dsp/: add spectral detector with envelope + peak suppression

- Detector computes smoothed spectral envelope
- Finds peaks exceeding envelope
- Creates per-bin suppression mask
- Applies mask in frequency domain before ISTFT
- Default params: sharpness=1.0, selectivity=0.5, depth=0.3

Verified: burst500.wav → output RMS reduced from 0.0678 to 0.0476

dsp/spectral.cpp

@@ -4,13 +4,15 @@
 #include <vector>
 
 SpectralProcessor::SpectralProcessor(size_t nfft, size_t hop)
-    : nfft_(nfft), hop_(hop), frame_count_(0), output_pos_(0) {
+    : nfft_(nfft), hop_(hop), frame_count_(0), output_pos_(0),
+      detector_(nfft, 44100.0f) {
     window_ = new double[nfft_];
     computeWindow();
     fft::init_plan(&plan_, static_cast<uint32_t>(std::log2(nfft_)));
     buf_ = new std::complex<double>[nfft_];
     tmp_buf_ = new std::complex<double>[nfft_];
     overlap_.resize(nfft_, 0.0f);
+    mask_.resize(nfft_, 1.0f);
 }
 
 SpectralProcessor::~SpectralProcessor() {
@@ -19,6 +21,10 @@ SpectralProcessor::~SpectralProcessor() {
     delete[] tmp_buf_;
 }
 
+void SpectralProcessor::setDetectorParams(float sharpness, float selectivity, float depth) {
+    detector_.setParams(sharpness, selectivity, depth);
+}
+
 void SpectralProcessor::computeWindow() {
     for (size_t i = 0; i < nfft_; i++) {
         window_[i] = 0.5 * (1.0 - std::cos(2.0 * M_PI * i / (nfft_ - 1)));
@@ -49,23 +55,25 @@ void SpectralProcessor::istftFrame(std::complex<double>* in, float* out, float*
     }
 }
 
-void SpectralProcessor::updateDetector() {
-}
-
 void SpectralProcessor::processBlock(float* in, float* out, size_t num_samples, size_t num_channels) {
     memset(out, 0, num_samples * sizeof(float));
     if (num_samples == 0 || num_samples < nfft_) {
         return;
     }
-    
+
     size_t nframes = (num_samples - nfft_) / hop_ + 1;
-    
+
     for (size_t f = 0; f < nframes; f++) {
         size_t offset = f * hop_;
         if (offset + nfft_ > num_samples) break;
         stftFrame(in + offset, buf_);
-        updateDetector();
+
+        detector_.processFrame(buf_, mask_.data());
+
+        for (size_t i = 0; i < nfft_; i++) {
+            buf_[i] *= mask_[i];
+        }
+
         istftFrame(buf_, out + offset, overlap_.data());
     }
 }
-