Native real-time audio analysis module (iOS & Android)

Hi,
I’m looking for a freelance developer to help with a very specific technical task related to real-time audio processing on mobile.
I only need a standalone native audio module.

SCOPE
Build a native audio analysis layer for:

* iOS (Swift preferred)
* Android (Kotlin preferred)

The module will later be consumed by a React Native application.
UI, product design are out of scope.

REQUIRED FEATURES
1) Microphone input
* real-time audio capture
* low-latency configuration
* stable buffer delivery

2) Audio level measurement
* RMS + peak
* updated in real time
* indicative values (no certified SPL required)

3) FFT / Spectrum
* real-time FFT
* output magnitude array (e.g. 256 or 512 bins)
* refresh rate suitable for live visualization

4) Pitch detection
* real-time fundamental frequency estimation
* output frequency + cents deviation
* smoothing for stable readings


INTEGRATION
The native module should expose a simple, clean API usable from JavaScript, for example:
* startMic() / stopMic()
* onLevel(callback)
* onSpectrum(callback)
* onPitch(callback)

Thread safety and proper resource cleanup are expected.

DELIVERABLES
* Full source code for iOS and Android
* Clear build/setup instructions
* A simple demo or test screen proving:
* microphone input works
* live level updates
* live spectrum updates
* live pitch detection

All delivered code must be work-for-hire with full ownership transferred.

Please include in your reply
1. A short description of previous real-time audio work
2. Which pitch detection approach you would use
3. Expected timeline
4. Fixed price estimate, ideally split into milestones:
* mic + level
* spectrum
* pitch detection


Thanks,
Gabriel