragging a slider fast can produce a small click. Production effects ramp between values across a buffer.
- Fixed channel budget: The band pass and the hiss effect size their buffers for eight channels, which covers every
AudioSpeakerMode. Anything wider passes through untouched. - Coarse spectrum: The analysis splits the signal into sixteen log-spaced bands, which is enough to see the band pass and the drive at work but far short of a transform. A real analyzer would use an FFT, at the cost of moving readings through shared memory rather than the pipe.
- Correlated noise: The hiss effect writes the same noise sample to every channel, so the static is mono. Decorrelated noise would need one random stream per channel.