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ladder.cpp
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ladder.cpp
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/* Ported from Audio Library for Teensy, Ladder Filter
* Copyright (c) 2021, Richard van Hoesel
* Copyright (c) 2024, Infrasonic Audio LLC
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice, development funding notice, and this permission
* notice shall be included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
//-----------------------------------------------------------
// Huovilainen New Moog (HNM) model as per CMJ jun 2006
// Richard van Hoesel, v. 1.03, Feb. 14 2021
// v1.7 (Infrasonic/Daisy) add configurable filter mode
// v1.6 (Infrasonic/Daisy) removes polyphase FIR, uses 2x linear
// oversampling for performance reasons
// v1.5 adds polyphase FIR or Linear interpolation
// v1.4 FC extended to 18.7kHz, max res to 1.8, 4x oversampling,
// and a minor Q-tuning adjustment
// v.1.03 adds oversampling, extended resonance,
// and exposes parameters input_drive and passband_gain
// v.1.02 now includes both cutoff and resonance "CV" modulation inputs
// please retain this header if you use this code.
//-----------------------------------------------------------
#include "ladder.h"
#include "Utility/dsp.h"
using namespace daisysp;
static inline float fast_tanh(float x)
{
if(x > 3.0f)
return 1.0f;
if(x < -3.0f)
return -1.0f;
float x2 = x * x;
return x * (27.0f + x2) / (27.0f + 9.0f * x2);
}
void LadderFilter::Init(float sample_rate)
{
sample_rate_ = sample_rate;
sr_int_recip_ = 1.0f / (sample_rate * kInterpolation);
alpha_ = 1.0f;
K_ = 1.0f;
Fbase_ = 1000.0f;
Qadjust_ = 1.0f;
oldinput_ = 0.f;
mode_ = FilterMode::LP24;
SetPassbandGain(0.5f);
SetInputDrive(0.5f);
SetFreq(5000.f);
SetRes(0.2f);
}
float LadderFilter::Process(float in)
{
float input = in * drive_;
float total = 0.0f;
float interp = 0.0f;
for(size_t os = 0; os < kInterpolation; os++)
{
float u = (interp * oldinput_ + (1.0f - interp) * input)
- (z1_[3] - pbg_ * input) * K_ * Qadjust_;
u = fast_tanh(u);
float stage1 = LPF(u, 0);
float stage2 = LPF(stage1, 1);
float stage3 = LPF(stage2, 2);
float stage4 = LPF(stage3, 3);
total += weightedSumForCurrentMode(
{input, stage1, stage2, stage3, stage4})
* kInterpolationRecip;
interp += kInterpolationRecip;
}
oldinput_ = input;
return total;
}
__attribute__((optimize("unroll-loops"))) void
LadderFilter::ProcessBlock(float* buf, size_t size)
{
for(size_t i = 0; i < size; i++)
{
buf[i] = Process(buf[i]);
}
}
void LadderFilter::SetFreq(float freq)
{
Fbase_ = freq;
compute_coeffs(freq);
}
void LadderFilter::SetRes(float res)
{
// maps resonance = 0->1 to K = 0 -> 4
res = daisysp::fclamp(res, 0.0f, kMaxResonance);
K_ = 4.0f * res;
}
void LadderFilter::SetPassbandGain(float pbg)
{
pbg_ = daisysp::fclamp(pbg, 0.0f, 0.5f);
SetInputDrive(drive_);
}
void LadderFilter::SetInputDrive(float odrv)
{
drive_ = daisysp::fmax(odrv, 0.0f);
if(drive_ > 1.0f)
{
drive_ = fmin(drive_, 4.0f);
// max is 4 when pbg = 0, and 2.5 when pbg is 0.5
drive_scaled_ = 1.0f + (drive_ - 1.0f) * (1.0f - pbg_);
}
else
{
drive_scaled_ = drive_;
}
}
float LadderFilter::LPF(float s, int i)
{
// (1.0 / 1.3) (0.3 / 1.3)
float ft = s * 0.76923077f + 0.23076923f * z0_[i] - z1_[i];
ft = ft * alpha_ + z1_[i];
z1_[i] = ft;
z0_[i] = s;
return ft;
}
void LadderFilter::compute_coeffs(float freq)
{
freq = daisysp::fclamp(freq, 5.0f, sample_rate_ * 0.425f);
float wc = freq * 2.0f * PI_F * sr_int_recip_;
float wc2 = wc * wc;
alpha_ = 0.9892f * wc - 0.4324f * wc2 + 0.1381f * wc * wc2
- 0.0202f * wc2 * wc2;
//Qadjust = 1.0029f + 0.0526f * wc - 0.0926 * wc2 + 0.0218* wc * wc2;
Qadjust_ = 1.006f + 0.0536f * wc - 0.095f * wc2 - 0.05f * wc2 * wc2;
// revised hfQ (rvh - feb 14 2021)
}
float LadderFilter::weightedSumForCurrentMode(
const std::array<float, 5>& stage_outs)
{
// Weighted filter stage mixing to achieve selected response
// as described in "Oscillator and Filter Algorithms for Virtual Analog Synthesis"
// Välimäki and Huovilainen, Computer Music Journal, vol 60, 2006
switch(mode_)
{
case FilterMode::LP24: return stage_outs[4];
case FilterMode::LP12: return stage_outs[2];
case FilterMode::BP24:
return (stage_outs[2] + stage_outs[4]) * 4.0f
- stage_outs[3] * 8.0f;
case FilterMode::BP12: return (stage_outs[1] - stage_outs[2]) * 2.0f;
case FilterMode::HP24:
return stage_outs[0] + stage_outs[4]
- ((stage_outs[1] + stage_outs[3]) * 4.0f)
+ stage_outs[2] * 6.0f;
case FilterMode::HP12:
return stage_outs[0] + stage_outs[2] - stage_outs[1] * 2.0f;
default: return 0.0f;
}
}