SonicNet Audio Protocol

A low-latency, real-time audio streaming system built with Java and Netty. SonicNet implements a custom UDP-based protocol optimized for voice communication with adaptive jitter buffering and packet loss concealment.

Features

• Custom Binary Protocol: Efficient 24-byte header with sequence numbers and timestamps
• Adaptive Jitter Buffer: Dynamically adjusts to network conditions (3-10 packets)
• Packet Loss Concealment (PLC): Linear interpolation for smooth audio during packet loss
• Low Latency: ~50-100ms end-to-end latency
• High Performance: Non-blocking I/O with Netty framework
• Network Resilient: Handles up to 10% packet loss gracefully

Audio Configuration

• Sample Rate: 8 kHz (phone quality)
• Sample Size: 16-bit PCM
• Channels: Mono
• Frame Duration: 20ms (320 bytes/frame)
• Bandwidth: ~125 Kbps

Requirements

• Java 17 or higher
• Maven 3.6+
• Microphone and speakers/headphones

Quick Start

1. Build the Project

mvn clean compile

2. Run Receiver (Terminal 1)

mvn exec:java -Dexec.mainClass="com.sonicnet.AudioReceiver"

The receiver will start listening on port 9876.

3. Run Sender (Terminal 2)

mvn exec:java -Dexec.mainClass="com.sonicnet.AudioSenderRemote" \
  -Dexec.args="localhost 9876"

Speak into your microphone - you should hear yourself through the speakers with ~100ms delay.

Note: Use headphones to avoid feedback!

Project Structure

sonic-net/
├── src/main/java/com/sonicnet/
│   ├── protocol/              # Custom protocol implementation
│   │   ├── SonicNetPacket.java
│   │   ├── SonicNetPacketEncoder.java
│   │   └── SonicNetPacketDecoder.java
│   ├── buffer/                # Jitter buffer
│   │   └── JitterBuffer.java
│   ├── audio/                 # Audio capture/playback
│   │   ├── AudioConfig.java
│   │   ├── AudioCapture.java
│   │   └── AudioPlayback.java
│   ├── handler/               # Netty handlers
│   │   └── PacketHandler.java
│   ├── AudioReceiver.java     # Main receiver application
│   └── AudioSenderRemote.java # Main sender application
└── pom.xml

Testing

Loopback Test

Test audio capture and playback locally:

mvn exec:java -Dexec.mainClass="com.sonicnet.audio.AudioLoopbackTest"

Network Simulation

Test with simulated network conditions (latency, jitter, packet loss):

# Add 50ms delay + 10ms jitter + 2% packet loss
sudo tc qdisc add dev lo root netem delay 50ms 10ms loss 2%

# Run receiver and sender as usual

# Remove simulation when done
sudo tc qdisc del dev lo root

Remote Testing

Send audio to a remote host:

mvn exec:java -Dexec.mainClass="com.sonicnet.AudioSenderRemote" \
  -Dexec.args="<remote-host> 9876"

Performance

Typical Performance (localhost):

• Latency: 50-100ms
• Packet Loss: <2%
• Jitter: 2-5ms
• Buffer Size: 5-7 packets

Under Network Stress (50ms delay, 10ms jitter, 2% loss):

• Latency: 100-150ms
• Packet Loss: 2-3%
• Buffer adapts to 7-10 packets
• Audio quality: Good (PLC active)

Architecture

Protocol Design

Each packet contains:

• Magic Number: 0x534F4E49 ("SONI")
• Version: Protocol version (1)
• Sequence Number: Monotonically increasing
• Timestamp: Nanosecond precision
• Payload Length: Audio frame size
• Payload: Raw PCM audio data

Adaptive Jitter Buffer

The jitter buffer dynamically adjusts its size based on observed network jitter:

• Reorders out-of-order packets
• Detects and reports packet loss
• Adapts buffer size (3-10 packets) based on jitter
• Provides smooth playback despite network variations

Packet Loss Concealment

When packets are lost, the system uses linear interpolation between the last two received frames to generate smooth audio, minimizing audible artifacts.

Dependencies

• Netty 4.1.104: High-performance network framework
• Java Sound API: Audio capture and playback
• SLF4J + Logback: Logging

License

This project is for educational purposes.

Author

Built as a learning project to understand:

• UDP networking and real-time protocols
• Audio signal processing
• Adaptive buffering algorithms
• High-performance Java engineering