private void Apply3DImpl(AudioListener listener, AudioEmitter emitter)
{
var vectDirWorldBase = emitter.Position - listener.Position;
var baseChangeMat = Matrix.Identity;
baseChangeMat.Row2 = new Vector4(listener.Up, 0);
baseChangeMat.Row3 = new Vector4(listener.Forward, 0);
baseChangeMat.Row1 = new Vector4(Vector3.Cross(listener.Up, listener.Forward), 0);
var vectDirListBase = Vector3.TransformNormal(vectDirWorldBase, baseChangeMat);
var azimut = 180f * (float)(Math.Atan2(vectDirListBase.X, vectDirListBase.Z)/Math.PI);
var elevation = 180f * (float)(Math.Atan2(vectDirListBase.Y, new Vector2(vectDirListBase.X, vectDirListBase.Z).Length())/Math.PI);
var distance = vectDirListBase.Length();
ComputeDopplerFactor(listener,emitter);
AudioVoice.Apply3D(azimut, elevation, distance / emitter.DistanceScale, MathUtil.Clamp((float)Math.Pow(2, Pitch) * dopplerPitchFactor, 0.5f, 2f));
}
private void Apply3DImpl(AudioListener listener, AudioEmitter emitter)
{
// Since android has no function available to perform sound 3D localization by default, here we try to mimic the behaviour of XAudio2
// After an analysis of the XAudio2 left/right stereo balance with respect to 3D world position,
// it could be found the volume repartition is symmetric to the Up/Down and Front/Back planes.
// Moreover the left/right repartition seems to follow a third degree polynomial function:
// Volume_left(a) = 2(c-1)*a^3 - 3(c-1)*a^2 + c*a , where c is a constant close to c = 1.45f and a is the angle normalized bwt [0,1]
// Volume_right(a) = 1-Volume_left(a)
// As for signal attenuation wrt distance the model follows a simple inverse square law function as explained in XAudio2 documentation
// ( http://msdn.microsoft.com/en-us/library/windows/desktop/microsoft.directx_sdk.x3daudio.x3daudio_emitter(v=vs.85).aspx )
// Volume(d) = 1 , if d <= ScaleDistance where d is the distance to the listener
// Volume(d) = ScaleDistance / d , if d >= ScaleDistance where d is the distance to the listener
// 1. Attenuation due to distance.
var vecListEmit = emitter.Position - listener.Position;
var distListEmit = vecListEmit.Length();
var attenuationFactor = distListEmit <= emitter.DistanceScale ? 1f : emitter.DistanceScale / distListEmit;
// 2. Left/Right balance.
var repartRight = 0.5f;
var worldToList = Matrix.Identity;
var rightVec = Vector3.Cross(listener.Forward, listener.Up);
worldToList.Column1 = new Vector4(rightVec, 0);
worldToList.Column2 = new Vector4(listener.Forward, 0);
worldToList.Column3 = new Vector4(listener.Up, 0);
var vecListEmitListBase = Vector3.TransformNormal(vecListEmit, worldToList);
var vecListEmitListBase2 = (Vector2)vecListEmitListBase;
if (vecListEmitListBase2.Length() > 0)
{
const float c = 1.45f;
var absAlpha = Math.Abs(Math.Atan2(vecListEmitListBase2.Y, vecListEmitListBase2.X));
var normAlpha = (float)(absAlpha / (Math.PI / 2));
if (absAlpha > Math.PI / 2) normAlpha = 2 - normAlpha;
repartRight = 0.5f * (2 * (c - 1) * normAlpha * normAlpha * normAlpha - 3 * (c - 1) * normAlpha * normAlpha * normAlpha + c * normAlpha);
if (absAlpha > Math.PI / 2) repartRight = 1 - repartRight;
}
// Set the volumes.
localizationChannelVolumes = new[] { attenuationFactor * (1f - repartRight), attenuationFactor * repartRight };
UpdateStereoVolumes();
// 3. Calculation of the Doppler effect
ComputeDopplerFactor(listener, emitter);
UpdatePitch();
}
public void Apply3D(AudioListener listener, AudioEmitter emitter)
{
DefaultInstance.Apply3D(listener, emitter);
}
private void ComputeDopplerFactor(AudioListener listener, AudioEmitter emitter)
{
// To evaluate the Doppler effect we calculate the distance to the listener from one wave to the next one and divide it by the sound speed
// we use 343m/s for the sound speed which correspond to the sound speed in the air.
// we use 600Hz for the sound frequency which correspond to the middle of the human hearable sounds frequencies.
const float SoundSpeed = 343f;
const float SoundFreq = 600f;
const float SoundPeriod = 1 / SoundFreq;
// avoid useless calculations.
if (emitter.DopplerScale <= float.Epsilon || (emitter.Velocity == Vector3.Zero && listener.Velocity == Vector3.Zero))
{
dopplerPitchFactor = 1f;
return;
}
var vecListEmit = emitter.Position - listener.Position;
var distListEmit = vecListEmit.Length();
var vecListEmitSpeed = emitter.Velocity - listener.Velocity;
if (Vector3.Dot(vecListEmitSpeed, Vector3.Normalize(vecListEmit)) < -SoundSpeed) // emitter and listener are getting closer more quickly than the speed of the sound.
{
dopplerPitchFactor = float.PositiveInfinity; // will be clamped later
return;
}
var timeSinceLastWaveArrived = 0f; // time elapsed since the previous wave arrived to the listener.
var lastWaveDistToListener = 0f; // the distance that the last wave still have to travel to arrive to the listener.
const float DistLastWave = SoundPeriod * SoundSpeed; // distance traveled by the previous wave.
if (DistLastWave > distListEmit)
timeSinceLastWaveArrived = (DistLastWave - distListEmit) / SoundSpeed;
else
lastWaveDistToListener = distListEmit - DistLastWave;
var nextVecListEmit = vecListEmit + SoundPeriod * vecListEmitSpeed;
var nextWaveDistToListener = nextVecListEmit.Length();
var timeBetweenTwoWaves = timeSinceLastWaveArrived + (nextWaveDistToListener - lastWaveDistToListener) / SoundSpeed;
var apparentFrequency = 1 / timeBetweenTwoWaves;
dopplerPitchFactor = (float) Math.Pow(apparentFrequency / SoundFreq, emitter.DopplerScale);
}
public void Apply3D(AudioListener listener, AudioEmitter emitter)
{
CheckNotDisposed();
if (listener == null)
throw new ArgumentNullException("listener");
if(emitter == null)
throw new ArgumentNullException("emitter");
if(soundEffect.WaveFormat.Channels > 1)
throw new InvalidOperationException("Apply3D cannot be used on multi-channels sounds.");
// reset Pan its default values.
if (Pan != 0)
Pan = 0;
if (EngineState != AudioEngineState.Invalidated)
Apply3DImpl(listener, emitter);
}
public void Apply3D(AudioListener listener, AudioEmitter emitter)
{
DefaultInstance.Apply3D(listener, emitter);
}