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AudioFlinger: improve optimized audio scaling

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This commit is contained in:
Thomas Farstrike
2025-12-09 12:42:01 +01:00
parent 91127dfadd
commit b9e5f0d475
3 changed files with 37 additions and 82 deletions
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CHANGELOG.md
+4
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@@ -1,3 +1,7 @@
0.5.2
=====
- AudioFlinger: optimize WAV volume scaling
0.5.1
=====
- Fri3d Camp 2024 Board: add startup light and sound
internal_filesystem/lib/mpos/audio/stream_wav.py
+31 -81
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@@ -3,6 +3,7 @@
# Ported from MusicPlayer's AudioPlayer class
import machine
import micropython
import os
import time
import sys
@@ -10,7 +11,6 @@ import sys
# Volume scaling function - Viper-optimized for ESP32 performance
# NOTE: The line below is automatically commented out by build_mpos.sh during
# Unix/macOS builds (cross-compiler doesn't support Viper), then uncommented after build.
import micropython
@micropython.viper
def _scale_audio(buf: ptr8, num_bytes: int, scale_fixed: int):
"""Fast volume scaling for 16-bit audio samples using Viper (ESP32 native code emitter)."""
@@ -28,99 +28,46 @@ def _scale_audio(buf: ptr8, num_bytes: int, scale_fixed: int):
buf[i] = sample & 255
buf[i + 1] = (sample >> 8) & 255
import micropython
@micropython.viper
def _scale_audio_optimized(buf: ptr8, num_bytes: int, scale_fixed: int):
"""
Very fast 16-bit volume scaling using only shifts + adds.
- 100 % and above → no change
- < ~12.5 % → pure right-shift (fastest)
- otherwise → high-quality shift/add approximation
"""
if scale_fixed >= 32768: # 100 % or more
if scale_fixed >= 32768:
return
if scale_fixed <= 0: # muted
if scale_fixed <= 0:
for i in range(num_bytes):
buf[i] = 0
return
# --------------------------------------------------------------
# Very low volumes → simple right-shift (super cheap)
# --------------------------------------------------------------
if scale_fixed < 4096: # < ~12.5 %
shift: int = 0
tmp: int = 32768
while tmp > scale_fixed:
shift += 1
tmp >>= 1
for i in range(0, num_bytes, 2):
lo: int = int(buf[i])
hi: int = int(buf[i + 1])
s: int = (hi << 8) | lo
if hi & 128: # sign extend
s -= 65536
s >>= shift
buf[i] = s & 255
buf[i + 1] = (s >> 8) & 255
return
mask: int = scale_fixed
# --------------------------------------------------------------
# Medium → high volumes: sample * scale_fixed // 32768
# approximated with shifts + adds only
# --------------------------------------------------------------
# Build a 16-bit mask:
# bit 0 → add (s >> 15)
# bit 1 → add (s >> 14)
# ...
# bit 15 → add s (>> 0)
mask: int = 0
bit_value: int = 16384 # starts at 2^-1
remaining: int = scale_fixed
shift_idx: int = 1 # corresponds to >>1
while bit_value > 0:
if remaining >= bit_value:
mask |= (1 << (16 - shift_idx)) # correct bit position
remaining -= bit_value
bit_value >>= 1
shift_idx += 1
# Apply the mask
for i in range(0, num_bytes, 2):
lo: int = int(buf[i])
hi: int = int(buf[i + 1])
s: int = (hi << 8) | lo
if hi & 128:
s -= 65536
s: int = int(buf[i]) | (int(buf[i+1]) << 8)
if s >= 0x8000:
s -= 0x10000
result: int = 0
if mask & 0x8000: result += s # >>0
if mask & 0x4000: result += (s >> 1)
if mask & 0x2000: result += (s >> 2)
if mask & 0x1000: result += (s >> 3)
if mask & 0x0800: result += (s >> 4)
if mask & 0x0400: result += (s >> 5)
if mask & 0x0200: result += (s >> 6)
if mask & 0x0100: result += (s >> 7)
if mask & 0x0080: result += (s >> 8)
if mask & 0x0040: result += (s >> 9)
if mask & 0x0020: result += (s >>10)
if mask & 0x0010: result += (s >>11)
if mask & 0x0008: result += (s >>12)
if mask & 0x0004: result += (s >>13)
if mask & 0x0002: result += (s >>14)
if mask & 0x0001: result += (s >>15)
r: int = 0
if mask & 0x8000: r += s
if mask & 0x4000: r += s>>1
if mask & 0x2000: r += s>>2
if mask & 0x1000: r += s>>3
if mask & 0x0800: r += s>>4
if mask & 0x0400: r += s>>5
if mask & 0x0200: r += s>>6
if mask & 0x0100: r += s>>7
if mask & 0x0080: r += s>>8
if mask & 0x0040: r += s>>9
if mask & 0x0020: r += s>>10
if mask & 0x0010: r += s>>11
if mask & 0x0008: r += s>>12
if mask & 0x0004: r += s>>13
if mask & 0x0002: r += s>>14
if mask & 0x0001: r += s>>15
# Clamp to 16-bit signed range
if result > 32767:
result = 32767
elif result < -32768:
result = -32768
if r > 32767: r = 32767
if r < -32768: r = -32768
buf[i] = result & 255
buf[i + 1] = (result >> 8) & 255
buf[i] = r & 0xFF
buf[i+1] = (r >> 8) & 0xFF
import micropython
@micropython.viper
def _scale_audio_rough(buf: ptr8, num_bytes: int, scale_fixed: int):
"""Rough volume scaling for 16-bit audio samples using right shifts for performance."""
@@ -375,9 +322,12 @@ class WAVStream:
# smaller chunk size means less jerks but buffer can run empty
# at 22050 Hz, 16-bit, 2-ch, 4096/4 = 1024 samples / 22050 = 46ms
# with rough volume scaling:
# 4096 => audio stutters during quasibird
# 8192 => no audio stutters and quasibird runs at ~16 fps => good compromise!
# 16384 => no audio stutters during quasibird but low framerate (~8fps)
# with optimized volume scaling:
# 8192 => no audio stutters and quasibird runs at ~12fps
chunk_size = 4096*2
bytes_per_original_sample = (bits_per_sample // 8) * channels
total_original = 0
scripts/install.sh
+2 -1
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@@ -47,6 +47,8 @@ fi
# The issue is that this brings all the .git folders with it:
#$mpremote fs cp -r apps :/
$mpremote fs cp -r lib :/
$mpremote fs mkdir :/apps
$mpremote fs cp -r apps/com.micropythonos.* :/apps/
find apps/ -maxdepth 1 -type l | while read symlink; do
@@ -59,7 +61,6 @@ done
#echo "Unmounting builtin/ so that it can be customized..." # not sure this is necessary
#$mpremote exec "import os ; os.umount('/builtin')"
$mpremote fs cp -r builtin :/
$mpremote fs cp -r lib :/
#$mpremote fs cp -r data :/
#$mpremote fs cp -r data/images :/data/