Audio effects play a crucial role in enhancing the quality and clarity of audio recordings. One of the commonly used audio effects is compression, which helps in controlling the dynamic range of an audio signal. In this blog post, we will explore how to implement audio compression using compressors in C++.

Understanding Compression

Compression is a technique that reduces the difference between the loudest and softest parts of an audio signal. It achieves this by automatically reducing the gain of the audio signal when it exceeds a certain threshold level. This ensures that the overall volume stays within a desired range.

Implementing a Compressor in C++

To implement a compressor in C++, we need to understand the basic steps involved:

1. Envelope Detection: The first step is to calculate the envelope of the audio signal, which represents the amplitude variations over time. This can be done using the Root Mean Square (RMS) algorithm. The RMS value of a signal is calculated by taking the square root of the mean of the squared values of the signal samples over a small duration.

2. Thresholding: Once we have the envelope, we compare it with a predefined threshold level. If the envelope exceeds the threshold, we apply compression; otherwise, we leave the signal unchanged.

3. Compression Ratio: The compression ratio determines the amount of gain reduction applied to the signal when it exceeds the threshold. A higher compression ratio means more gain reduction.

4. Applying Gain Reduction: To apply gain reduction, we multiply the audio signal by the inverse of the compression ratio. This effectively reduces the amplitude of the signal when it exceeds the threshold.

5. Make-up Gain: Since compression reduces the overall volume of the signal, we need to compensate for this reduction by applying a make-up gain. The make-up gain amplifies the compressed signal to achieve the desired output volume.

Example Code

Let’s take a look at a sample implementation of a compressor in C++:

#include <iostream>
#include <cmath>

double calculateRMS(double* signal, int length) {
    double sum = 0.0;
    for (int i = 0; i < length; i++) {
        sum += signal[i] * signal[i];
    }
    double meanSquared = sum / length;
    return sqrt(meanSquared);
}

void applyCompression(double* signal, int length, double threshold, double ratio, double makeupGain) {
    double envelope = calculateRMS(signal, length);
    
    if (envelope > threshold) {
        double gainReduction = (envelope - threshold) * (1 - 1 / ratio);
        for (int i = 0; i < length; i++) {
            signal[i] *= 1 / (1 + gainReduction);
        }
    }
    
    for (int i = 0; i < length; i++) {
        signal[i] *= makeupGain;
    }
}

int main() {
    // Example usage
    const int bufferSize = 100;
    double audioSignal[bufferSize] = { /* Audio samples here */ };
    
    double threshold = 0.7; // Set your desired threshold level
    double ratio = 2.0; // Set your desired compression ratio
    double makeupGain = 1.5; // Set your desired makeup gain
    
    applyCompression(audioSignal, bufferSize, threshold, ratio, makeupGain);
    
    // Rest of your code...
    
    return 0;
}

In the above code, we have defined a calculateRMS function to calculate the RMS value of the signal and an applyCompression function to apply compression to the signal. The main function demonstrates how to use the compressor by setting the desired threshold, ratio, and makeup gain.

Conclusion

By implementing compressors in C++, you can add audio compression as an effect in your audio processing applications. This can help in achieving a more balanced and controlled audio output, improving the overall listening experience.

Remember to experiment with different threshold levels, compression ratios, and makeup gains to achieve the desired audio effect for your specific application.

#coding #audioeffects