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Simple FM squelch.

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This commit is contained in:
Jared Boone 2015-07-20 09:34:24 -07:00
parent 876a591a66
commit d7cb2c5da4
1 changed files with 46 additions and 3 deletions
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49
firmware/baseband/main.cpp
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@ -335,6 +335,40 @@ private:
}
};
class FMSquelch {
public:
bool execute(buffer_s16_t audio) {
// TODO: No hard-coded array size.
std::array<int16_t, N> squelch_energy_buffer;
const buffer_s16_t squelch_energy {
squelch_energy_buffer.data(),
squelch_energy_buffer.size()
};
non_audio_hpf.execute(audio, squelch_energy);
uint64_t max_squared = 0;
for(const auto sample : squelch_energy_buffer) {
const uint64_t sample_squared = sample * sample;
if( sample_squared > max_squared ) {
max_squared = sample_squared;
}
}
return (max_squared < (threshold * threshold));
}
private:
static constexpr size_t N = 32;
static constexpr int16_t threshold = 3072;
// nyquist = 48000 / 2.0
// scipy.signal.iirdesign(wp=8000 / nyquist, ws= 4000 / nyquist, gpass=1, gstop=18, ftype='ellip')
IIRBiquadFilter non_audio_hpf {
{ 0.51891061f, -0.95714180f, 0.51891061f },
{ 1.0f , -0.79878302f, 0.43960231f }
};
};
static volatile bool channel_spectrum_request_update { false };
static std::array<complex16_t, 256> channel_spectrum;
static uint32_t channel_spectrum_sampling_rate { 0 };
@ -502,9 +536,17 @@ public:
* -> 48kHz int16_t[32] */
auto audio = demod.execute(channel, work_audio_buffer);
audio_hpf.execute_in_place(audio);
feed_audio_stats(audio);
fill_audio_buffer(audio);
static uint64_t audio_present_history = 0;
const auto audio_present = squelch.execute(audio);
audio_present_history = (audio_present_history << 1) | (audio_present ? 1 : 0);
if( audio_present_history ) {
audio_hpf.execute_in_place(audio);
feed_audio_stats(audio);
fill_audio_buffer(audio);
} else {
mute_audio();
}
}
private:
@ -517,6 +559,7 @@ private:
{ 0.93346032f, -1.86687724f, 0.93346032f },
{ 1.0f , -1.97730264f, 0.97773668f }
};
FMSquelch squelch;
};
class WidebandFMAudio : public BasebandProcessor {