Cpp-Audio-Bitcrusher 🎛️

A high-performance, lo-fi audio effect tool built from scratch in C++. This project demonstrates Systems Programming concepts including binary file manipulation, memory mapping, and digital signal processing (DSP) without relying on external audio libraries like libsndfile or JUCE.

🎧 Audio Demo

Hear the effect in action. The tool reduces both the bit depth (resolution) and sample rate (frequency) to create a retro, robotic, or "broken" sound.

Description	Audio File
Original Vocal (Clean 16-bit PCM)	▶️ Play Original
Bitcrushed (8-bit equivalent, 4x downsample)	▶️ Play Bitcrushed

Note: Click the links above to play the WAV files directly in your browser.

✨ Features

• No Dependencies: Standard C++ Standard Library (<vector>, <fstream>, <cstdint>) only.
• Binary WAV Parsing: Custom implementation of the WAV file specification (RIFF/WAVE header parsing).
• Tunable Destruction:
  • Bit Depth Reduction: Integer quantization simulating 8-bit, 4-bit, or even 1-bit audio.
  • Sample Rate Decimation: Sample-and-hold algorithm to introduce metallic aliasing artifacts.
• High Performance: Direct memory manipulation of PCM data.

🛠️ Build & Run

Prerequisites

• C++ Compiler (GCC/MinGW)
• Make (or mingw32-make on Windows)

Compilation

make

(On Windows with MinGW, use mingw32-make)

Usage

./bitcrusher <input.wav> <output.wav> [crush_factor] [downsample_factor]

• input.wav: Source PCM WAV file.
• output.wav: Destination file.
• crush_factor: Quantization intensity (default: 256). Higher = more distorted.
• downsample_factor: Sample rate reduction (default: 1). Higher = more robotic/metallic.

Example Commands

1. The "Retro Game" Sound (Recommended)

./bitcrusher samples/demo_original.wav samples/out_retro.wav 256 4

Simulates ~8-bit hardware running at ~11kHz.

2. Modern Lo-Fi

./bitcrusher samples/demo_original.wav samples/out_lofi.wav 64 2

Subtle digitization.

3. Total Destruction

./bitcrusher samples/demo_original.wav samples/out_broken.wav 1024 16

Unintelligible digital noise.

🧠 How It Works

1. The Binary Reader

Instead of using a library, we define the WAV header struct manually to match the binary layout of the WAV file format:

struct WavHeader {
    char riff[4];                // "RIFF"
    uint32_t overall_size;       // File size
    // ... exact 44-byte mapping ...
};

We use std::ifstream in binary mode to map these bytes directly into memory.

2. The Bitcrushing Logic

The distortion is achieved through integer math. By defining a reductionFactor (e.g., 256), we perform integer division to truncate the signal's precision, then multiply back to scale it.

// Integer Division drops the remainder (Quantization)
sample = (sample / factor) * factor;

3. Sample Rate Decimation

To simulate a lower sample rate (which causes the characteristic "ringing"), we implement a Sample-and-Hold algorithm. We update the output signal only every N samples, holding the previous value in between.

if (i % downsample == 0) {
    current_sample = input_data[i]; // Sample
}
output_data[i] = current_sample;    // Hold

📄 License

This project is open source and available under the MIT License.