From 6f75014dc5ab366da29040ef913729e980885eb3 Mon Sep 17 00:00:00 2001
From: drowe67 <drowe67@01035d8c-6547-0410-b346-abe4f91aad63>
Date: Wed, 10 Nov 2010 06:04:19 +0000
Subject: [PATCH] added #ifdef-ed code for synthsis with cos() instead of
 inverse FFT.  Works better when frame length extended to 20ms, but phase0
 model seems to break with 20ms frames.  Sticking with IFFT synthesis for now

git-svn-id: https://svn.code.sf.net/p/freetel/code@214 01035d8c-6547-0410-b346-abe4f91aad63
---
 codec2/src/sine.c | 55 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 48 insertions(+), 7 deletions(-)

diff --git a/codec2/src/sine.c b/codec2/src/sine.c
index 89cdc044..011ca0f3 100644
--- a/codec2/src/sine.c
+++ b/codec2/src/sine.c
@@ -461,6 +461,7 @@ void make_synthesis_window(float Pn[])
     Pn[i] = win;
   for(i=3*N/2+TW; i<2*N; i++)
     Pn[i] = 0.0;
+
 }
 
 /*---------------------------------------------------------------------------*\
@@ -470,16 +471,16 @@ void make_synthesis_window(float Pn[])
   DATE CREATED: 20/2/95		       
 									      
   Synthesise a speech signal in the frequency domain from the
-  sinusodal model parameters.  Uses overlap-add a triangular window to
-  smoothly interpolate betwen frames.
+  sinusodal model parameters.  Uses overlap-add with a trapezoidal
+  window to smoothly interpolate betwen frames.
 									      
 \*---------------------------------------------------------------------------*/
 
 void synthesise(
-  float  Sn_[],		/* time domain synthesised signal         */
-  MODEL *model,		/* ptr to model parameters for this frame */
-  float  Pn[],		/* time domain Parzen window              */
-  int    shift          /* used to handle transition frames       */
+  float  Sn_[],		/* time domain synthesised signal              */
+  MODEL *model,		/* ptr to model parameters for this frame      */
+  float  Pn[],		/* time domain Parzen window                   */
+  int    shift          /* flag used to handle transition frames       */
 )
 {
     int   i,l,j,b;	/* loop variables */
@@ -499,8 +500,23 @@ void synthesise(
 	Sw_[i].imag = 0.0;
     }
 
+    /*
+      Nov 2010 - found that synthesis using time domain cos() functions
+      gives better results for synthesis frames greater than 10ms.  Inverse
+      FFT synthesis using a 512 pt FFT works well for 10ms window.  I think
+      (but am not sure) that the problem is realted to the quantisation of
+      the harmonic frequencies to the FFT bin size, e.g. there is a 
+      8000/512 Hz step between FFT bins.  For some reason this makes
+      the speech from longer frame > 10ms sound poor.  The effect can also
+      be seen when synthesising test signals like single sine waves, some
+      sort of amplitude modulation at the frame rate.
+
+      Another possibility is using a larger FFT size (1024 or 2048).
+    */
+
+#define FFT_SYNTHESIS
+#ifdef FFT_SYNTHESIS
     /* Now set up frequency domain synthesised speech */
-
     for(l=1; l<=model->L; l++) {
 	b = floor(l*model->Wo*FFT_DEC/TWO_PI + 0.5);
 	Sw_[b].real = model->A[l]*cos(model->phi[l]);
@@ -509,9 +525,34 @@ void synthesise(
 	Sw_[FFT_DEC-b].imag = -Sw_[b].imag;
     }
 
+    /* zero out anything above 3500 Hz */
+
+    for(i=(3500.0/4000.0)*FFT_DEC/2; i<FFT_DEC/2; i++) {
+	Sw_[i].real = 0.0;
+	Sw_[i].imag = 0.0;
+	Sw_[FFT_DEC-i].real = 0.0;
+	Sw_[FFT_DEC-i].imag = 0.0;
+    }
+
     /* Perform inverse DFT */
 
     four1(&Sw_[-1].imag,FFT_DEC,1);
+#else
+    /*
+       Direct time domain synthesis using the cos() function.  Works
+       well at 10ms and 20ms frames rates.  Note synthesis window is
+       still used to handle overlap-add between adjacent frames.  This
+       could be simplified as we don't need to synthesise where Pn[]
+       is zero.
+    */
+    for(l=1; l<=model->L; l++) {
+	for(i=0,j=-N+1; i<N-1; i++,j++) {
+	    Sw_[FFT_DEC-N+1+i].real += 2.0*model->A[l]*cos(j*model->Wo*l + model->phi[l]);
+	}
+ 	for(i=N-1,j=0; i<2*N; i++,j++)
+	    Sw_[j].real += 2.0*model->A[l]*cos(j*model->Wo*l + model->phi[l]);
+    }	
+#endif
 
     /* Overlap add to previous samples */
 
-- 
2.25.1