From 2eac36bdc640115a53accccaa5049b78253a43ac Mon Sep 17 00:00:00 2001
From: drowe67 <drowe67@01035d8c-6547-0410-b346-abe4f91aad63>
Date: Thu, 10 May 2012 03:41:25 +0000
Subject: [PATCH] added a spruious 10 kHz signal to test 48 to 8 kHz
 downsampler, seems to work OK

git-svn-id: https://svn.code.sf.net/p/freetel/code@409 01035d8c-6547-0410-b346-abe4f91aad63
---
 codec2-dev/src/fdmdv.c      |  4 ++--
 codec2-dev/unittest/t48_8.c | 30 +++++++++++++++++++++++++-----
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/codec2-dev/src/fdmdv.c b/codec2-dev/src/fdmdv.c
index 2f7ab3c8..bb78ffac 100644
--- a/codec2-dev/src/fdmdv.c
+++ b/codec2-dev/src/fdmdv.c
@@ -1183,7 +1183,7 @@ void fdmdv_get_demod_stats(struct FDMDV *fdmdv, struct FDMDV_STATS *fdmdv_stats)
 
   n is the number of samples at the 8 kHz rate, there are FDMDV_OS*n samples
   at the 48 kHz rate.  A memory of FDMDV_OS_TAPS/FDMDV_OS samples is reqd for
-  in8k[] (see example).
+  in8k[] (see t48_8.c unit test as example).
 
   This is a classic polyphase upsampler.  We take the 8 kHz samples
   and insert (FDMDV_OS-1) zeroes between each sample, then
@@ -1220,7 +1220,7 @@ void fdmdv_8_to_48(float out48k[], float in8k[], int n)
  
   n is the number of samples at the 8 kHz rate, there are FDMDV_OS*n
   samples at the 48 kHz rate.  As above however a memory of
-  FDMDV_OS_TAPS samples is reqd for in48k[] (see example).
+  FDMDV_OS_TAPS samples is reqd for in48k[] (see t48_8.c unit test as example).
 
   Low pass filter the 48 kHz signal at 4 kHz using the same filter as
   the upsampler, then just output every FDMDV_OS-th filtered sample.
diff --git a/codec2-dev/unittest/t48_8.c b/codec2-dev/unittest/t48_8.c
index 236bb78f..e476d986 100644
--- a/codec2-dev/unittest/t48_8.c
+++ b/codec2-dev/unittest/t48_8.c
@@ -1,4 +1,20 @@
-/* Unit test for 48 to 8 kHz sample rate conversion functions */
+/* 
+   t48_8.c
+   David Rowe
+   May 10 2012
+
+   Unit test for 48 to 8 kHz sample rate conversion functions.  I
+   evaluated output by plotting using Octave and looking for jaggies:
+
+     pl("../unittest/out48.raw",1,3000)
+     pl("../unittest/out8.raw",1,3000)
+
+   Listening to it also shows up anything nasty:
+
+     $ play -s -2 -r 48000 out48.raw
+     $ play -s -2 -r 8000 out8.raw
+
+  */
 
 #include <assert.h>
 #include <stdlib.h>
@@ -25,7 +41,7 @@ int main() {
     short out8k_short[N8];
     FILE *f8;
 
-    int i,f,t;
+    int i,f,t,t1;
     float freq = 505.0;
 
     f48 = fopen("out48.raw", "wb");
@@ -40,7 +56,7 @@ int main() {
     for(i=0; i<FDMDV_OS_TAPS; i++)
 	in48k[i] = 0.0;
 
-    t = 0;
+    t = t1 = 0;
     for(f=0; f<FRAMES; f++) {
 
 #ifdef DC
@@ -64,10 +80,14 @@ int main() {
 	    out48k_short[i] = (short)out48k[i];
 	fwrite(out48k_short, sizeof(short), N48, f48);
 	
+	/* add a 10 kHz spurious signal for fun, we want down sampler to
+	   knock this out */
+
+	for(i=0; i<N48; i++,t1++)
+	    in48k[i+FDMDV_OS_TAPS] = out48k[i] + 16000.0*cos(TWO_PI*t1*1E4/FS);
+
 	/* downsample and update filter memory */
 
-	for(i=0; i<N48; i++)
-	    in48k[i+FDMDV_OS_TAPS] = out48k[i];
 	fdmdv_48_to_8(out8k, &in48k[FDMDV_OS_TAPS], N8);
 	for(i=0; i<FDMDV_OS_TAPS; i++)
 	    in48k[i] = in48k[i+N48];
-- 
2.25.1