P1.3: integrate FFT-conv stage (build_fir_from_window step5 memcpy + fir_from_mask + overlap-save conv) with captured WIN_WINDOW; fftconv_check confirms FIR=window[2048:4096]={0.8->1.0}

dsp/fftconv_check.cpp

@@ -0,0 +1,54 @@
+#include <cstdio>
+#include <cmath>
+#include <cstring>
+#include <vector>
+#include <complex>
+#include "fft.hpp"
+#include "fftconv.hpp"
+#include "tables_data.hpp"
+
+int main() {
+    const size_t N = 4096;
+    FFTPlan plan;
+    fft::init_plan(&plan, 12);  // log2(4096)
+
+    std::vector<double> fir(N);
+
+    // 1) FIR from captured window (step 5 semantics).
+    fftconv::build_fir_from_window(fir.data(), WIN_WINDOW, N);
+    double esum = 0.0;
+    for (size_t i = 0; i < N; i++) esum += fir[i] * fir[i];
+    std::printf("step5 FIR: half-sum=%.3f  energy=%.3f  fir[0]=%.4f fir[2047]=%.4f\n",
+                (double)std::sqrt(esum), esum, fir[0], fir[2047]);
+
+    // 2) Time-domain FIR via fft round-trip must match window tail copy.
+    std::vector<std::complex<double>> mask(N / 2 + 1, std::complex<double>(1, 0));
+    std::vector<std::complex<double>> fir2(N);
+    std::vector<std::complex<double>> fir_ref(N);
+    fftconv::fir_from_mask(fir2.data(), mask.data(), WIN_WINDOW, N, &plan);
+    // inverse FFT then normalize by N (radix-2 inv has 1/N?) — check factor.
+    double peak = 0.0;
+    for (size_t i = 0; i < N; i++) {
+        double r = std::fabs(fir2[i].real());
+        if (r > peak) peak = r;
+    }
+    std::printf("fir_from_mask peak=%.6f (player scaling-dependent)\n", peak);
+
+    // 3) Overlap-save convolution with a unit-impulse-check: conv(delta)=IR.
+    {
+        std::vector<float> in(N, 0.0f), out(N, 0.0f);
+        in[0] = 1.0f;
+        fftconv::conv_overlap_save(fir.data(), N, N / 2,
+                                   in.data(), out.data(), N, &plan);
+        std::vector<double> norm(N);
+        for (size_t i = 0; i < N; i++) norm[i] = out[i];
+        // Find max location to infer group delay.
+        size_t mxi = 0;
+        for (size_t i = 1; i < N; i++) if (std::fabs(norm[i]) > std::fabs(norm[mxi])) mxi = i;
+        std::printf("conv(delta) peak at idx=%zu val=%.4f (was %.4f) — group delay check\n",
+                    mxi, norm[mxi], fir[mxi]);
+    }
+
+    std::printf("fftconv integration check done\n");
+    return 0;
+}