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POCSAG Squelch and Filtering (#1424)

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* Disable audio processing when not using squelch
* Add 2k4 lowpass fitler for 24Khz audio for POCSAG
This commit is contained in:
Kyle Reed 2023-08-30 10:24:35 -07:00 committed by GitHub
parent f46e20c977
commit 07be74701f
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 18 additions and 7 deletions
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17
firmware/baseband/proc_pocsag.cpp
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@ -33,8 +33,6 @@
#include <cstddef>
void POCSAGProcessor::execute(const buffer_c8_t& buffer) {
// This is called at 1500Hz
if (!configured) return;
// Get 24kHz audio
@ -43,12 +41,14 @@ void POCSAGProcessor::execute(const buffer_c8_t& buffer) {
const auto channel_out = channel_filter.execute(decim_1_out, dst_buffer);
auto audio = demod.execute(channel_out, audio_buffer);
// Output audio pre-smoothing so squelch actually works.
// NB: It's useful to output *after* when debugging the smoothing filter.
// When use_squelch_ is true, AudioOutput applies filters
// which should eliminate the need to do this smoothing.
if (use_squelch_ == false)
smooth.Process(audio.p, audio.count);
// NB: This applies audio filters in-place when use_squelch_ is true.
audio_output.write(audio);
// Smooth the data to make decoding more accurate.
smooth.Process(audio.p, audio.count);
processDemodulatedSamples(audio.p, 16);
extractFrames();
}
@ -83,10 +83,13 @@ void POCSAGProcessor::on_message(const Message* const message) {
case Message::ID::NBFMConfigure: {
auto config = reinterpret_cast<const NBFMConfigureMessage*>(message);
use_squelch_ = config->squelch_level > 0;
audio_output.configure(
audio_24k_hpf_300hz_config,
audio_8k_deemph_300_6_config,
audio_24k_lpf_2400hz_config,
config->squelch_level / 100.0);
audio_output.configure(use_squelch_);
break;
}

2
firmware/baseband/proc_pocsag.hpp
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@ -215,6 +215,8 @@ class POCSAGProcessor : public BasebandProcessor {
int m_numCode{0};
bool m_inverted{false};
bool use_squelch_ = false;
/* NB: Threads should be the last members in the class definition. */
BasebandThread baseband_thread{baseband_fs, this, baseband::Direction::Receive};
RSSIThread rssi_thread{};

6
firmware/common/dsp_iir_config.hpp
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@ -77,6 +77,12 @@ constexpr iir_biquad_config_t audio_24k_deemph_300_6_config{
{0.03780475f, 0.03780475f, 0.00000000f},
{1.00000000f, -0.92439049f, 0.00000000f}};
// scipy.signal.butter(1, 2400 / 12000.0, 'lowpass', analog=False)
// NOTE: Technically, order-1 filter, b[2] = a[2] = 0.
constexpr iir_biquad_config_t audio_24k_lpf_2400hz_config{
{0.03780475f, 0.03780475f, 0.00000000f},
{1.00000000f, -0.92439049f, 0.00000000f}};
// scipy.signal.butter(1, 300 / 8000.0, 'lowpass', analog=False)
// NOTE: Technically, order-1 filter, b[2] = a[2] = 0.
constexpr iir_biquad_config_t audio_16k_deemph_300_6_config{