121 lines
2.3 KiB
C++
121 lines
2.3 KiB
C++
// Copyright Epic Games, Inc. All Rights Reserved.
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#include "DSP/SinOsc.h"
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namespace Audio
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{
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FSineOsc::FSineOsc()
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: SampleRate(0)
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, FrequencyHz(440.0f)
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, B1(0.0f)
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, B2(0.0f)
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, Yn_1(0.0f)
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, Yn_2(0.0f)
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, Scale(1.0f)
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, Add(0.0f)
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{
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}
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FSineOsc::FSineOsc(const int32 InSampleRate, const float InFrequencyHz, const float InScale, const float InAdd)
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: SampleRate(0)
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, FrequencyHz(440.0f)
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, B1(0.0f)
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, B2(0.0f)
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, Yn_1(0.0f)
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, Yn_2(0.0f)
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, Scale(InScale)
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, Add(InAdd)
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{
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Init(InSampleRate, InFrequencyHz);
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}
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FSineOsc::~FSineOsc()
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{
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}
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void FSineOsc::Init(const int32 InSampleRate, const float InFrequencyHz, const float InScale, const float InAdd)
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{
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check(InSampleRate > 0);
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check(InFrequencyHz > 0.0f);
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Scale = InScale;
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Add = InAdd;
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SampleRate = InSampleRate;
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FrequencyHz = -1.0f;
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SetFrequency(InFrequencyHz);
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}
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void FSineOsc::SetScale(const float InScale)
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{
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Scale = InScale;
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}
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void FSineOsc::SetAdd(const float InAdd)
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{
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Add = InAdd;
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}
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void FSineOsc::SetFrequency(const float InFrequencyHz)
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{
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check(SampleRate > 0);
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if (FrequencyHz == InFrequencyHz)
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{
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return;
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}
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FrequencyHz = InFrequencyHz;
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// Find new wT value
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const float OmegaT = 2.0f * PI * FrequencyHz / SampleRate;
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// set the biquad feedback coefficients using filter design equations
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B1 = -2.0f * FMath::Cos(OmegaT);
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B2 = 1.0f;
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// Set up initial conditions based on current state of the oscillator to avoid pops when dynamically changing frequencies
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Yn_1 = FMath::Clamp(Yn_1, -1.0f, 1.0f);
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// Get previous outputs phase
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const float OmegaTPrev = FMath::Asin(Yn_1);
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// Get N by dividing prev phase over new current phase
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float N = OmegaTPrev / FMath::Max(OmegaT, SMALL_NUMBER);
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// If currently on rising edge (newer value is higher)
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if (Yn_1 > Yn_2)
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{
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// new y(n-2) value will be Sin((N - 1) * wT)
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N -= 1.0f;
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}
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// If on falling edge (new value is lower)
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else
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{
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// new y(n-2) value will be Sin((N + 1) * wT)
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N += 1.0f;
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}
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Yn_2 = FMath::Sin(N * OmegaT);
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}
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float FSineOsc::GetFrequency() const
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{
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return FrequencyHz;
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}
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float FSineOsc::ProcessAudio()
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{
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// using direct-form difference equation
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// y(n) = -b1 * y(n - 1) - b2 * y(n - 2)
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const float Yn = -B1 * Yn_1 - B2 * Yn_2;
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// Move outputs down
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Yn_2 = Yn_1;
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Yn_1 = Yn;
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return Scale * Yn + Add;
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}
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}
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