void DspLimiter::Process(DspChunk& chunk)
{
if (chunk.IsEmpty())
return;
if (!m_exclusive || (chunk.GetFormat() != DspFormat::Float &&
chunk.GetFormat() != DspFormat::Double))
{
m_active = false;
return;
}
m_active = true;
// Analyze samples
float peak;
if (chunk.GetFormat() == DspFormat::Double)
{
double largePeak = GetPeak((double*)chunk.GetData(), chunk.GetSampleCount());
peak = std::nexttoward((float)largePeak, largePeak);
}
else
{
assert(chunk.GetFormat() == DspFormat::Float);
peak = GetPeak((float*)chunk.GetData(), chunk.GetSampleCount());
}
// Configure limiter
if (peak > 1.0f)
{
if (m_holdWindow <= 0)
{
NewTreshold(std::max(peak, 1.4f));
}
else if (peak > m_peak)
{
NewTreshold(peak);
}
m_holdWindow = (int64_t)m_rate * m_channels * 10; // 10 seconds
}
// Apply limiter
if (m_holdWindow > 0)
{
if (chunk.GetFormat() == DspFormat::Double)
{
ApplyLimiter<double>((double*)chunk.GetData(), chunk.GetSampleCount(), m_threshold);
}
else
{
assert(chunk.GetFormat() == DspFormat::Float);
ApplyLimiter((float*)chunk.GetData(), chunk.GetSampleCount(), m_threshold);
}
m_holdWindow -= chunk.GetSampleCount();
}
}
void DesignAudioBiquadIIR_q31_t(q31_t_IIR_Coefficients *C,// Pointer to the IIR Structure
uint8_t FilterType,
float Fs, //System Sample Rate
float f0, //("wherever it's happenin', man." Center Frequency or
//Corner Frequency, or shelf midpoint frequency, depending
//on which filter type. The "significant frequency".)*/
float Q,//(the EE kind of definition, except for peakingEQ in which A*Q is
// the classic EE Q. That adjustment in definition was made so that
// a boost of N dB followed by a cut of N dB for identical Q and
// f0/Fs results in a precisely flat unity gain filter or "wire".)*/
float dBgain// (used only for peaking and shelving filters)
)
{
A = sqrt(pow(10,(dBgain/40)));
if(Fs == 0) Fs = 1000;
if(Q == 0) Q = 1.0;
w0 = 2.0*3.141592654*f0/Fs;
alpha = sin(w0)/(2.0 * Q);
switch(FilterType)
{
default:
case BIQUAD_LOW_PASS_FILTER :
b0 = (1 - cos(w0))/2;
b1 = 1 - cos(w0);
b2 = (1 - cos(w0))/2;
a0 = 1 + alpha;
a1 = -2*cos(w0);
a2 = 1 - alpha;
break;
case BIQUAD_HIGH_PASS_FILTER :
b0 = (1 + cos(w0))/2;
b1 = -(1 + cos(w0));
b2 = (1 + cos(w0))/2;
a0 = 1 + alpha;
a1 = -2*cos(w0);
a2 = 1 - alpha;
break;
case BIQUAD_BAND_PASS_FILTER_CONSTANT_SKIRT_GAIN_PEAKGAIN_Q :
b0 = Q*alpha;
b1 = 0;
b2 = -Q*alpha;
a0 = 1 + alpha;
a1 = -2*cos(w0);
a2 = 1 - alpha;
break;
case BIQUAD_BAND_PASS_FILTER_CONSTANT_0_DB_PEAK_GAIN:
b0 = alpha;
b1 = 0;
b2 = -alpha;
a0 = 1 + alpha;
a1 = -2*cos(w0);
a2 = 1 - alpha;
break;
case BIQUAD_NOTCH_FILTER:
b0 = 1;
b1 = -2*cos(w0);
b2 = 1;
a0 = 1 + alpha;
a1 = -2*cos(w0);
a2 = 1 - alpha;
break;
case BIQUAD_ALL_PASS_FILTER:
b0 = 1 - alpha;
b1 = -2*cos(w0);
b2 = 1 + alpha;
a0 = 1 + alpha;
a1 = -2*cos(w0);
a2 = 1 - alpha;
break;
case BIQUAD_PEAKING_EQ:
b0 = 1 + alpha*A;
b1 = -2*cos(w0);
b2 = 1 - alpha*A;
a0 = 1 + alpha/A;
a1 = -2*cos(w0);
a2 = 1 - alpha/A;
break;
case BIQUAD_LOW_SHELF:
b0 = A*( (A+1.0) - (A-1.0)*cos(w0) + 2.0*sqrt(A)*alpha );
b1 = 2.0*A*( (A-1.0) - (A+1.0)*cos(w0) );
b2 = A*( (A+1.0) - (A-1.0)*cos(w0) - 2.0*sqrt(A)*alpha );
a0 = (A+1.0) + (A-1.0)*cos(w0) + 2.0*sqrt(A)*alpha;
a1 = -2.0*( (A-1.0) + (A+1.0)*cos(w0) );
a2 = (A+1.0) + (A-1.0)*cos(w0) - 2.0*sqrt(A)*alpha;
break;
case BIQUAD_HIGH_SHELF:
b0 = A*( (A+1) + (A-1)*cos(w0) + 2*sqrt(A)*alpha );
b1 = -2*A*( (A-1) + (A+1)*cos(w0) );
b2 = A*( (A+1) + (A-1)*cos(w0) - 2*sqrt(A)*alpha );
a0 = (A+1) - (A-1)*cos(w0) + 2*sqrt(A)*alpha;
a1 = 2*( (A-1) - (A+1)*cos(w0) );
a2 = (A+1) - (A-1)*cos(w0) - 2*sqrt(A)*alpha;
break;
}
/*
The most straight forward implementation would be the "Direct Form 1"
(Eq 2):
y[n] = (b0/a0)*x[n] + (b1/a0)*x[n-1] + (b2/a0)*x[n-2]
- (a1/a0)*y[n-1] - (a2/a0)*y[n-2] (Eq 4)
but to make things easier on the chip, we will do all adds:
y[n] = (b0/a0)*x[n] + (b1/a0)*x[n-1] + (b2/a0)*x[n-2]
+ (a1/a0)*y[n-1] + (a2/a0)*y[n-2] (Eq 4)
THis means that 2 feedback coef. have to be inverted
*/
b0 = b0/a0;
b1 = b1/a0;
b2 = b2/a0;
a1 = a1/a0;
a2 = a2/a0;
a0 = 1.0;
a1 = a1 * -1.0;
a2 = a2 * -1.0;
C->PostShift = 0;
while(GetPeak(&coef[0],6) > 1.0)
{
C->PostShift++;
b0 = b0/(float)(1<<C->PostShift);
b1 = b1/(float)(1<<C->PostShift);
b2 = b2/(float)(1<<C->PostShift);
a1 = a1/(float)(1<<C->PostShift);
a2 = a2/(float)(1<<C->PostShift);
a0 = a0/(float)(1<<C->PostShift);
}
C->a[0] = (q31_t)(0x7FFFFFFF * a1); //a[0] in the IIR struct is actually a1
C->a[1] = (q31_t)(0x7FFFFFFF * a2); //a[1] in the IIR struct is actually a2
C->b[0] = (q31_t)(0x7FFFFFFF * b0);
C->b[1] = (q31_t)(0x7FFFFFFF * b1);
C->b[2] = (q31_t)(0x7FFFFFFF * b2);
return;
}
