Audio spatialization is the process of creating a three-dimensional sound experience, where sounds are positioned in a virtual space to give the listener a sense of direction and depth. This technique is widely used in various applications, including virtual reality, gaming, and immersive audio experiences. In this blog post, we will explore some popular audio spatialization techniques implemented in C++.

1. HRTF (Head-Related Transfer Function)

The Head-Related Transfer Function technique simulates the way sound waves interact with the human head and ears to create positional audio cues. It takes into account the shape of the listener’s head, the position of the sound source, and the listener’s ear canal shape to produce an accurate spatial audio representation.

HRTF-based spatialization libraries, such as SOFA (Spatially Oriented Format for Acoustics), provide a collection of personalized HRTF measurements that can be used to spatialize audio in real-time. These libraries typically provide functions to interpolate HRTFs based on the listener’s position in the virtual space.

Example code using the SOFA library for HRTF-based spatialization:

#include <sofa.h>

// Initialize the SOFA library with the listener's personalized HRTF measurements
SOFA::initialize("path/to/HRTF.sofa");

// Set the listener's position in the virtual space
SOFA::setListenerPosition(x, y, z);

// Set the position of the sound source
SOFA::setSourcePosition(x, y, z);

// Retrieve and apply the HRTF filters for spatializing the audio
float leftEarFilter[FFT_SIZE];  // Filter coefficients for the left ear
float rightEarFilter[FFT_SIZE]; // Filter coefficients for the right ear

SOFA::getHRTFFilters(leftEarFilter, rightEarFilter);

// Apply the filters to the audio signal
for (int i = 0; i < audioSignalLength; i++) {
    float leftEarOutput = leftEarFilter[i] * audioSignal[i];
    float rightEarOutput = rightEarFilter[i] * audioSignal[i];

    // Apply the left and right ear outputs to the audio playback system
    // ...
}

2. Ambisonics

Ambisonics is a spatial audio technique that represents sound as a sum of spherical harmonics, capturing both the direction and magnitude of sound sources in a spherical soundfield. It provides a flexible approach to spatialization, allowing for precise positioning and immersive sound reproduction.

In order to implement Ambisonics-based spatialization, a set of Ambisonics encoding and decoding algorithms is required. Libraries such as the Ambisonic Toolkit (ATK) provide a comprehensive set of functions for Ambisonics processing, including encoding sound sources, decoding to different loudspeakers layouts, and binaural rendering for headphone playback.

Example code using the Ambisonic Toolkit for Ambisonics spatialization:

#include <ATK/encoding.h>
#include <ATK/decoding.h>
#include <ATK/binaural.h>

// Encode sound sources into Ambisonics format
ATK::AmbisonicEncoder encoder;
encoder.addSoundSource(x, y, z, audioSignal1);
encoder.addSoundSource(x, y, z, audioSignal2);

ATK::AmbisonicSignal ambisonicsSignal = encoder.encode();

// Decode Ambisonics signal to loudspeakers layout
ATK::AmbisonicDecoder decoder;
decoder.setLoudspeakerLayout(ATK::Stereo);  // Example with stereo speakers

ATK::StereoSignal stereoSignal = decoder.decode(ambisonicsSignal);

// Apply binaural rendering for headphone playback
ATK::BinauralRenderer binauralRenderer;
binauralRenderer.setHeadRotation(angleX, angleY, angleZ);

ATK::BinauralSignal binauralSignal = binauralRenderer.render(stereoSignal);

// Apply the binaural signal to the headphone output
// ...

These are just a couple of examples of audio spatialization techniques implemented in C++. By incorporating these techniques into your audio applications, you can create immersive and realistic sound experiences for your users.

#audiospatialization #C++