Resync the CircuitPython modules with 11.0.0-alpha.2

AGENTS.md

@@ -90,7 +90,7 @@ of this repository in the parent workspace, same pattern as
   `.venv/bin/python tests/parity/verify_dsp.py --micropython ../micropython/ports/unix/build-pydevices/micropython`
   is the first. There is **no stored digest** — the gate is the comparison, and
   it **refuses a run with fewer than two interpreters** rather than passing one
-  that cannot fail. Add `--circuitpython ../bin/circuitpython-oracle-11.0.0-alpha.1`
+  that cannot fail. Add `--circuitpython ../bin/circuitpython-oracle-11.0.0-alpha.2`
   for the three-way. The arithmetic is all in `src/shared/`, so two
   interpreters disagreeing is never a difference of intent: it is a width, an
   undefined shift, a compiler's choice or an architecture.

CIRCUITPYTHON_ORACLE

@@ -1,9 +1,10 @@
 # The CircuitPython oracle pin. Every parity golden is measured against
-# this exact commit (tag 11.0.0-alpha.1; the pin moved from 10.3.0 on
-# 2026-10-08 with audiodsp#201, from 10.2.1 to 10.3.0 on 2026-09-09).
+# this exact commit (tag 11.0.0-alpha.2; the pin moved from 11.0.0-alpha.1 on
+# 2026-10-22, from 10.3.0 on 2026-10-08 with audiodsp#201, from 10.2.1 to
+# 10.3.0 on 2026-09-09).
 # Moving it is a re-port, not a bump: every move is a resync with upstream
-# (docs/upstream-sync.md; the last was audiodsp#220). See also AGENTS.md
-# "The CircuitPython oracle" and docs/upstream-diff.md. The 64-voice oracle binary built from
-# it lives at bin/circuitpython-oracle-11.0.0-alpha.1 (build_interpreters.sh
+# (docs/upstream-sync.md; the one before this was audiodsp#220). See also
+# AGENTS.md "The CircuitPython oracle" and docs/upstream-diff.md. The 64-voice oracle binary built from
+# it lives at bin/circuitpython-oracle-11.0.0-alpha.2 (build_interpreters.sh
 # cp-oracle); tests/test_voice_ceiling_consistency.py pins its sha256.
-11.0.0-alpha.1 520805e12127bdb51722ba1caa5c670ecd8c4f72
+11.0.0-alpha.2 d53b2277cfad71589028e5da77c984c045db990d

README.md

@@ -850,7 +850,7 @@ it.
 
 **CPython:** the public surface and wheel plumbing are present, and the
 committed synthesis, mixer, MIDI, streaming, and effects fixtures match
-CircuitPython 11.0.0-alpha.1 PCM byte-for-byte — built at the same voice ceiling this
+CircuitPython 11.0.0-alpha.2 PCM byte-for-byte — built at the same voice ceiling this
 port ships, which is the only comparison worth making. Import/API smoke success
 is not used as a substitute for those comparisons.
 

docs/upstream-diff.md

@@ -218,13 +218,64 @@ skipped on that probe, since its own nodes keep upstream's behaviour, and
 `pitchshift_freeze_probe.py` no longer renders after its reset, so it stays
 held to CircuitPython's bytes.
 
+## Resynced with 11.0.0-alpha.2
+
+The oracle moved from 11.0.0-alpha.1 to 11.0.0-alpha.2 (d53b2277c) on
+2026-10-22, with the binary at `bin/circuitpython-oracle-11.0.0-alpha.2`.
+Three upstream commits touched the ported code in between, all in
+`audiomixer` and `synthio_sat16`. What was taken is in
+[upstream-sync.md](upstream-sync.md#the-last-resync-1100-alpha2).
+
+**The mixer scales in integers (11a329885, fc57c0f36; adafruit/circuitpython#11617).**
+Upstream's non-DSP `mult16signed` was the float quotient `mul / 32767.0f`
+times the sample, truncated toward zero. It is `(ai * mul) >> 15` now, which
+upstream says "matches the DSP result bit for bit", and a centred pan is
+`32768 - panning` where it was `32767 - panning`. Both changes are in
+`src/audiomixer/Mixer.c`, in the CPython extension's scaling kernel
+(`src/cpython/_audiodsp.c`) and in its Python twin (`src/cpython/audiomixer.py`),
+as upstream has them. Three things follow:
+
+- Every level below 1.0 moves by up to one LSB. The divisor is 32768 where it
+  was 32767, and the shift floors where the cast truncated, so a small
+  negative sample rounds down: -1 at level 0.5 stays -1, where it used to
+  become 0. Material that never goes through a mixer voice below unity does
+  not move.
+- Level 1.0 is a wire without help. This port's unity branch is deleted, and
+  with it the difference recorded under
+  [A voice at level 1.0 is a wire](#a-voice-at-level-10-is-a-wire-audiodsp95).
+  On the CPython target the block-level shortcut that skips the scaling at
+  unity stays, keyed on Q15 32768 alone: 32767 used to scale by exactly 1.0
+  and no longer does.
+- A stereo voice at pan 0 is the same on both channels. The left channel no
+  longer sits one Q15 step below the right.
+
+`mixer_q15_level_probe.py` (it replaces `mixer_level_precision_probe.py`,
+whose material was the float32-versus-float64 flips that no longer exist)
+renders the rails and the values either side of zero at four levels and five
+pans, mono and stereo, and `verify_dsp.py` holds all three interpreters to
+the same bytes. A build from before the change prints different bytes from
+the oracle's.
+
+**`synthio_sat16` is inline (cbbde1208; adafruit/circuitpython#11621).** Taken
+as upstream has it in `src/synthio/__init__.h`. The rounding is the same
+arithmetic written without a branch, so it cannot change a sample; the
+`__ssat` form is for cores that define `__ARM_FEATURE_SAT`. `audiodsp_sat16`, the same
+function for the shared C and the CPython extension, is unchanged.
+
+**What moved.** Two stored digests: `streaming_component`'s streaming half
+(`f3ffad8e…` to `33b27a2f…`) and `synthtools_acceptance` (`b6e3b06f…` to
+`757d944a…`; `lead`, `bend` and `bass`). Both were re-captured from the new
+oracle's output, and CPython, desktop MicroPython and the oracle agree on
+them. Every other stored digest held: `midi_component`, `effects_component`,
+`biquad_component`, `mixdown_knee`.
+
 ## Resynced with 11.0.0-alpha.1 (audiodsp#220)
 
 Every audio fix CircuitPython made between 10.3.0 and 11.0.0-alpha.1 is in
 this port now, and so is its one audio addition, `PitchShift.freeze`, which
 followed in audiodsp#222. The finalisers upstream gave every audio object
 are left out on purpose. What was taken, module by module, and what was left
-out is in [upstream-sync.md](upstream-sync.md#the-last-resync-1100-alpha1-audiodsp220).
+out is in [upstream-sync.md](upstream-sync.md#the-resync-before-1100-alpha1-audiodsp220).
 
 It retires five differences recorded below, because upstream now does the
 same: the stream I/O in `WaveFile` and `synthio.from_file` (upstream switched
@@ -241,6 +292,9 @@ in audiocomponents' parity sequences on CPython and on MicroPython.
 
 ## The oracle is CircuitPython 11.0.0-alpha.1 (audiodsp#201)
 
+> The oracle has moved on to 11.0.0-alpha.2, see
+> [above](#resynced-with-1100-alpha2). This is how it got to alpha.1.
+
 The oracle moved from 10.3.0 to 11.0.0-alpha.1 (520805e12) on 2026-10-08,
 with the binary at `bin/circuitpython-oracle-11.0.0-alpha.1`
 (`CIRCUITPYTHON_ORACLE`, `tests/test_voice_ceiling_consistency.py`). It moved
@@ -1950,17 +2004,21 @@ peaking-EQ fix below let it drop the Mixer entirely.)
 
 ## A voice at level 1.0 is a wire (audiodsp#95)
 
-Upstream maps a voice level of 1.0 to Q15 **32768**:
+> **Upstream since 11.0.0-alpha.2** (11a329885, fc57c0f36), so no longer a
+> deviation from the oracle. The unity branch described below is gone from
+> this port; what is left is the record of what was wrong.
+
+Upstream mapped a voice level of 1.0 to Q15 **32768**:
 
 ```c
 uint16_t level = (uint16_t)(synthio_block_slot_get_limited(
     &voice->level, 0.0, 1.0) * (1 << 15));
 ```
 
-and then scales by `level / 32767.0f` in `mult16signed`. So "unity" is really
-**1.0000305**, and every sample whose magnitude reaches 32736 comes out one
-LSB larger — away from zero — with 32767 clamping. A voice at level 1.0 is
-not a wire, and never was.
+and then scaled by `level / 32767.0f` in `mult16signed`. So "unity" was really
+**1.0000305**, and every sample whose magnitude reached 32736 came out one
+LSB larger, away from zero, with 32767 clamping. A voice at level 1.0 was
+not a wire.
 
 Measured here on the full int16 range, once per value, through a one-voice
 Mixer with the level gate opened on a leading block of silence:
@@ -1970,38 +2028,15 @@ channels=1: 63 samples differ, |value| >= 32736, deltas [-1, 1], channel index [
 channels=2: 63 samples differ, |value| >= 32736, deltas [-1, 1], channel index [1]
 ```
 
-Stereo differs on the right channel only, because a voice at panning 0 gets
-`32767 - panning` on the left and a flat `32768` on the right: the left
-scale's quotient is 32767/32767, which is exactly one, and only the right
-carries the lifted multiplier. Mono takes the right-hand path on both.
-
-**The deviation.** A multiplier of exactly `1 << 15` means unity and passes
-the sample through, in `mult16signed` (`src/audiomixer/Mixer.c`) and in
-`_mod_mul` (`src/cpython/audiomixer.py`). Every other level is upstream's
-arithmetic bit for bit — the single-precision quotient and product that
-audiodsp#84 pinned, which `tests/test_cpython_audiomixer_level.py` still
-enumerates over Q15 0..32767.
-
-**Why deviate rather than route around it.** Answer (1) on the issue — a
-class claiming a wire at Mix 0 routes through no mixer — is what the shipped
-effect classes took, and five of them were rewired for it. That fixed the
-classes; it did not fix `audiomixer`, and the next class to put a full-scale
-signal through a level-1.0 voice would have found it again. The scale is one
-number in one kernel and the fix is one compare, so the module now means what
-it says.
-
-**What moved.** Nothing any committed gate covers: `verify_acceptance`,
-`verify_effects`, `verify_streaming`, `verify_biquad` and
-`verify_mixdown_knee` all match their recorded hashes unchanged, because none
-of their material carries a full-scale sample through a level-1.0 voice. What
-does move is any render that does — by one LSB, on samples at |value| >= 32736
-only, and toward the sample's own value rather than away from it.
-
-**Not applied to the CircuitPython target,** per the standing rule: the oracle
-keeps upstream's arithmetic, so this is one of the enumerated places where our
-targets and the oracle disagree by design. A parity script that renders
-full-scale material through a level-1.0 voice will see it, and should expect
-it.
+Stereo differed on the right channel only, because a voice at panning 0 got
+`32767 - panning` on the left and a flat `32768` on the right.
+
+This port answered with a branch: a multiplier of exactly `1 << 15` passed
+the sample through, in `mult16signed` and in `_mod_mul`. Upstream's answer, in
+11.0.0-alpha.2, is to change the arithmetic: a sample is `(x * level) >> 15`,
+and a centred pan is `32768 - panning`, so level 1.0 at pan 0 is 32768 on both
+channels and the product is the sample itself. See
+[Resynced with 11.0.0-alpha.2](#resynced-with-1100-alpha2).
 
 ## Peaking EQ computed `b2` with the wrong sign (effects-extension tier)
 

docs/upstream-sync.md

@@ -63,7 +63,38 @@ to turn up.
 7. Update the record below: what was taken, what was held back, and any
    difference that a fix retired or added.
 
-## The last resync: 11.0.0-alpha.1 (audiodsp#220)
+## The last resync: 11.0.0-alpha.2
+
+The pin moved from 11.0.0-alpha.1 to 11.0.0-alpha.2 (d53b2277c). Between the
+two, upstream touched the ported modules in three commits, all in `audiomixer`
+and `synthio_sat16`; nothing else in the eight modules changed, and `lib/mp3`
+is the same commit (aac02afd9f) as at the pin.
+
+- **audiomixer** (11a329885, fc57c0f36). A voice is scaled in integers:
+  `(ai * mul) >> 15`, where it was `ai * (mul / 32767.0f)` truncated toward
+  zero, and a centred pan is `32768 - panning`. Taken in upstream's words in
+  `src/audiomixer/Mixer.c`, in the CPython extension's scaling kernel and in
+  `src/cpython/audiomixer.py`. Every level below 1.0 moves by up to one LSB,
+  and a small negative sample now rounds down (-1 at level 0.5 stays -1). The
+  ARM `smulwb` path and the `__ARM_FEATURE_DSP` guards are not here, as before:
+  this port's `mult16signed` is the portable C, which upstream says gives the
+  same bytes.
+- **synthio** (cbbde1208). `synthio_sat16` is inline in `src/synthio/__init__.h`
+  as upstream has it, with the `__ssat` form on cores that define
+  `__ARM_FEATURE_SAT`. It cannot change a sample.
+
+`mixer_q15_level_probe.py` covers the mixer in `verify_dsp.py`, where
+CircuitPython, MicroPython and CPython print the same bytes, and a build from
+before the change prints different ones. Two stored digests moved, both
+re-captured from the alpha.2 oracle's output: the streaming half of
+`streaming_component`, and `synthtools_acceptance`. The rest held, and so did
+audiocomponents' instrument parity sequences on CPython and on MicroPython.
+
+**A difference retired:** a voice at level 1.0 is a wire (audiodsp#95).
+Upstream's arithmetic makes it so, and the unity branch in `mult16signed` is
+deleted. It also retires the left-below-right pan asymmetry at pan 0.
+
+## The resync before: 11.0.0-alpha.1 (audiodsp#220)
 
 The pin moved from 10.3.0 to 11.0.0-alpha.1 with audiodsp#201, which took
 6dddbda87 (buffer lengths and silence fills) and nothing else. audiodsp#220
@@ -198,8 +229,6 @@ reason, and a resync should not take them.
 - **audiomixer**: a reset keeps every voice playing where it was instead of
   stopping them
   ([why](upstream-diff.md#resetting-a-mixer-silenced-it-permanently-audioeffects-tier)).
-  A voice at level 1.0 is a wire
-  ([why](upstream-diff.md#a-voice-at-level-10-is-a-wire-audiodsp95)).
   A looping sample under one word is refused
   ([why](upstream-diff.md#audiomixer-a-looping-sample-under-one-word-is-refused-not-spun-on-audiodsp85)).
   Level and panning are always block inputs, and the ARM CMSIS intrinsics are

src/audiomixer/Mixer.c

@@ -264,24 +264,11 @@ static inline uint32_t add16signed(uint32_t a, uint32_t b) {
     return result;
 }
 
-// Deviation from upstream: a multiplier of 1<<15 is unity, and passes the
-// sample through. Upstream maps a voice level of 1.0 to Q15 32768 and then
-// scales by `level / 32767.0f`, so unity is really 1.0000305 and every
-// sample at |value| >= 32736 comes out one LSB larger. See
-// docs/upstream-diff.md, "A voice at level 1.0 is a wire". Only the unity
-// multiplier takes this branch; every other level is upstream's arithmetic,
-// bit for bit.
 static inline uint32_t mult16signed(uint32_t val, int32_t lomul, int32_t himul) {
     uint32_t result = 0;
     for (int8_t i = 0; i < 2; i++) {
-        int32_t mul = i ? himul : lomul;
         int16_t ai = (val >> (sizeof(uint16_t) * 8 * i));
-        if (mul == (1 << 15)) {
-            result |= (((uint32_t)ai) & 0xffff) << (sizeof(int16_t) * 8 * i);
-            continue;
-        }
-        float mod_mul = (float)mul / (float)((1 << 15) - 1);
-        int32_t intermediate = (int32_t)(ai * mod_mul);
+        int32_t intermediate = (ai * (i ? himul : lomul)) >> 15;
         if (intermediate > SHRT_MAX) {
             intermediate = SHRT_MAX;
         } else if (intermediate < SHRT_MIN) {
@@ -430,9 +417,9 @@ static void mix_down_one_voice(audiomixer_mixer_obj_t *self,
             // panning > 0 attenuates the LEFT channel. CircuitPython 10.3.0
             // flipped this and matched synthio.Note to it.
             if (panning >= 0) {
-                left_panning_scaled = 32767 - panning;
+                left_panning_scaled = 32768 - panning;
             } else {
-                right_panning_scaled = 32767 + panning;
+                right_panning_scaled = 32768 + panning;
             }
         }
 

src/cpython/_audiodsp.c

@@ -4538,17 +4538,9 @@ static PyObject *audiodsp_mix_s16(PyObject *module, PyObject *args) {
     return result;
 }
 
-/* One voice's level, as the single-precision multiplier the native mixer
- * uses: `(float)level / (float)32767`, with Q15 32768 (a level of 1.0) as an
- * exact 1.0. `_mod_mul` in audiomixer.py is the same arithmetic. */
-static float mixer_mod_mul(long level) {
-    if (level == 32768) return 1.0f;
-    return (float)level / (float)32767;
-}
-
 /* Scale a block of interleaved int16 pairs by a voice's per-channel level, the
  * loop `Mixer._get_buffer` runs in Python for any voice that is not at
- * unity: product in float32, truncation toward zero, clamp to int16. A level
+ * unity: `(sample * level) >> 15`, clamp to int16. A level
  * move (`pending`) lands at the first zero crossing, or is forced at each
  * index in `forced` (ascending sample indices, where a source stretch ends),
  * exactly as the Python loop does. */
@@ -4581,8 +4573,8 @@ static PyObject *audiodsp_scale_s16_levels(PyObject *module, PyObject *args) {
     int16_t *out = (int16_t *)PyBytes_AS_STRING(result);
     const Py_ssize_t count = data.len / 2;
     long active[2] = {active_lo, active_hi};
-    float mul_lo = mixer_mod_mul(active[0]);
-    float mul_hi = mixer_mod_mul(active[1]);
+    long mul_lo = active[0];
+    long mul_hi = active[1];
     int32_t last_lo = 0, last_hi = 0;
     Py_ssize_t next_forced = 0;
     for (Py_ssize_t index = 0; index < count; index += 2) {
@@ -4599,8 +4591,8 @@ static PyObject *audiodsp_scale_s16_levels(PyObject *module, PyObject *args) {
                 if (at == index && index) {
                     active[0] = pending_lo;
                     active[1] = pending_hi;
-                    mul_lo = mixer_mod_mul(active[0]);
-                    mul_hi = mixer_mod_mul(active[1]);
+                    mul_lo = active[0];
+                    mul_hi = active[1];
                     last_lo = last_hi = 0;
                 }
                 break;
@@ -4615,18 +4607,18 @@ static PyObject *audiodsp_scale_s16_levels(PyObject *module, PyObject *args) {
                     && ((last_lo < 0) != (lo < 0) || (last_hi < 0) != (hi < 0)))) {
                 active[0] = pending_lo;
                 active[1] = pending_hi;
-                mul_lo = mixer_mod_mul(active[0]);
-                mul_hi = mixer_mod_mul(active[1]);
+                mul_lo = active[0];
+                mul_hi = active[1];
             } else {
                 last_lo = lo;
                 last_hi = hi;
             }
         }
-        int32_t scaled = (int32_t)((float)lo * mul_lo);
+        int32_t scaled = (int32_t)((lo * mul_lo) >> 15);
         out[index] = (int16_t)(scaled > INT16_MAX ? INT16_MAX
                                : scaled < INT16_MIN ? INT16_MIN : scaled);
         if (index + 1 < count) {
-            scaled = (int32_t)((float)hi * mul_hi);
+            scaled = (int32_t)((hi * mul_hi) >> 15);
             out[index + 1] = (int16_t)(scaled > INT16_MAX ? INT16_MAX
                                        : scaled < INT16_MIN ? INT16_MIN : scaled);
         }