fix: narrow SHM cleanup in profile handler to client semaphore only; add DC-blocking HPF to pipeline input (60Hz hum fix)

src/dsp/pipeline.py

@@ -352,6 +352,15 @@ class AudioPipeline:
         # load_preset() holds it only for the atomic swap (not during model I/O).
         self._lock = threading.Lock()
 
+        # ── DC-blocking filter state ───────────────────────────────────────
+        # Single-pole high-pass at ~15Hz to remove DC offset and subsonic
+        # noise that can amplify into audible hum through NAM models.
+        # Filter: y[n] = alpha * (y[n-1] + x[n] - x[n-1])
+        # where alpha = 1 / (1 + 2*pi*fc/sr)
+        self._dc_prev_x: float = 0.0
+        self._dc_prev_y: float = 0.0
+        self._dc_alpha: float = 1.0 / (1.0 + 2.0 * np.pi * 15.0 / 48000.0)
+
         logger.info("Audio pipeline initialized (block=%d, sr=%d)",
                      self._block_size, self._sample_rate)
 
@@ -646,6 +655,21 @@ class AudioPipeline:
         )
 
         buf = audio_in.copy()
+        # ── DC-blocking high-pass filter ────────────────────────────
+        # Removes DC offset and subsonic noise (~15Hz corner) that can
+        # amplify into audible hum through high-gain NAM models.
+        # First-order HPF: y[n] = alpha * (y[n-1] + x[n] - x[n-1])
+        alpha = self._dc_alpha
+        px = self._dc_prev_x
+        py = self._dc_prev_y
+        for i in range(len(buf)):
+            y = alpha * (py + buf[i] - px)
+            px = buf[i]
+            py = y
+            buf[i] = y
+        self._dc_prev_x = px
+        self._dc_prev_y = py
+        
         for idx, entry in enumerate(chain):
             if entry["bypass"] or not entry["enabled"]:
                 continue
@@ -683,6 +707,23 @@ class AudioPipeline:
         ch0 = audio_in[0, :].copy()
         ch1 = audio_in[1, :].copy()
 
+        # ── DC-blocking high-pass filter on both channels ───────────
+        alpha = self._dc_alpha
+        px = self._dc_prev_x
+        py = self._dc_prev_y
+        for i in range(len(ch0)):
+            y = alpha * (py + ch0[i] - px)
+            px = ch0[i]
+            py = y
+            ch0[i] = y
+        for i in range(len(ch1)):
+            y = alpha * (py + ch1[i] - px)
+            px = ch1[i]
+            py = y
+            ch1[i] = y
+        self._dc_prev_x = px
+        self._dc_prev_y = py
+
         # Update input VU level from the guitar input channel (ch0)
         in_rms = np.sqrt(np.mean(ch0 ** 2) + _EPS)
         self._input_level = (
@@ -3102,6 +3143,7 @@ class AudioPipeline:
         self._block_size = block_size
         self._sample_rate = sample_rate
         self._vu_alpha = np.exp(-block_size / (0.05 * sample_rate))
+        self._dc_alpha = 1.0 / (1.0 + 2.0 * np.pi * 15.0 / sample_rate)
         # Clear DSP state — effects will reinit with new block/sample rate
         self._state.clear()
         self._coeffs.clear()

src/web/server.py

@@ -1768,14 +1768,15 @@ class WebServer:
             # Clean stale client SHM before creating new JACK client.
             # The old process's jack.Client __del__ can recreate the
             # pi-multifx semaphore after stop_jack() cleaned it.
+            # IMPORTANT: Only target our client's semaphore, NOT the
+            # running JACK server's files (jack_sem.*_system, jack-shm-registry,
+            # jack_db-0/) — deleting those between start_jack() and
+            # jack_client.start() kills the JACK server socket and makes
+            # the client connection fail silently.
             try:
                 from pathlib import Path
-                import shutil
-                for p in Path("/dev/shm").glob("jack*"):
-                    if p.is_dir():
-                        shutil.rmtree(p, ignore_errors=True)
-                    else:
-                        p.unlink(missing_ok=True)
+                for p in Path("/dev/shm").glob("jack_sem.*.default_pi-multifx*"):
+                    p.unlink(missing_ok=True)
             except Exception:
                 pass