Model the pair on fmd.c / fmmod.c, but with the parts that a 75 kHz
deviation forces:
- the demodulator discriminates with arg(x[n] * conj(x[n-1])) rather
than a PLL; an omegaN in the tens of kHz cannot track 75 kHz.
- emphasis is a one-pole RC (tau 75 us) on both ends, not fmd's 1/f
fc_impulse FIR. A 1/f FIR from f_low = 20 Hz would sit ~+57 dB at
20 Hz, where broadcast FM specifies flat below the corner.
- TXA_WFM leaves the shared preemph block off; wfmmod carries its own.
- wfmmod clamps bp_fc = deviation + f_high to 0.45 * samplerate, since
+/-90 kHz exceeds Nyquist at the rates the narrowband modes use.
Scope is mono: no 19 kHz pilot, no 38 kHz stereo subcarrier, no RDS.
Both mode enums are appended to so the ABI stays stable for clients.
The JNI bindings are deliberately left alone.
Verified against a wfmmod -> wfmd loopback: the discriminator is exact,
the dc-removal one-pole tracks |H_lp(f)| * ain * sdelta to ratio 1.000,
and a 700 + 1900 Hz two-tone comes back with THD+N ~ 3e-5 % at +/-37.5
kHz deviation. Note the demodulator aliases unless samplerate exceeds
2 * deviation * |aud|max, so 192 kHz is the practical floor.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Remove hardcoded /home/vladimir and /opt paths. NDK is now resolved via
ANDROID_NDK_HOME, ANDROID_SDK_ROOT/ANDROID_HOME, or the default SDK
location for Linux/macOS (latest version picked automatically). javac is
resolved via JAVA_HOME, system PATH, or Android Studio JBR on Linux/macOS.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Untrack all .o and .a files under third_party/ (rnnoise, libspecbleach)
- Add third_party/**/*.o and third_party/**/*.a to .gitignore
- Fix FFTW configure cross-compilation: add $(strip ...) around fftw_host
macro call and explicit --build flag so configure detects cross-compile
correctly (GNU make backslash-continuation in define blocks inserts a
leading space, causing --host= arm-... to be parsed as empty --host)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Makefile.android now downloads fftw-3.3.11.tar.gz automatically instead
of requiring the user to place sources in third_party/fftw/ manually.
The FFTW_SRC variable can still be overridden to use an existing copy.
Added distclean target. Updated README accordingly.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Uladzimir Karpenka
vladimir