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uus fft

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This commit is contained in:
Petri Järvisalo
2025-07-31 16:27:44 +03:00
parent 35c09187a4
commit aa949ba2a7
3 changed files with 52 additions and 88 deletions
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88
src/fft.cpp
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@ -1,78 +1,28 @@
#include "fft.h"
#include <math.h>
static float window[FFT_SIZE];
constexpr float PI = 3.14159;
constexpr float M_PI = 3.14159;
// In-place FFT on array of Complex numbers
void fft(Complex* x, int N, Complex* buffer) {
if (N <= 1) return;
Complex* even = buffer;
Complex* odd = buffer + N / 2;
// Call once before use
void init_hamming_window() {
for (int i = 0; i < FFT_SIZE; i++) {
window[i] = 0.54f - 0.46f * cosf(2.0f * (float)M_PI * i / (FFT_SIZE - 1));
}
}
static unsigned int bit_reverse(unsigned int x, int log2n) {
unsigned int n = 0;
for (int i = 0; i < log2n; i++) {
n <<= 1;
n |= (x & 1);
x >>= 1;
}
return n;
}
void compute_fft(float* time_data, float* freq_out) {
static float real[FFT_SIZE];
static float imag[FFT_SIZE];
int log2n = 0;
for (int t = FFT_SIZE; t > 1; t >>= 1) ++log2n;
// Apply Hamming window
for (int i = 0; i < FFT_SIZE; i++) {
real[i] = time_data[i] * window[i];
imag[i] = 0.0f;
for (int i = 0; i < N / 2; ++i) {
even[i] = x[i * 2];
odd[i] = x[i * 2 + 1];
}
// Bit reversal
for (int i = 0; i < FFT_SIZE; ++i) {
int j = bit_reverse(i, log2n);
if (j > i) {
float tmp_re = real[i], tmp_im = imag[i];
real[i] = real[j]; imag[i] = imag[j];
real[j] = tmp_re; imag[j] = tmp_im;
}
fft(even, N / 2, buffer + N); // deeper even
fft(odd, N / 2, buffer + N + N / 2); // deeper odd
for (int k = 0; k < N / 2; ++k) {
double angle = -2 * PI * k / N;
Complex twiddle(cos(angle), sin(angle));
Complex t = twiddle * odd[k];
x[k] = even[k] + t;
x[k + N / 2] = even[k] - t;
}
// Cooley-Tukey FFT
for (int s = 1; s <= log2n; ++s) {
int m = 1 << s;
for (int k = 0; k < FFT_SIZE; k += m) {
for (int j = 0; j < m / 2; ++j) {
int t = k + j;
int u = t + m / 2;
float angle = -2.0f * (float)M_PI * j / m;
float w_real = cosf(angle);
float w_imag = sinf(angle);
float re = w_real * real[u] - w_imag * imag[u];
float im = w_real * imag[u] + w_imag * real[u];
real[u] = real[t] - re;
imag[u] = imag[t] - im;
real[t] += re;
imag[t] += im;
}
}
}
for (int i = 0; i < FFT_SIZE / 2; ++i) {
float mag = sqrtf(real[i] * real[i] + imag[i] * imag[i]) / FFT_SIZE;
float db = 20.0f * log10f(mag + 1e-6f); // Decibels
float normalized = (db + 60.0f) / 60.0f; // [0,1]
freq_out[i] = mag;
}
}
}

15
src/fft.h
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@ -3,5 +3,16 @@
#include <math.h>
#define FFT_SIZE 2048
void init_hamming_window();
void compute_fft(float* time_data, float* freq_out);
// Simple complex number struct
struct Complex {
float re, im;
Complex(float r = 0, float i = 0) : re(r), im(i) {}
Complex operator+(const Complex& o) const { return { re + o.re, im + o.im }; }
Complex operator-(const Complex& o) const { return { re - o.re, im - o.im }; }
Complex operator*(const Complex& o) const {
return { re * o.re - im * o.im, re * o.im + im * o.re };
}
};
void fft(Complex* x, int N, Complex* buffer);

37
src/main.cpp
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@ -36,14 +36,25 @@
#include "fft.h"
#pragma data_seg(".pids")
// static allocation saves a few bytes
static int pidMain;
static int pidPost;
// static HDC hDC;
#ifndef EDITOR_CONTROLS
#pragma code_seg(".main")
// FFT buffers
static Complex signal[FFT_SIZE];
static Complex buffer[3 * FFT_SIZE];
static float fft_uniform[FFT_SIZE / 4];
static float shapesData[SHAPES_TEX_SIZE];
void entrypoint(void)
#else
#include "editor.h"
@ -112,7 +123,7 @@ int __cdecl main(int argc, char* argv[])
track.play();
double position = 0.0;
#endif
static float syncs[1 + SU_NUMSYNCS];
long playCursor = 0;
long lastPlayCursor = -1;
volatile float maximum = 0.0; // Helper variable to calculate maximum fft output for normalization
@ -123,17 +134,6 @@ int __cdecl main(int argc, char* argv[])
// Play sound
direct_sound_buffer->Play(0, 0, 0);
static float syncs[1 + SU_NUMSYNCS];
// Init FFT
init_hamming_window();
// FFT buffers
static float fft_input[FFT_SIZE];
static float fft_output[FFT_SIZE / 2]; // Magnitudes
static float fft_uniform[FFT_SIZE / 4];
static float shapesData[SHAPES_TEX_SIZE];
// main note effect
boolean beenPlaying = false;
const int SHAPES_SIZE = 15;
@ -221,7 +221,7 @@ int __cdecl main(int argc, char* argv[])
{
SUsample* samples = (SUsample*)audio_ptr;
for (int i = 0; i < FFT_SIZE; ++i) {
fft_input[i] = (float)samples[i];
signal[i] = Complex((float)samples[i], 0.0);
}
}
@ -229,20 +229,23 @@ int __cdecl main(int argc, char* argv[])
}
// Calculate FFT
compute_fft(fft_input, fft_output);
fft(signal, FFT_SIZE, buffer);
// Normalize output
for (int i = 0; i < (FFT_SIZE / 4); i++)
{
float gain = 50.0f;
float alpha = 0.10f; // "Hidastaa" FFT:n piikkej<EFBFBD>
float gain = 0.025f;
float alpha = 0.15f; // "Hidastaa" FFT:n piikkejä
float threshhold = 0.015f; // Alin arvo mik<69> p<><70>stet<65><74>n shaderille (v<>hent<6E><74> "noisea")
float x_t = (fft_output[i] < threshhold) ? 0.f : fft_output[i] * gain;
float magnitude = sqrt(signal[i].re * signal[i].re + signal[i].im * signal[i].im);
float x_t = (magnitude < threshhold) ? 0.f : magnitude * gain;
// Exponential smoothing kaava
// s(t) = alpha*x(t)+(1-alpha)*s(t-1)
fft_uniform[i] = alpha * (x_t)+(1 - alpha) * fft_uniform[i];
}
}
syncs[0] = (float)playCursor / (SU_SAMPLE_RATE * SU_CHANNEL_COUNT * SU_SAMPLE_SIZE); // Aika sekunteina.
for (int i = 0; i < SU_NUMSYNCS; ++i)