Audio graph

The Teensy Audio design lives in audioinit.h: object declarations plus AudioConnection patch cords. Open it like a schematic.

High-level signal flow

flowchart LR
  subgraph samples [Samples 1-8]
    S[AudioPlayArrayResmp]
    SE[Envelope]
    SB[Bitcrusher]
    SF[Filter]
    SR[Freeverb]
  end

  subgraph poly [Poly synth ch11]
    PO[Oscillators]
    PM[Mix / ladder / env]
  end

  subgraph mono [Mono synths 13-14]
    MO[Oscillators]
    ME[Env / crush / filter / verb]
  end

  subgraph mix [Output]
    M1[mixer banks]
    END[mixer_end]
    COD[SGTL5000]
  end

  S --> SE --> SB --> SF --> SR --> M1
  PO --> PM --> M1
  MO --> ME --> M1
  M1 --> END --> COD

Exact node names differ per channel (sound1, envelope1, bitcrusher1, … and synth-side Swaveform*, Senvelope*, Sladder*).

Why some objects are EXTMEM

Large Audio objects and mixers are annotated EXTMEM so their state lives in PSRAM. That is a deliberate RAM1 conservation strategy — see Memory.

Custom nodes in src/

Component	Why it exists
resamplerReader.h	Variable-rate / interpolated playback beyond stock players
effect_freeverb_dmabuf	Freeverb buffers placed in DMAMEM for Teensy 4.1

toern.ino includes src/effect_freeverb_dmabuf.h and sets FASTLED_ALLOW_INTERRUPTS 0 so LED updates don’t fight the audio ISR world.

Changing the graph

1. Edit objects/connections in audioinit.h (Arduino Audio System Design Tool exports are a common starting point).
2. Update any pointers/arrays in filter/synth code that assume channel → object mapping.
3. Revisit mixer gain constants (GAIN_*, MIX_*) so summed voices don’t clip.
4. Test with multiple simultaneous sample hits + synths — headroom bugs show up under load, not silence.