Implementing audio effects in real-time with C++

03 Oct 2023

Audio effects play an important role in enhancing the audio quality and creating an immersive experience for users. Real-time audio effects are particularly useful in applications such as music production, gaming, and audio streaming. In this blog post, we will explore how to implement audio effects in real-time using C++.

Understanding Real-Time Audio Processing

Real-time audio processing involves applying audio effects to the input audio signal and generating the processed audio output in real-time with minimal latency. This is crucial for applications where low latency is a priority, such as live performances or interactive audio applications.

Basic Steps for Implementing Audio Effects

To implement audio effects in real-time using C++, we can follow these basic steps:

Audio Input: Start by capturing the audio input from a microphone or an audio file. Use a library like PortAudio, RtAudio, or libsoundio to handle audio input/output.

// C++ code example for capturing audio input using PortAudio
#include <portaudio.h>

// Callback function for processing audio input
int audioInputCallback(const void* inputBuffer, void* outputBuffer,
                       unsigned long framesPerBuffer,
                       const PaStreamCallbackTimeInfo* timeInfo,
                       PaStreamCallbackFlags statusFlags,
                       void* userData) {
    // Process audio input here
    return paContinue;
}

int main() {
    PaStream* stream;
    Pa_Initialize();

    // Open an audio stream for capturing audio input
    Pa_OpenDefaultStream(&stream, 1, 0, paFloat32, 44100, 256,
                         audioInputCallback, NULL);

    // Start capturing audio input
    Pa_StartStream(stream);

    // Keep the program running while capturing audio
    while (/* some condition */) {
        // Handle other tasks or wait for input
    }

    // Stop capturing audio and clean up
    Pa_StopStream(stream);
    Pa_CloseStream(stream);
    Pa_Terminate();

    return 0;
}

Apply Audio Effects: Once we have the audio input, we can apply various audio effects to the input signal. There are several types of audio effects, such as equalizers, reverb, delay, chorus, and more. Each effect has its own algorithms and parameters, which can be adjusted to achieve the desired sound enhancement.

// C++ code example for applying an audio effect (delay)
#include <vector>

// Delay effect parameters
const int delayBufferSize = 44100 * 2; // Store 2 seconds of audio samples
const int delayTime = 5000; // Delay time in milliseconds

class DelayEffect {
private:
    std::vector<float> delayBuffer;
    int writePosition;

public:
    DelayEffect() : delayBuffer(delayBufferSize), writePosition(0) {}

    void process(std::vector<float>& audioSamples) {
        for (auto& sample : audioSamples) {
            float delayedSample = delayBuffer[writePosition];

            // Mix delayed sample with current sample
            sample = sample + delayedSample;

            // Write current sample into the delay buffer
            delayBuffer[writePosition] = sample;

            // Increment the write position and wrap around
            writePosition = (writePosition + 1) % delayBufferSize;
        }
    }
};

Audio Output: Finally, we need to output the processed audio signal to a destination such as speakers, headphones, or an audio file. Similar to audio input, we can use a library like PortAudio, RtAudio, or libsoundio to handle audio output.

// C++ code example for outputting audio using PortAudio
#include <portaudio.h>

// Callback function for audio output
int audioOutputCallback(const void* inputBuffer, void* outputBuffer,
                        unsigned long framesPerBuffer,
                        const PaStreamCallbackTimeInfo* timeInfo,
                        PaStreamCallbackFlags statusFlags,
                        void* userData) {
    // Copy processed audio to output buffer
    std::vector<float>& audioOutput = *static_cast<std::vector<float>*>(userData);
    std::memcpy(outputBuffer, audioOutput.data(), framesPerBuffer * sizeof(float));

    return paContinue;
}

int main() {
    PaStream* stream;
    Pa_Initialize();

    // Open an audio stream for audio output
    Pa_OpenDefaultStream(&stream, 0, 1, paFloat32, 44100, 256,
                         audioOutputCallback, &audioOutput);

    // Start the audio output stream
    Pa_StartStream(stream);

    // Keep the program running while playing audio
    while (/* some condition */) {
        // Handle other tasks or user input
    }

    // Stop the audio output stream and clean up
    Pa_StopStream(stream);
    Pa_CloseStream(stream);
    Pa_Terminate();

    return 0;
}

Wrapping Up

Implementing audio effects in real-time with C++ allows us to create dynamic and interactive audio applications. By capturing audio input, applying effects, and outputting the processed audio signal, we can create immersive audio experiences for users.

Remember, the examples provided in this blog post are simplified to illustrate the basic implementation steps. In a real-world scenario, you may need to handle buffer management, parameter control, and other optimizations to achieve optimal performance.

Keep exploring different audio effects and algorithms to add depth and richness to your audio applications. Happy coding!

#C++ #RealTimeAudioEffects