From ffe78ae105e481e0268f823e267f60f1d7c4b1a6 Mon Sep 17 00:00:00 2001
From: John Greb <hexameron@spam.no>
Date: Mon, 10 Nov 2014 10:14:07 +0000
Subject: [PATCH] Fractional resampling.

---
 CMakeLists.txt                   |  1 -
 plugins/channel/CMakeLists.txt   |  6 ++---
 plugins/channel/usb/usbdemod.cpp | 44 ++++++++++++++++++++++++++------
 plugins/channel/usb/usbdemod.h   |  2 +-
 4 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 051c303d0..8abc6a808 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -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)
 
diff --git a/plugins/channel/CMakeLists.txt b/plugins/channel/CMakeLists.txt
index ac8f1bec8..b16491325 100644
--- a/plugins/channel/CMakeLists.txt
+++ b/plugins/channel/CMakeLists.txt
@@ -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)
diff --git a/plugins/channel/usb/usbdemod.cpp b/plugins/channel/usb/usbdemod.cpp
index 8906869c1..c563ba978 100644
--- a/plugins/channel/usb/usbdemod.cpp
+++ b/plugins/channel/usb/usbdemod.cpp
@@ -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();
diff --git a/plugins/channel/usb/usbdemod.h b/plugins/channel/usb/usbdemod.h
index 4abf10730..c938fe659 100644
--- a/plugins/channel/usb/usbdemod.h
+++ b/plugins/channel/usb/usbdemod.h
@@ -26,7 +26,7 @@
 #include "audio/audiofifo.h"
 #include "util/message.h"
 
-#define usbFftLen 1024
+#define USBFFTLEN 2048
 
 class AudioFifo;