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SoftFM
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Stereo decoding works. WHEEE!!

This commit is contained in:
Joris van Rantwijk 2013-12-31 00:56:53 +01:00
parent 351e22f9bb
commit cecf407d00
2 changed files with 74 additions and 12 deletions
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75
FmDecode.cc
View File

@ -274,10 +274,13 @@ FmDecoder::FmDecoder(double sample_rate_if,
// Construct HighPassFilterIir
, m_dcblock_mono(30.0 / sample_rate_pcm)
, m_dcblock_stereo(30.0 / sample_rate_pcm)
// Construct LowwPassFilterRC
, m_deemph_mono((deemphasis == 0) ?
1.0 : (deemphasis * sample_rate_pcm * 1.0e-6))
, m_deemph_mono(
(deemphasis == 0) ? 1.0 : (deemphasis * sample_rate_pcm * 1.0e-6))
, m_deemph_stereo(
(deemphasis == 0) ? 1.0 : (deemphasis * sample_rate_pcm * 1.0e-6))
{
// nothing more to do
@ -325,22 +328,37 @@ void FmDecoder::process(const IQSampleVector& samples_in,
m_pilotpll.process(m_buf_baseband, m_buf_rawstereo);
m_stereo_detected = m_pilotpll.locked();
if (m_stereo_enabled) {
// Demodulate stereo signal.
demod_stereo(m_buf_baseband, m_buf_rawstereo);
// Demodulate stereo signal.
demod_stereo(m_buf_baseband, m_buf_rawstereo);
// Extract audio and downsample.
// NOTE: This MUST be done even if no stereo signal is detected yet,
// because the downsamplers for mono and stereo signal must be
// kept in sync.
m_resample_stereo.process(m_buf_rawstereo, m_buf_stereo);
// Extract audio and downsample.
m_resample_stereo.process(m_buf_rawstereo, m_buf_stereo);
// DC blocking and de-emphasis.
m_dcblock_stereo.process_inplace(m_buf_stereo);
m_deemph_stereo.process_inplace(m_buf_stereo);
// TODO : filters
if (m_stereo_detected) {
// Extract left/right channels from mono/stereo signals.
stereo_to_left_right(m_buf_mono, m_buf_stereo, audio);
} else {
// Duplicate mono signal in left/right channels.
mono_to_left_right(m_buf_mono, audio);
}
} else {
// Just return mono channel.
audio = move(m_buf_mono);
}
// TODO : stereo mixing
audio = move(m_buf_mono);
}
@ -360,4 +378,37 @@ void FmDecoder::demod_stereo(const SampleVector& samples_baseband,
}
}
// Duplicate mono signal in left/right channels.
void FmDecoder::mono_to_left_right(const SampleVector& samples_mono,
SampleVector& audio)
{
unsigned int n = samples_mono.size();
audio.resize(2*n);
for (unsigned int i = 0; i < n; i++) {
Sample m = samples_mono[i];
audio[2*i] = m;
audio[2*i+1] = m;
}
}
// Extract left/right channels from mono/stereo signals.
void FmDecoder::stereo_to_left_right(const SampleVector& samples_mono,
const SampleVector& samples_stereo,
SampleVector& audio)
{
unsigned int n = samples_mono.size();
assert(n == samples_stereo.size());
audio.resize(2*n);
for (unsigned int i = 0; i < n; i++) {
Sample m = samples_mono[i];
Sample s = samples_stereo[i];
audio[2*i] = m + s;
audio[2*i+1] = m - s;
}
}
/* end */

11
FmDecode.h
View File

@ -168,6 +168,15 @@ private:
void demod_stereo(const SampleVector& samples_baseband,
SampleVector& samples_stereo);
/** Duplicate mono signal in left/right channels. */
void mono_to_left_right(const SampleVector& samples_mono,
SampleVector& audio);
/** Extract left/right channels from mono/stereo signals. */
void stereo_to_left_right(const SampleVector& samples_mono,
const SampleVector& samples_stereo,
SampleVector& audio);
// Data members.
const double m_sample_rate_if;
const double m_sample_rate_baseband;
@ -196,7 +205,9 @@ private:
DownsampleFilter m_resample_mono;
DownsampleFilter m_resample_stereo;
HighPassFilterIir m_dcblock_mono;
HighPassFilterIir m_dcblock_stereo;
LowPassFilterRC m_deemph_mono;
LowPassFilterRC m_deemph_stereo;
};
#endif