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// Tests the wav->spec->wav roundtrip SNR.
// Generates a sine wave, runs OLA-DCT analysis then IMDCT-OLA synthesis,
// and asserts the reconstruction SNR exceeds the threshold.
#include "audio/dct.h"
#include "audio/window.h"
#include <assert.h>
#include <cmath>
#include <cstdio>
#include <vector>
static const int SAMPLE_RATE = 32000;
static const float PI = 3.14159265358979323846f;
// Replicate analyze_audio OLA pass (Hann + FDCT, hop = OLA_HOP_SIZE)
static std::vector<float> ola_analyze(const std::vector<float>& pcm) {
float win[DCT_SIZE];
hann_window_512(win);
const int hop = OLA_HOP_SIZE;
const int n_pcm = (int)pcm.size();
const int num_frames = (n_pcm > DCT_SIZE) ? (n_pcm - DCT_SIZE) / hop + 1 : 1;
std::vector<float> spec(num_frames * DCT_SIZE);
float chunk[DCT_SIZE];
for (int f = 0; f < num_frames; ++f) {
const int start = f * hop;
const int avail = (start + DCT_SIZE <= n_pcm) ? DCT_SIZE : n_pcm - start;
for (int i = 0; i < avail; ++i) chunk[i] = pcm[start + i] * win[i];
for (int i = avail; i < DCT_SIZE; ++i) chunk[i] = 0.0f;
fdct_512(chunk, spec.data() + f * DCT_SIZE);
}
return spec;
}
// IDCT + OLA synthesis (no synthesis window) matching decode_to_wav.
// Analysis used Hann; since Hann satisfies w[n]+w[n+H]=1 at 50% overlap,
// skipping the synthesis window gives perfect reconstruction.
static std::vector<float> ola_decode(const std::vector<float>& spec,
int num_frames) {
std::vector<float> pcm(num_frames * OLA_HOP_SIZE + OLA_OVERLAP, 0.0f);
float overlap[OLA_OVERLAP] = {};
float tmp[DCT_SIZE];
for (int f = 0; f < num_frames; ++f) {
idct_512(spec.data() + f * DCT_SIZE, tmp);
for (int j = 0; j < OLA_HOP_SIZE; ++j)
pcm[f * OLA_HOP_SIZE + j] = tmp[j] + overlap[j];
for (int j = 0; j < OLA_OVERLAP; ++j)
overlap[j] = tmp[OLA_HOP_SIZE + j];
}
pcm.resize(num_frames * OLA_HOP_SIZE);
return pcm;
}
static float compute_snr_db(const std::vector<float>& ref,
const std::vector<float>& out,
int skip_samples) {
const int n = (int)std::min(ref.size(), out.size());
double sig = 0.0, noise = 0.0;
for (int i = skip_samples; i < n; ++i) {
sig += (double)ref[i] * ref[i];
double e = ref[i] - out[i];
noise += e * e;
}
if (noise < 1e-30) return 999.0f;
return 10.0f * (float)log10(sig / noise);
}
int main() {
printf("Running WAV roundtrip test...\n");
// 1-second 440 Hz sine at 32 kHz
const int n_samples = SAMPLE_RATE;
std::vector<float> input(n_samples);
for (int i = 0; i < n_samples; ++i)
input[i] = 0.5f * sinf(2.0f * PI * 440.0f * i / SAMPLE_RATE);
// Analyze
std::vector<float> spec = ola_analyze(input);
const int num_frames = (int)(spec.size() / DCT_SIZE);
// Decode with IDCT-OLA (no synthesis window)
std::vector<float> output = ola_decode(spec, num_frames);
// SNR — skip first DCT_SIZE samples (ramp-up transient)
const float snr = compute_snr_db(input, output, DCT_SIZE);
printf("Roundtrip SNR: %.1f dB (frames=%d, out_samples=%zu)\n",
snr, num_frames, output.size());
const float MIN_SNR_DB = 30.0f;
if (snr < MIN_SNR_DB) {
printf("FAIL: SNR %.1f dB < %.0f dB threshold\n", snr, MIN_SNR_DB);
return 1;
}
printf("PASS\n");
return 0;
}
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