rhythm909: build at sample rates below 32 kHz

lib/audioinstruments/_rack/dsp/drums.py

@@ -1162,10 +1162,15 @@ def _build_hold(self):
         elif audioshaper is not None:
             self.bridge = NodeBridge(block_size, self.sample_rate)
             self.sample_hold = audioshaper.SampleHold(
-                self.bridge.source, self.sample_rate, int(round(self.rate))
+                self.bridge.source, self.sample_rate, self._hold_rate()
             )
             self.bridge.chain(self.sample_hold, direct=False)
 
+    def _hold_rate(self):
+        # The hold only drops frames, so it cannot run faster than the output:
+        # callers that ask for 32 kHz on a 24 kHz output get a hold of 24 kHz.
+        return min(int(round(self.rate)), self.sample_rate)
+
     def _hold_clear(self):
         # Armed so that the first frames refresh, the way the node's clear() leaves it.
         self._acc = self.sample_rate - 1
@@ -1177,7 +1182,7 @@ def _hold(self, src, dst):
         Every array is made once in _build_hold, so a block allocates nothing.
         """
         num = self.sample_rate
-        den = int(round(self.rate))
+        den = self._hold_rate()
         n = len(src)
         count = self._count[:n]
         np.multiply(self._ahead[:n], den, out=count)
@@ -1212,7 +1217,7 @@ def set_rate(self, rate_hz):
             self.rate = r
             self._update_anti_alias()
             if self.sample_hold is not None:
-                self.sample_hold.set(self.sample_rate, int(round(self.rate)))
+                self.sample_hold.set(self.sample_rate, self._hold_rate())
 
     def _update_anti_alias(self):
         cutoff = min(self.rate * 0.45, self.sample_rate * 0.45)

tests/mpy/test_rhythm909.py

@@ -164,3 +164,16 @@ def test_crusher_follows_its_input_and_settles_to_zero():
     for _ in range(6):
         crusher.process(src, dst)
     assert max(abs(dst[i]) for i in range(128)) == 0.0
+
+
+def test_builds_and_sounds_below_32_khz():
+    """The crusher's 32 kHz hold cannot exceed the output rate: 22.05 and 24 kHz must build."""
+    for rate in (22050, 24000):
+        inst = adapter.create(rate, voice="rhythm909", engine="rack")
+        for pad in VOICE_PADS:
+            inst.note_on(pad, 100)
+            top = peak(pulled(inst, 15))
+            assert top > 300, "Pad %d at %d Hz is too quiet: %d" % (pad, rate, top)
+            inst.all_notes_off()
+            pulled(inst, 20)
+        inst.deinit()