OscillatorNode silent above ~9.5 kHz on Android devices where PROPERTY_OUTPUT_SAMPLE_RATE is 24 kHz

[spikything]

Description

OscillatorNode produces no audio (or severe rolloff starting ~9.5 kHz) for frequencies
above ~9.5 kHz on Android devices where PROPERTY_OUTPUT_SAMPLE_RATE is 24 kHz
(tested Huawei Nova 3i Android 9, Samsung Galaxy S22+ Android 16).

Root cause is in PeriodicWave::getPeriodicWaveSize()
(common/cpp/audioapi/core/effects/PeriodicWave.cpp):

if (sampleRate_ <= 24000) {
    return 2048;   // Nyquist = 12 kHz; band-limiting culls from ~9.5 kHz
}

When AudioContext is created without an explicit sampleRate, the library falls back to
AudioManager.getDevicePreferredSampleRate(), which reads PROPERTY_OUTPUT_SAMPLE_RATE.
On affected devices this returns 24000, so BaseAudioContext::sampleRate_ = 24000 and
getPeriodicWaveSize() returns 2048 (not 4096). The smaller table cap causes
getMaxNumberOfPartials() = 1024, leaving ~1 partial at 9.5 kHz and 0 at 12 kHz.

Expected: audio at 9.5–12 kHz is audible when the device preferred sample rate is 24000.
Actual: silent above ~12 kHz, severe rolloff from ~9.5 kHz.

Fix: change <= to < in getPeriodicWaveSize() so that exactly-24000 Hz
gets the 4096-entry table. PR to follow.

Steps to reproduce

1. On an affected device, create an AudioContext without specifying sampleRate:
   const ctx = new AudioContext();
2. Confirm ctx.sampleRate === 24000
3. Create an OscillatorNode, sweep frequency from 9000-12000 Hz,
   connect to destination, call start()
4. Observe: rolloff from ~9.5 kHz, silence at 12 kHz

Snack or a link to a repository

https://gist.github.com/spikything/5d549db6ad7872482ef26992e60a1109

React Native Audio API version

0.12.2

React Native version

0.81.5

Platforms

Android

JavaScript runtime

Hermes

Workflow

Expo Dev Client

Architecture

Fabric (New Architecture)

Build type

Release app & production bundle

Device

Real device

Device model

Huawei Nova 3i (Android 9), Samsung Galaxy S22+ (Android 16)

Acknowledgements

Yes

[mdydek]

@spikything To be honest I'm not in favor of this change: https://github.com/WebKit/WebKit/blob/fbd06f9be9076f8c623add8448271c98ef6076ec/Source/WebCore/Modules/webaudio/PeriodicWave.cpp#L330 <- here you have webkit code snippet (engine code behind safari), they also have <= when they are choosing size. Is there a reason why you do not want to manually increase context's sample rate to 48khz or 44.1? everything should be up sampled and be working just ok

[spikything]

@mdydek thanks for the quick response :) we're already passing { sampleRate: 48000 } to AudioContext - the issue is that Oboe ignores the requested rate on these devices and opens the stream at 24 kHz. ctx.sampleRate reads back 24000, not 48000, so PeriodicWave builds its tables for 24 kHz regardless of what we pass in js.

The hardware is definitely capable: on the same affected devices I tested (Huawei Nova 3i, Samsung Galaxy S22+), writing a 44100 Hz WAV and playing it via Android's AudioTrack (through expo-audio / ExoPlayer) produces tones up to 20 kHz with no issues (that's actually what I'm doing in my app now, verified the tones with a spectrum analyzer).

The limitation is specific to how the Oboe stream is initialized in react-native-audio-api, not the device hardware.

Would a fix that reads back the actual Oboe stream sample rate (via stream->getSampleRate()) and passes it to PeriodicWave (rather than the requested rate) be acceptable? That way, the table size would reflect what Oboe actually opened... and if Oboe does honour 48 kHz, then the full range is available. Happy to update the PR if so.

[mdydek]

okay, that's the more important issue for sure that oboe do not respect our custom sample rate, will check it out soon and return with more detailed plan how to approach it

[mdydek]

@spikything turned out it wasn't bug in the oboe, it was affecting both of the platforms and it was caused by wrong calculations of frequencies above 12khz

[spikything]

@mdydek good work hunting that one down - I thought I was going deaf, which is why I recruited my spectrum analyser app (and another old Flash-based app I created to verify that my mic can discern up to 20 kHz :)