audiosampler: raise the voice ceiling from 64 to 128

ROADMAP.md

@@ -13,9 +13,6 @@ audio pump holding up under live use such as a stompbox or a stage rig.
 - A level ramp on `audiomixer` voices: a level move ramps over a set number of
   frames instead of stepping, so an effect can fade its wet path in or out
   without a click when you switch it in mid-note.
-- More sampler voices: `audiosampler.Sampler` caps at 64 voices
-  (`SAMPLER_MAX_VOICES`), while 64 voices render in under half a millisecond per
-  21 ms period on a desktop. A dense General MIDI piece wants more.
 
 Bugs, and things you need that don't work yet, go to
 [issues](https://github.com/PyDevices/audiodsp/issues).

docs/upstream-diff.md

@@ -70,9 +70,19 @@ run). On an ESP32-P4 at 400 MHz, 64 voices of a dense General MIDI file
 took about 5 ms of the block before the frames between a voice's events got
 a loop of their own (state in registers, two frames' interpolation worked
 out together for the in-order core, the same arithmetic in the same order,
-so the same bits): about 2.4 ms after. Memory is the voice table (about 100 bytes a voice), a float
-accumulator of one block, and the output block. The buffers are the caller's,
-held by reference while a voice sounds.
+so the same bits): about 2.4 ms after. Memory is the voice table (about 100 bytes a voice, two
+slots each), a float accumulator of one block, and the output block. The
+buffers are the caller's, held by reference while a voice sounds.
+
+A `Sampler` carries up to 128 voices (`audiosampler.MAX_VOICES`). Cost
+grows with the voices sounding, not the table: a thousand and twenty-four
+frames (one 21.3 ms period) take 0.28 ms with 64 voices sounding and 0.55 ms
+with 128 on CPython, and 0.67 ms and 1.27 ms on the MicroPython unix port
+(x86-64, one core, every voice looping, panned and pitched apart); 64 voices
+sounding in a table of 128 take the same as in a table of 64. A board
+renders voices at its own pace, so scale the P4's 64 voices (2.4 ms of a
+5.3 ms block) to what you ask of it, and give `voice_count` the number it
+can keep up with.
 
 ### How it is verified
 

src/circuitpython_spike/shared-bindings/audiosampler/Sampler.c

@@ -39,7 +39,7 @@
 //|         samples_signed: bool = True,
 //|         sample_rate: int = 48000,
 //|     ) -> None:
-//|         """Create a sampler. ``voice_count`` (1 to 64) and ``channel_count``
+//|         """Create a sampler. ``voice_count`` (1 to 128) and ``channel_count``
 //|         (1 or 2) size the allocation and cannot change afterwards.
 //|         ``buffer_size`` is the output block in bytes, 256 frames by
 //|         default. ``bits_per_sample`` and ``samples_signed`` are accepted so

src/circuitpython_spike/shared-bindings/audiosampler/__init__.c

@@ -40,7 +40,7 @@
 //| """The most frames a block may carry (1024)."""
 //|
 //| MAX_VOICES: int
-//| """The most voices one Sampler may carry (64)."""
+//| """The most voices one Sampler may carry (128)."""
 //|
 //| LOOP_NONE: int
 //| """Play to the end of the buffer and stop (SoundFont sampleModes 0)."""

src/shared/audiodsp_sampler.h

@@ -73,9 +73,13 @@
 #define AUDIODSP_SAMPLER_MAX_FRAMES 1024u
 
 //: The most voices one sampler may carry. The budget target is 24 at 48 kHz
-//: stereo; 64 leaves headroom without letting a Python mistake allocate
-//: unboundedly.
-#define AUDIODSP_SAMPLER_MAX_VOICES 64u
+//: stereo. 128 covers a dense General MIDI piece, which has more than 60 keys
+//: down at once and the release tails of the notes just let go besides. It
+//: costs nothing until a voice sounds: a binding sizes its table to the
+//: `voice_count` it is asked for, at most this, and an idle voice is skipped,
+//: so a board that cannot render this many asks for fewer. The ceiling stops
+//: a Python mistake allocating without bound.
+#define AUDIODSP_SAMPLER_MAX_VOICES 128u
 
 //: Pitch bounds, as a ratio. 1/64 is six octaves down; 64 is six up.
 #define AUDIODSP_SAMPLER_MIN_PITCH (1.0f / 64.0f)

tests/test_cpython_audiosampler.py

@@ -32,6 +32,10 @@
 | S17 | 24 looping stereo voices render inside the 5333 us block | measured |
 | S18 | `play()` over a sounding voice fades the old note out under the new one, as S7 | exact |
 | S19 | A voice already releasing keeps releasing when stopped, no slower than the 5 ms fade | exact |
+| S20 | A Sampler of 128 voices builds, sounds on every voice and sums them; one more than `MAX_VOICES` is refused | exact; raises |
+| S21 | The first 64 voices of a table of 128 render what a table of 64 does | exact |
+| S22 | A steal on the last voice of a table of 128 fades the old note out, as S18 | exact |
+| S23 | 128 looping stereo voices render inside the 5333 us block | measured |
 
 S3 is this module's form of the identity trait `docs/correctness-standard.md`
 asks of every own node: an exact answer through the interpolator rather than
@@ -465,6 +469,74 @@ def test_s17_twenty_four_voices_inside_the_block(self):
         self.assertLess(best, budget)
 
 
+    def test_s20_a_hundred_and_twenty_eight_voices_sound_and_sum(self):
+        self.assertGreaterEqual(audiosampler.MAX_VOICES, 128)
+        sampler = mono(128)
+        self.assertEqual(len(sampler.voice), 128)
+        for voice in sampler.voice:
+            voice.play(flat(100), loop_mode=audiosampler.LOOP_FOREVER)
+        self.assertTrue(all(voice.playing for voice in sampler.voice))
+        render(sampler, 1)  # a new note's level ramps in across its first block
+        self.assertEqual(render(sampler, 1), [128 * 100] * BLOCK)
+        sampler.deinit()
+        with self.assertRaises(ValueError):
+            mono(audiosampler.MAX_VOICES + 1)
+
+    def test_s21_a_bigger_table_renders_the_same_for_the_voices_in_use(self):
+        cycle = sine_cycle()
+        outs = []
+        for table in (64, 128):
+            sampler = audiosampler.Sampler(voice_count=table, channel_count=2,
+                                           sample_rate=RATE)
+            for index in range(64):
+                sampler.voice[index].play(
+                    cycle, pitch=2.0 ** ((index % 24 - 12) / 12.0),
+                    loop_mode=audiosampler.LOOP_FOREVER, level=0.01,
+                    pan=(index % 5 - 2) / 2.0, attack=0.01, decay=0.5,
+                    sustain=0.5)
+            outs.append(render(sampler, 8))
+            sampler.deinit()
+        self.assertGreater(peak(outs[0]), 1000)
+        self.assertEqual(outs[0], outs[1])
+
+    def test_s22_a_steal_on_the_last_voice_fades_the_old_note(self):
+        sampler = mono(128)
+        for voice in sampler.voice[:127]:
+            voice.play(flat(10), loop_mode=audiosampler.LOOP_FOREVER)
+        sampler.voice[127].play(flat(), loop_mode=audiosampler.LOOP_FOREVER)
+        render(sampler, 2)
+        sampler.voice[127].play(flat(10000),
+                                loop_mode=audiosampler.LOOP_FOREVER)
+        out = render(sampler, 1)
+        self.assertFadesOut([v - 127 * 10 - 10000 for v in out], 20000)
+        self.assertEqual(render(sampler, 1), [127 * 10 + 10000] * BLOCK)
+        sampler.deinit()
+
+    def test_s23_a_hundred_and_twenty_eight_voices_inside_the_block(self):
+        sampler = audiosampler.Sampler(voice_count=128, channel_count=2,
+                                       sample_rate=RATE)
+        cycle = sine_cycle()
+        for index, voice in enumerate(sampler.voice):
+            voice.play(cycle, pitch=2.0 ** ((index % 24 - 12) / 12.0),
+                       loop_mode=audiosampler.LOOP_FOREVER, level=0.01,
+                       pan=(index % 5 - 2) / 2.0, attack=0.01, decay=0.5,
+                       sustain=0.5)
+        state = sampler._state
+        for _ in range(20):
+            state.render()
+        best = float("inf")
+        for _ in range(3):
+            started = time.perf_counter()
+            for _ in range(500):
+                state.render()
+            best = min(best, (time.perf_counter() - started) / 500 * 1e6)
+        budget = BLOCK / RATE * 1e6
+        print("\n128 looping stereo voices: %.1f us per %d-frame block "
+              "(budget %.0f us)" % (best, BLOCK, budget))
+        self.assertTrue(all(voice.playing for voice in sampler.voice))
+        self.assertLess(best, budget)
+
+
 class SampleBufferTraits(unittest.TestCase):
     """Memory for samples: zeroed, writable through a view, and a voice
     playing from a view of it sounds as it does from an array."""