DSP · Wireless · ESP32 · Real-Time Audio

Digital
Walkie-Talkie

Full-duplex real-time voice communication between two ESP32 nodes over ESP-NOW — no router, no infrastructure. I2S digital microphone → frame segmentation → Spectral Subtraction + NLMS DSP chain → I2S amplifier output.

~4ms
TX Latency
8kHz
Sample Rate
~12dB
SNR Gain
~200m
Range
LEADER: Ahmed Abdulrazeq  |  TEAM: Islam Emad Ismail · Refaat Elsayed Refaat · Omar Tarek Elmaghawri · Omar Ahmed Desokey · Mohammed Reda Alasmar · Omar Alaa Zaghloul  |  SUPERVISOR: Dr. Rania Al-Abd
▶ DSP Simulation Hardware Diagram
Hardware Overview

Component Diagram

Both devices share the same hardware layout. The transmitter path goes through the microphone; the receiver path routes to the amplifier and speaker.

TRANSMITTER I2S MIC INMP441 Digital PDM I2S ESP32 TX NODE CPU WiFi Frame segmentation ESP-NOW TX 2.4GHz ANT External WIRELESS CHANNEL ESP-NOW Protocol 802.11 2.4GHz · No AP RECEIVER ANT External 2.4GHz ESP32 RX NODE DSP WiFi Spec.Sub + NLMS Audio reconstruct I2S AMP MAX98357 I2S Class D SPEAKER 4Ω 3W ① Capture ② Sample+Frame ③ Transmit ④ Wireless Hop ⑤ Receive ⑥ DSP Denoise ⑦ Output DSP CHAIN (RX NODE): ① Frame RX ESP-NOW ② Spectral Sub Stationary noise ③ NLMS Filter Adaptive noise ④ DAC / I2S Reconstruct ⑤ Speaker Clean audio out
ESP32 (×2)
Dual-core Xtensa LX6 · 240MHz · Built-in 2.4GHz WiFi chipset
I2S Microphone (INMP441)
Digital MEMS microphone · I2S PDM output · 24-bit · SNR 61dB
MAX98357A Amplifier
I2S input Class-D amp · 3.2W output · Single supply · No external components
External Antenna (×2)
2.4GHz directional antenna · SMA connector · ~4dBi gain · Extends range to ~200m
4Ω 3W Speaker
Full-range speaker driver matched to MAX98357A output
DSP Software (ESP32)
Spectral Subtraction + NLMS adaptive filter running bare-metal on core 1
Interactive Simulation

DSP Pipeline

Visualize how Spectral Subtraction and NLMS filtering clean the noisy audio signal in real time.

Audio Waveform Monitor LIVE
SNR: —
FREQUENCY SPECTRUM (0–4kHz)
Processing Chain — Latency Breakdown
① I2S Capture & Sampling ~0.125ms / frame
I2S DMA reads 16 samples from INMP441 at 8kHz. PDM to PCM decimation. 16-bit fixed-point buffer.
fs = 8000 Hz · frame = 16 samples · t_frame = 2ms
② ESP-NOW Transmission ~4ms
Frame packed as raw byte payload. ESP-NOW sends directly to MAC address — no AP, no DHCP, no IP overhead. One-way latency ≈ 4ms at 10m.
Protocol: IEEE 802.11 · Payload: 250 bytes max · Mode: Station
③ Spectral Subtraction ~6ms
FFT → estimate noise PSD in silence frames → subtract noise magnitude from signal magnitude → IFFT reconstruct. Removes stationary background noise (fan, HVAC).
|Ŝ(ω)| = |X(ω)| − α·|N̂(ω)| · ĉlamp to 0
④ NLMS Adaptive Filter ~3ms
Normalized Least Mean Squares adapts filter coefficients frame-by-frame to cancel dynamic noise (wind, movement). Converges in ~50ms after startup.
w(n+1) = w(n) + μ·e(n)·x(n) / (||x(n)||² + ε)
⑤ DAC / I2S Output ~2ms
Cleaned PCM samples streamed to MAX98357A via I2S. Class-D amplification to 4Ω speaker. Total pipeline: ~15ms end-to-end.
Total: 4ms (TX) + 9ms (DSP) + 2ms (DAC) = ~15ms
Technical Specifications

System Specs

📡
ESP-NOW Protocol
Peer-to-peer 802.11 protocol bypassing full WiFi stack. Sub-10ms latency without router.
Frequency2.4GHz IEEE 802.11
Max Payload250 bytes/frame
Latency~4ms @ 10m
Range (w/ ant)~200m LOS
AuthMAC pairing
🔊
Audio Chain
Digital audio path — no analog conversion until final output stage. Maximum SNR preservation.
Sample Rate8kHz (voice)
Bit Depth16-bit PCM
Frame Size16 samples
InterfaceI2S (full duplex)
SNR gain~12dB (DSP)
⚡
Hardware
Compact portable design. Low power consumption. Battery operable for field deployment.
MCUESP32 (×2 nodes)
MicrophoneINMP441 I2S MEMS
AmplifierMAX98357A I2S
Speaker4Ω 3W full-range
Power3.3V / 5V USB
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