Vari-Mu Bus Compressor + EQ
Lake Ontario
A 2-channel Vari-Mu bus compressor with a full 4-band EQ per channel - glue and tone-shaping in the same signal path.
The DSP behind the faceplate.
A screenshot proves visual design. It does not prove the plugin actually processes audio correctly. Below is real, unedited C++ from Magic Buss’s six-band parametric EQ: production source, currently shipping, not a demo written for this portfolio.
RBJ Cookbook formsDirect-form-I biquad, standard peaking/shelf/highpass/lowpass derivations
Six-band routingConfigurable HP/LP slopes, per-band bypass, stereo dual-mono
Real-time safeNo allocation in the audio callback, coefficients recomputed only on parameter change
Biquad coefficient mathDSP/ParametricEQ.h
Peaking, shelf, highpass, and lowpass coefficient derivations, plus the direct-form-I process step.
struct Biquad
{
float b0 = 1.f, b1 = 0.f, b2 = 0.f, a1 = 0.f, a2 = 0.f;
float z1 = 0.f, z2 = 0.f;
void reset() { z1 = z2 = 0.f; }
inline float process(float x)
{
const float y = b0 * x + z1;
z1 = b1 * x + z2 - a1 * y;
z2 = b2 * x - a2 * y;
return y;
}
void setBypass() { b0 = 1.f; b1 = b2 = a1 = a2 = 0.f; }
void setPeaking(double sr, float freq, float q, float gainDb)
{
const double A = std::pow(10.0, gainDb / 40.0);
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double alpha = std::sin(w0) / (2.0 * juce::jmax(0.05, (double)q));
const double cosw0 = std::cos(w0);
const double a0 = 1.0 + alpha / A;
b0 = (float)((1.0 + alpha * A) / a0);
b1 = (float)((-2.0 * cosw0) / a0);
b2 = (float)((1.0 - alpha * A) / a0);
a1 = (float)((-2.0 * cosw0) / a0);
a2 = (float)((1.0 - alpha / A) / a0);
}
void setLowShelf(double sr, float freq, float q, float gainDb)
{
const double A = std::pow(10.0, gainDb / 40.0);
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double cosw0 = std::cos(w0);
const double sinw0 = std::sin(w0);
const double alpha = sinw0 / 2.0 * (1.0 / juce::jmax(0.05, (double)q));
const double twoSqrtAalpha = 2.0 * std::sqrt(A) * alpha;
const double a0 = (A + 1.0) + (A - 1.0) * cosw0 + twoSqrtAalpha;
b0 = (float)(A * ((A + 1.0) - (A - 1.0) * cosw0 + twoSqrtAalpha) / a0);
b1 = (float)(2.0 * A * ((A - 1.0) - (A + 1.0) * cosw0) / a0);
b2 = (float)(A * ((A + 1.0) - (A - 1.0) * cosw0 - twoSqrtAalpha) / a0);
a1 = (float)(-2.0 * ((A - 1.0) + (A + 1.0) * cosw0) / a0);
a2 = (float)(((A + 1.0) + (A - 1.0) * cosw0 - twoSqrtAalpha) / a0);
}
void setHighShelf(double sr, float freq, float q, float gainDb)
{
const double A = std::pow(10.0, gainDb / 40.0);
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double cosw0 = std::cos(w0);
const double sinw0 = std::sin(w0);
const double alpha = sinw0 / 2.0 * (1.0 / juce::jmax(0.05, (double)q));
const double twoSqrtAalpha = 2.0 * std::sqrt(A) * alpha;
const double a0 = (A + 1.0) - (A - 1.0) * cosw0 + twoSqrtAalpha;
b0 = (float)(A * ((A + 1.0) + (A - 1.0) * cosw0 + twoSqrtAalpha) / a0);
b1 = (float)(-2.0 * A * ((A - 1.0) + (A + 1.0) * cosw0) / a0);
b2 = (float)(A * ((A + 1.0) + (A - 1.0) * cosw0 - twoSqrtAalpha) / a0);
a1 = (float)(2.0 * ((A - 1.0) - (A + 1.0) * cosw0) / a0);
a2 = (float)(((A + 1.0) - (A - 1.0) * cosw0 - twoSqrtAalpha) / a0);
}
void setHighpass(double sr, float freq, float q)
{
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double cosw0 = std::cos(w0);
const double alpha = std::sin(w0) / (2.0 * juce::jmax(0.05, (double)q));
const double a0 = 1.0 + alpha;
b0 = (float)(((1.0 + cosw0) / 2.0) / a0);
b1 = (float)((-(1.0 + cosw0)) / a0);
b2 = (float)(((1.0 + cosw0) / 2.0) / a0);
a1 = (float)((-2.0 * cosw0) / a0);
a2 = (float)((1.0 - alpha) / a0);
}
void setLowpass(double sr, float freq, float q)
{
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double cosw0 = std::cos(w0);
const double alpha = std::sin(w0) / (2.0 * juce::jmax(0.05, (double)q));
const double a0 = 1.0 + alpha;
b0 = (float)(((1.0 - cosw0) / 2.0) / a0);
b1 = (float)((1.0 - cosw0) / a0);
b2 = (float)(((1.0 - cosw0) / 2.0) / a0);
a1 = (float)((-2.0 * cosw0) / a0);
a2 = (float)((1.0 - alpha) / a0);
}
// One-pole, used for the 6dB/oct slope option.
void setOnePoleHighpass(double sr, float freq)
{
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double k = std::tan(w0 / 2.0);
const double a0 = 1.0 + k;
b0 = (float)( 1.0 / a0);
b1 = (float)(-1.0 / a0);
b2 = 0.f;
a1 = (float)(-(1.0 - k) / a0);
a2 = 0.f;
}
void setOnePoleLowpass(double sr, float freq)
{
const double w0 = 2.0 * juce::MathConstants<double>::pi * freq / sr;
const double k = std::tan(w0 / 2.0);
const double a0 = 1.0 + k;
b0 = (float)(k / a0);
b1 = (float)(k / a0);
b2 = 0.f;
a1 = (float)(-(1.0 - k) / a0);
a2 = 0.f;
}
};Six-band routing and slope-stackingDSP/ParametricEQ.h
Configurable HP/LP slopes (6/12/18/24 dB per octave via cascaded one-pole and biquad sections), per-band enable, and the per-sample signal path.
class StereoChannelEQ
{
public:
void prepare(double sampleRate) { sr = sampleRate; reset(); }
void reset()
{
for (auto* f : { &hp1, &hp2, &lp1, &lp2, &low, &loMid, &hiMid, &high })
f->reset();
}
struct Settings
{
int hpSlope = 0; float hpFreq = 20.f;
int lpSlope = 0; float lpFreq = 20000.f;
bool lowShelf = true; float lowFreq = 100.f; float lowGain = 0.f; float lowQ = 0.7f; bool lowEnabled = true;
float loMidFreq = 300.f; float loMidGain = 0.f; float loMidQ = 0.7f; bool loMidEnabled = true;
float hiMidFreq = 3000.f; float hiMidGain = 0.f; float hiMidQ = 0.7f; bool hiMidEnabled = true;
bool highShelf = true; float highFreq = 8000.f; float highGain = 0.f; float highQ = 0.7f; bool highEnabled = true;
};
void update(const Settings& s)
{
hpSlope = s.hpSlope;
lpSlope = s.lpSlope;
if (s.hpSlope >= 1) hp1.setOnePoleHighpass(sr, s.hpFreq); else hp1.setBypass();
if (s.hpSlope >= 2) hp2.setHighpass(sr, s.hpFreq, 0.7071f); else hp2.setBypass();
// slopes 3 and 4 reuse hp2 as a second 2nd-order section for steeper roll-off
hp2b.setBypass();
if (s.hpSlope == 3) hp2b.setOnePoleHighpass(sr, s.hpFreq);
if (s.hpSlope == 4) hp2b.setHighpass(sr, s.hpFreq, 1.3066f);
if (s.lpSlope >= 1) lp1.setOnePoleLowpass(sr, s.lpFreq); else lp1.setBypass();
if (s.lpSlope >= 2) lp2.setLowpass(sr, s.lpFreq, 0.7071f); else lp2.setBypass();
lp2b.setBypass();
if (s.lpSlope == 3) lp2b.setOnePoleLowpass(sr, s.lpFreq);
if (s.lpSlope == 4) lp2b.setLowpass(sr, s.lpFreq, 1.3066f);
if (!s.lowEnabled) low.setBypass();
else if (s.lowShelf) low.setLowShelf(sr, s.lowFreq, s.lowQ, s.lowGain);
else low.setPeaking(sr, s.lowFreq, s.lowQ, s.lowGain);
if (!s.loMidEnabled) loMid.setBypass();
else loMid.setPeaking(sr, s.loMidFreq, s.loMidQ, s.loMidGain);
if (!s.hiMidEnabled) hiMid.setBypass();
else hiMid.setPeaking(sr, s.hiMidFreq, s.hiMidQ, s.hiMidGain);
if (!s.highEnabled) high.setBypass();
else if (s.highShelf) high.setHighShelf(sr, s.highFreq, s.highQ, s.highGain);
else high.setPeaking(sr, s.highFreq, s.highQ, s.highGain);
}
inline float process(float x)
{
if (hpSlope >= 1) x = hp1.process(x);
if (hpSlope >= 2) x = hp2.process(x);
if (hpSlope >= 3) x = hp2b.process(x);
x = low.process(x);
x = loMid.process(x);
x = hiMid.process(x);
x = high.process(x);
if (lpSlope >= 1) x = lp1.process(x);
if (lpSlope >= 2) x = lp2.process(x);
if (lpSlope >= 3) x = lp2b.process(x);
return x;
}
private:
double sr = 44100.0;
int hpSlope = 0, lpSlope = 0;
Biquad hp1, hp2, hp2b, lp1, lp2, lp2b;
Biquad low, loMid, hiMid, high;
};Magic Buss · channel-independent opto, VCA, and tube compressors with a six-band parametric EQ. This EQ stage runs identically regardless of which compressor character is selected.