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Fractional resampling.

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This commit is contained in:
John Greb 2014-11-10 10:14:07 +00:00
parent f793f635af
commit ffe78ae105
4 changed files with 39 additions and 14 deletions
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1
CMakeLists.txt
View File

@ -1,7 +1,6 @@
cmake_minimum_required(VERSION 2.8.9)
option(KERNEL "Use Linux Kernel Video4Linux Source." OFF)
option(IS96KHZ "Upper SideBand decoder needs 96kHz" OFF)
list(APPEND CMAKE_MODULE_PATH ${CMAKE_SOURCE_DIR}/cmake/Modules)

6
plugins/channel/CMakeLists.txt
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@ -1,10 +1,8 @@
project(demod)
add_subdirectory(nfm)
add_subdirectory(tcpsrc)
add_subdirectory(ssb)
add_subdirectory(tcpsrc)
add_subdirectory(usb)
if (IS96KHZ)
add_subdirectory(usb)
endif()
#add_subdirectory(tetra)

44
plugins/channel/usb/usbdemod.cpp
View File

@ -37,7 +37,7 @@ USBDemod::USBDemod(AudioFifo* audioFifo, SampleSink* sampleSink) :
m_audioBufferFill = 0;
m_undersampleCount = 0;
USBFilter = new fftfilt(0.01, m_Bandwidth / 96000.0, usbFftLen);
USBFilter = new fftfilt(0.01, m_Bandwidth / 96000.0, USBFFTLEN);
// if (!USBFilter) segfault;
}
@ -52,7 +52,24 @@ void USBDemod::configure(MessageQueue* messageQueue, Real Bandwidth, Real volume
cmd->submit(messageQueue, this);
}
/* Expects samplerate as multiples of 96kHz. */
/* Fractional Downsample to 48 kHz.
* 192 1:4 (3072 / 16)
* 144 1:3 (2304 / 16)
* 96 1:2 (1536 / 16)
* 72 2:3 ( 288 / 4)
* 64 3:4 (1024 / 16)
* For Arbritrary resample use ssb demodulator */
double rerate(int rate)
{
switch (rate)
{
case 64000 : return (3.0 * 64000); break;
case 72000 : return (2.0 * 72000); break;
case 0 : return (1.0 ) ; break;
default : return (1.0 * rate ); break;
}
}
void USBDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iterator end, bool positiveOnly)
{
Real a, b;
@ -60,17 +77,24 @@ void USBDemod::feed(SampleVector::const_iterator begin, SampleVector::const_iter
int n_out;
cmplx *sideband;
bool consumed;
int samplestep = m_sampleRate / 96000;
int samplestep = 2;
if (samplestep < 1 )
samplestep = 1;
for(SampleVector::const_iterator it = begin; it < end; it += samplestep) {
if ((m_sampleRate == 72000)||(m_sampleRate == 144000))
samplestep = 3; // !! FFT buffer length is a power of two
if ((m_sampleRate == 64000)||(m_sampleRate == 192000))
samplestep = 4; // buffer length should be good
for(SampleVector::const_iterator it = begin; it < end; it ++) {
a = it->real();
b = it->imag();
c = Complex(a / 65536.0, b / 65536.0);
n_out = USBFilter->run(c, &sideband, true);
for (int i = 0; i < n_out; i+=2) {
if (m_sampleRate <= 72000)
n_out += USBFilter->run(c, &sideband, true);
if (m_sampleRate == 64000)
n_out += USBFilter->run(c, &sideband, true);
for (int i = 0; i < n_out; i += samplestep) {
Real demod = (sideband[i].real() + sideband[i].imag()) * 32768.0;
// Downsample by 4x for audio display
@ -106,15 +130,19 @@ void USBDemod::stop()
bool USBDemod::handleMessage(Message* cmd)
{
double rate;
if(DSPSignalNotification::match(cmd)) {
DSPSignalNotification* signal = (DSPSignalNotification*)cmd;
m_sampleRate = signal->getSampleRate();
rate = rerate(m_sampleRate);
USBFilter->create_filter(300.0 / rate, (double)m_Bandwidth / rate);
cmd->completed();
return true;
} else if(MsgConfigureUSBDemod::match(cmd)) {
MsgConfigureUSBDemod* cfg = (MsgConfigureUSBDemod*)cmd;
m_Bandwidth = cfg->getBandwidth();
USBFilter->create_filter(0.3 / 96.0, m_Bandwidth / 96000.0);
rate = rerate(m_sampleRate);
USBFilter->create_filter(300.0 / rate, (double)m_Bandwidth / rate);
m_volume = cfg->getVolume();
m_volume *= m_volume * 0.1;
cmd->completed();

2
plugins/channel/usb/usbdemod.h
View File

@ -26,7 +26,7 @@
#include "audio/audiofifo.h"
#include "util/message.h"
#define usbFftLen 1024
#define USBFFTLEN 2048
class AudioFifo;