ESP32 Bluetooth Polysynth & Sequencer

A versatile, real-time polyphonic synthesizer built for the ESP32, capable of streaming high-quality audio directly to Bluetooth speakers or headphones using the A2DP profile.

Features

• Polyphonic Synthesis: Play up to 8 notes simultaneously with independent envelope control.
• Wavetable Engine: Includes 4 classic waveforms: Sine, Triangle, Sawtooth, and Square.
• 3-Track Sequencer: Running Bass, Pad, and Lead patterns simultaneously with automated patch switching.
• Real-time FX & Modulation:
  • Pitch Shifting: Dynamic octave control via potentiometer.
  • LFO Modulation: Adjustable speed LFO controlling a resonant low-pass filter.
  • Reverb/Echo Engine: Integrated circular delay buffer for spatial depth.
• ADSR Envelopes: Smooth Attack and Release for every triggered note to prevent audio clicking.

---

Hardware Requirements

Pin Mapping (ESP32)

Component	Pin	Function
Note Buttons (x8)	4, 16, 17, 22, 18, 19, 21, 23	Note Triggers (C4 to C5)
Sequencer Button	14	Toggle Auto-Playback
Pitch Pot	35	Octave Selector (0.5x, 1x, 2x)
Waveform Pot	34	Waveform Selector (Sine, Tri, Saw, Square)
LFO Speed Pot	33	Filter Modulation Speed
Reverb Pot	32	Delay/Reverb Mix Level

---

Software & Libraries

This project relies on the following libraries:

• ESP32-A2DP by Phil Schatzmann.
• Standard Arduino ESP32 core.

Configuration

1. Change the BLUETOOTH_NAME variable in the code to match your target speaker/headphones:

   const char* BLUETOOTH_NAME = "Your Device Name";

Important: Ensure your ESP32 partition scheme supports Bluetooth (Select "Huge APP" or "No OTA" in the Arduino IDE Tools menu).

Technical Overview The Audio Engine The synth uses a Wavetable Synthesis approach. Instead of calculating expensive math functions in real-time for every sample, it reads pre-computed values from a 512-sample array.

The audio callback get_audio_data processes frames at 44.1kHz:

Mixing: It sums 8 independent oscillators.

Filtering: Applies a simple IIR Low-Pass Filter with a cutoff frequency modulated by a sine-wave LFO.

Spatial FX: The signal is fed into a Circular Delay Buffer (10,000 samples) to create a reverb/echo effect before clipping protection.

Installation

1. Clone this repository.

2. Install the ESP32-A2DP library in your Arduino IDE.

3. Select ESP32 Dev Module as your board.

4. Set Partition Scheme to Huge APP.

5. Upload the code and open the Serial Monitor (115200 baud).

6. Once "Bluetooth ON" appears, pair your device and start playing!