Embedded Audio Visualization System

A real-time audio-reactive LED system built on an ESP32-S3. A microphone feeds live audio into an FFT pipeline that drives a 300-LED strip — soldered into a serpentine pattern to form a 15×20 pixel grid — through three switchable visualization modes, all running on dual FreeRTOS cores in parallel.

Features

• Beat-synced strobe — flashes the full grid white in time with detected beats, with a smooth brightness decay after each flash.
• Radial frequency map — renders concentric rings on the grid, each colored and brightened by the live energy in the bass, mid, or treble band.
• Lyric display — renders short text messages on the grid letter-by-letter using a custom 3×5 pixel bitmap font, advanced by a physical push button.
• Mode switching — cycle between the three modes with a physical button or serial command; a 16x2 I2C LCD shows the active mode.
• Ambient-light-aware brightness — an LDR sensor scales overall strip brightness to the room's ambient lighting.

Hardware

Component	Spec	Pin
LED strip	WS2812B, 300 LEDs, 15×20 serpentine grid	10
Microphone	MAX9814 (analog)	ADC 1
Ambient light sensor	LDR (analog)	ADC 5
Lyric advance button	Momentary, INPUT_PULLUP	6
Mode cycle button	Momentary, INPUT_PULLUP	42
LCD	16×2, I2C	SDA 11 / SCL 12
Microcontroller	ESP32-S3	—

Architecture

The system runs two FreeRTOS tasks pinned to separate cores, communicating through a shared SystemState struct (shared_state.h):

• Core 0 — audioTask: continuously samples the microphone (1024 samples @ ~20.5kHz), runs an FFT with Hann windowing, splits the spectrum into bass/mid/treble band energy, and runs beat detection on the bass band.
• Core 1 — LEDTask: reads ambient brightness, handles mode switching, and dispatches to whichever visualization mode is active, rendering to the LED strip and refreshing the LCD as needed.

Beat detection

Beat detection tracks a running average of bass-band energy (incremental mean, periodically reset so it re-adapts to volume/song changes) and flags a beat when the current bass energy exceeds that average by a tunable ratio — gated by a minimum interval derived from a max-BPM setting, so the detector can't fire faster than a musically plausible tempo allows.

This running-average + BPM-cooldown approach is adapted from blaz-r/ESP32-music-beat-sync. We had implemented our own normalized-min/max-range beat detector prior to adopting this approach; it's preserved (unused) in the code as KICK_THRESHOLD/KICK_MULTIPLIER.

Coordinate mapping

LED indices follow the strip's physical serpentine wiring. ledIndex(x, y) maps a logical Cartesian coordinate (origin at the bottom-left of the grid) to the correct physical LED index, accounting for the alternating left-to-right / right-to-left wiring direction of each row — this lets every visualization mode work in plain (x, y) grid coordinates instead of raw strip indices.

Controls

• Mode button (pin 42): cycles strobe → radial frequency map → lyrics → strobe.
• Lyric button (pin 6): advances to the next word (only active in lyrics mode).
• Serial: send 0, 1, or 2 over the serial monitor to jump directly to a mode.

Tuning

Key constants near the top of AudioReactiveLEDs.ino:

Constant	Purpose
LOW_FREQ_BIN / MID_FREQ_BIN	Band boundaries (Hz) for bass/mid/treble split
BEAT_MAX_BPM	Fastest tempo the beat detector will track
BEAT_MAG_RATIO	How far above the running average bass energy must spike to count as a beat
BEAT_AVG_COUNT_LIMIT / BEAT_AVG_COUNT_LOWER	Controls how quickly the running average re-adapts
BASS_DECAY_FACTOR	Strobe fade-out speed

Build

Built in the Arduino IDE for an ESP32-S3 board target (Tools → Board → ESP32 Dev Module family — not an AVR or mbed-based board).

Dependencies:

• arduinoFFT
• FastLED
• LiquidCrystal_I2C

File Structure

AudioReactiveLEDs/
├── AudioReactiveLEDs.ino   # main sketch: FFT, beat detection, LED rendering, tasks
└── shared_state.h          # SystemState struct shared between audio and LED cores