🛠 Chaîne audio 44,1 kHz : Audio Library, Design Tool, I2S, S/PDIF et sortie MQS

Objectives

The Teensy is the reference platform for DIY pedals and synths thanks to the Teensy Audio Library and its graphical Audio System Design Tool (https://www.pjrc.com/teensy/gui/): you draw a signal flow graph by drag-and-drop, and the tool EXPORTs functional Arduino code. The 600 MHz M7 and its DSP instructions enable real 44.1 kHz stereo. On the hardware side: 2 I2S/TDM ports (8 I2S channels / 16 TDM), independent S/PDIF inputs/outputs, and the MQS "Medium Quality Sound" output for direct speaker connection. Watch out for Audio Shield revisions: this is THE historical pitfall when moving from 3.x to 4.0.

Hardware

• 1 Teensy 4.0
• Choice of: Audio Shield (Rev D recommended — see below), PT8211 DAC kit (https://www.pjrc.com/store/pt8211_kit.html), or the MQS output on a pin
• Headphones or amplifier; Audio library (included in Teensyduino)

The Shield Revision Trap

Audio signals changed pins between Teensy 3.x and 4.0: the original Rev B shields do NOT work directly — you must add wires AND a 100 Ω series resistor on MCLK; Rev C only added the resistor; only Rev D natively routes the Teensy 4.0 (source: forum thread, Paul Stoffregen).

Complete Code (Generatable by the Design Tool)

// 440 Hz stéréo via l'Audio Shield — le graphe décrit ici est
// exactement ce que produit le Design Tool par glisser-déposer.
#include <Audio.h>
#include <Wire.h>
#include <SPI.h>

AudioSynthWaveformSine sine;
AudioOutputI2S         sortie;
AudioConnection        patchDroite(sine, 0, sortie, 0);
AudioConnection        patchGauche(sine, 0, sortie, 1);
AudioControlSGTL5000   codec;

void setup {
  AudioMemory(10);            // pool de blocs audio — sans lui, rien ne sort
  codec.enable;
  codec.volume(0.5);
  sine.frequency(440.0);
  sine.amplitude(0.3);
}

void loop { }   // tout tourne dans les interruptions audio

Expected Verification

A clean 440 Hz tone comes out in the headphones. Open the Design Tool: add an EffectReverb, an EffectFilterLowPass, a WAV file read from the SD card (the 8 SDIO pads on the back, SD.begin(BUILTIN_SDCARD)), export, and compare the generated code with yours — that is the whole point of the tool. Under load, check the remaining CPU headroom (the tool estimates the graph load): the M7 handles reverb + EQ + delay simultaneously.

Common Errors

• Forgetting AudioMemory(n): the code compiles, runs, and produces only polite silence — the block pool is mandatory.
• Plugging a Rev B shield "as on the Teensy 3.2": no sound or choppy sound — additional wiring + 100 Ω on MCLK are required; check the silkscreen on your shield.
• Believing the microphone input is connected to the internal ADC: the SGTL5000 codec on the Audio Shield goes through I2S; the edge ADC, on the other hand, is not meant for audio (~10 effective bits).
• Confusing MQS and I2S: MQS = filtered PWM output for a small speaker (decent quality, zero critical components); I2S = to a real DAC (PT8211, Audio Shield codec).
• Saturating the audio pool: each effect block costs; AudioMemory too small = crackling, too large = RAM starvation for the rest.
• S/PDIF: the input/output pins are independent of the I2S ports — do not configure them twice.