Implementing audio effects using reverbs in C++

03 Oct 2023

Reverb is a popular audio effect that adds a sense of space and depth to a sound source. It simulates the reflections of sound in an acoustic environment, such as a room or a hall. In this blog post, we will explore how to implement reverbs in C++ and apply them to audio signals.

What is Reverb?

Reverb is a natural phenomenon that occurs when sound waves reflect off surfaces in an environment, reaching our ears multiple times with different time delays and amplitudes. It adds richness, warmth, and realism to audio recordings and enhances the listening experience. Reverberation can be created artificially using audio effects processors.

Implementing Reverb in C++

To implement reverbs in C++, we can use digital signal processing techniques. One common approach is to utilize the feedback delay network (FDN) algorithm, which emulates the behavior of sound reflections in an acoustic space.

Here’s a basic example code to implement a simple feedback delay network reverb in C++:

// Include necessary header files

#include <iostream>
#include <cmath>

// Define parameters

constexpr int numDelayLines = 4;
constexpr double roomSize = 0.5;
constexpr double feedbackGain = 0.6;

// Define delay line structure

struct DelayLine {
    int length;
    int writeIndex;
    double* buffer;
};

// Initialize delay line

void initDelayLine(DelayLine& delayLine, int length) {
    delayLine.length = length;
    delayLine.buffer = new double[length];
    std::fill_n(delayLine.buffer, length, 0.0);
    delayLine.writeIndex = 0;
}

// Process the audio signal with reverb

void processAudioWithReverb(double* audioBuffer, int bufferSize) {
    // Initialize delay lines
    DelayLine delayLines[numDelayLines];
    for (int i = 0; i < numDelayLines; i++) {
        int delay = static_cast<int>(roomSize * bufferSize * std::pow(0.8, i));
        initDelayLine(delayLines[i], delay);
    }
    
    // Process audio with reverb
    for (int i = 0; i < bufferSize; i++) {
        double wet = 0.0;
        double dry = audioBuffer[i];
        for (int j = 0; j < numDelayLines; j++) {
            int readIndex = (delayLines[j].writeIndex - delayLines[j].length + bufferSize) % bufferSize;
            wet += delayLines[j].buffer[readIndex];
            delayLines[j].buffer[delayLines[j].writeIndex] = dry + feedbackGain * wet;
            delayLines[j].writeIndex = (delayLines[j].writeIndex + 1) % bufferSize;
        }
        audioBuffer[i] = 0.5 * wet + dry;
    }
    
    // Cleanup delay lines
    for (int i = 0; i < numDelayLines; i++) {
        delete[] delayLines[i].buffer;
    }
}

int main() {
    // Load audio file or generate audio signal
    // Process audio with reverb using processAudioWithReverb() function
    // Save audio file or play audio signal
    
    return 0;
}

In the above code, we define a structure DelayLine to represent each delay line in the feedback delay network. We then initialize multiple delay lines with different delay lengths and process the audio signal by applying feedback and mixing the delayed signals together.

Conclusion

Implementing audio effects like reverbs in C++ allows us to enhance the quality and realism of audio recordings and simulations. By utilizing digital signal processing algorithms, such as the feedback delay network, we can recreate the behavior of sound reflections in different acoustic environments.

#audioeffects #reverb