Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
---
libavradio/sdrdemux.c | 56 ++++++++++++++++++++-----------------------
1 file changed, 26 insertions(+), 30 deletions(-)
diff --git a/libavradio/sdrdemux.c b/libavradio/sdrdemux.c
index 7cc71b2cfb..92b218d899 100644
--- a/libavradio/sdrdemux.c
+++ b/libavradio/sdrdemux.c
@@ -616,43 +616,39 @@ static double find_am_carrier(SDRContext *sdr, const
AVComplexFloat *data, int d
}
/**
- * Demodulate with a carrier that is in the middle of the signal like in AM
- * This will normalize the signal based on the carrier amplitude and subtract
the carrier
+ * Demodulate with a carrier that is a N-th of the frequency.
+ * If N is one the carrier will be subtracted from the signal too.
+ * N==1 corresponds to classical AM, N>1 are demodulations with suppressed
carriers.
+ *
+ * For N==1 and N==3 the signal will be normalized. For N==2 it will not be
+ * This is to avoid a sqrt() and happens to be what we want in the current use
cases.
+ *
+ * The output will be scaled by the window.
*/
-static void synchronous_am_demodulation(AVComplexFloat *iblock, AVComplexFloat
*icarrier, float *window, int len)
+static av_always_inline void synchronous_am_demodulationN(AVComplexFloat
*iblock, AVComplexFloat *icarrier, float *window, int len, int N)
{
+ av_assert0(N>=1 && N<=3); //currently supported, trivial to add more if
needed
+
for (int i = 0; i<len; i++) {
AVComplexFloat c = icarrier[i];
AVComplexFloat s = iblock[i];
float w = window[i];
- float den = w / (c.re*c.re + c.im*c.im);
- av_assert0(c.re*c.re + c.im*c.im > 0);
+ AVComplexFloat c2= {c.re*c.re, c.im*c.im};
+ float den = w/(c2.re + c2.im);
+
+ if (N==2) {
+ c.im *= c.re + c.re;
+ c.re = c2.re - c2.im;
+ } else if (N==3) {
+ den *= den;
+ c.re *= c2.re - 3*c2.im;
+ c.im *= 3*c2.re - c2.im;
+ }
iblock[i].re = ( s.im*c.im + s.re*c.re) * den;
iblock[i].im = ( s.im*c.re - s.re*c.im) * den;
- iblock[i].re -= w;
- }
-}
-
-/**
- * Demodulate with a carrier that is half the frequency and reduced amplitude
- * This will not normalize the signal based on the carrier amplitude
- */
-static void synchronous_am_demodulation2(AVComplexFloat *iblock,
AVComplexFloat *icarrier, float *window, int len)
-{
- for (int i = 0; i<len; i++) {
- AVComplexFloat c = icarrier[i];
- AVComplexFloat s = iblock[i];
- AVComplexFloat c2;
- float w = window[i];
- float den = w / (c.re*c.re + c.im*c.im);
- av_assert0(c.re*c.re + c.im*c.im > 0);
-
- c2.re = c.re*c.re - c.im*c.im;
- c2.im = c.re*c.im + c.im*c.re;
-
- iblock[i].re = ( s.im*c2.im + s.re*c2.re) * den;
- iblock[i].im = ( s.im*c2.re - s.re*c2.im) * den;
+ if (N==1)
+ iblock[i].re -= w;
}
}
@@ -728,7 +724,7 @@ static int demodulate_am(SDRContext *sdr, int stream_index,
AVPacket *pkt)
sst->block[i] = sdr->block[index + i - len];
sst->ifft(sst->ifft_ctx, sst->icarrier, sst->block,
sizeof(AVComplexFloat));
- synchronous_am_demodulation(sst->iblock, sst->icarrier, sst->window,
2*sst->block_size);
+ synchronous_am_demodulationN(sst->iblock, sst->icarrier, sst->window,
2*sst->block_size, 1);
scale = 0.9;
} else {
// Synchronous demodulation using Macleod based systhesized carrier
@@ -997,7 +993,7 @@ static int demodulate_fm(SDRContext *sdr, int stream_index,
AVPacket *pkt)
apply_deemphasis(sdr, sst->block + i + 2*carrier19_i - 2*shift,
sst->block_size_p2, sample_rate_p2, + 1);
apply_deemphasis(sdr, sst->block + i + 2*carrier19_i - 2*shift,
sst->block_size_p2, sample_rate_p2, - 1);
sst->ifft_p2(sst->ifft_p2_ctx, sst->iside , sst->block + i,
sizeof(AVComplexFloat));
- synchronous_am_demodulation2(sst->iside, sst->icarrier,
sst->window_p2, 2*sst->block_size_p2);
+ synchronous_am_demodulationN(sst->iside, sst->icarrier,
sst->window_p2, 2*sst->block_size_p2, 2);
}
memset(sst->block + len17_i, 0, (2*sst->block_size_p2 - len17_i) *
sizeof(AVComplexFloat));
apply_deemphasis(sdr, sst->block, 2*sst->block_size_p2, sample_rate_p2, +
1);
--
2.31.1
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