From 5f17c0f6a7655909fdbb879a9afcae85783dc845 Mon Sep 17 00:00:00 2001
From: Zilog80 <rs1729@users.noreply.github.com>
Date: Sat, 13 Mar 2021 08:49:09 +0100
Subject: [PATCH] iq_svcl: sum of dB -> avg dB, i.e. dB(sum FFT)

---
 demod/iq_svcl/iq_server.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/demod/iq_svcl/iq_server.c b/demod/iq_svcl/iq_server.c
index 79dba32..b78cdba 100644
--- a/demod/iq_svcl/iq_server.c
+++ b/demod/iq_svcl/iq_server.c
@@ -290,8 +290,8 @@ static void *thd_FFT(void *targs) {
     int bitQ = 0;
 
     float complex *z = NULL;
-    float *db     = NULL;
-    float *sum_db = NULL;
+    float *avg_rZ = NULL;
+    float *avg_db = NULL;
 
     dsp_t dsp = {0};  //memset(&dsp, 0, sizeof(dsp));
 
@@ -326,8 +326,8 @@ static void *thd_FFT(void *targs) {
 
     z = calloc(dsp.decM+1, sizeof(float complex));  if (z  == NULL) goto exit_thread;
 
-    db     = calloc(dsp.DFT.N+1, sizeof(float));  if (db     == NULL) goto exit_thread;
-    sum_db = calloc(dsp.DFT.N+1, sizeof(float));  if (sum_db == NULL) goto exit_thread;
+    avg_rZ = calloc(dsp.DFT.N+1, sizeof(float));  if (avg_rZ == NULL) goto exit_thread;
+    avg_db = calloc(dsp.DFT.N+1, sizeof(float));  if (avg_db == NULL) goto exit_thread;
 
 
     int j, n = 0;
@@ -378,15 +378,16 @@ static void *thd_FFT(void *targs) {
 
                     raw_dft(&(dsp.DFT), dsp.DFT.Z);
 
-                    db_power(&(dsp.DFT), dsp.DFT.Z, db);
-                    for (j = 0; j < dsp.DFT.N; j++) sum_db[j] += db[j];
+                    for (j = 0; j < dsp.DFT.N; j++) avg_rZ[j] += cabs(dsp.DFT.Z[j]);
 
                     sum_n++;
                     n_fft = 0;
                 }
                 if (sum_n*fft_step*mlen >= sec*dsp.sr_base) {
 
-                    for (j = 0; j < dsp.DFT.N; j++) sum_db[j] /= (float)sum_n;
+                    for (j = 0; j < dsp.DFT.N; j++) avg_rZ[j] /= dsp.DFT.N*(float)sum_n;
+                    for (j = 0; j < dsp.DFT.N; j++) avg_db[j] = 20.0*log10(avg_rZ[j]+1e-20);
+
 
                     pthread_mutex_lock( (dsp.thd)->mutex );
                     fprintf(FPOUT, "<%d: FFT>\n", (dsp.thd)->tn);
@@ -401,7 +402,7 @@ static void *thd_FFT(void *targs) {
                         l = write(tharg->fd, sendln, sendln_len);
                         for (j = dsp.DFT.N/2; j < dsp.DFT.N/2 + dsp.DFT.N; j++) {
                             memset(sendln, 0, LINELEN+1);
-                            snprintf(sendln, LINELEN, "%+11.8f;%7.2f\n", bin2fq(&(dsp.DFT), j % dsp.DFT.N), sum_db[j % dsp.DFT.N]);
+                            snprintf(sendln, LINELEN, "%+11.8f;%7.2f\n", bin2fq(&(dsp.DFT), j % dsp.DFT.N), avg_db[j % dsp.DFT.N]);
                             sendln_len = strlen(sendln);
                             l = write(tharg->fd, sendln, sendln_len);
                         }
@@ -413,7 +414,7 @@ static void *thd_FFT(void *targs) {
                         if (fpo != NULL) {
                             fprintf(fpo, "# <freq/sr>;<dB>  ##  sr:%d , N:%d\n", dsp.DFT.sr, dsp.DFT.N);
                             for (j = dsp.DFT.N/2; j < dsp.DFT.N/2 + dsp.DFT.N; j++) {
-                                fprintf(fpo, "%+11.8f;%7.2f\n", bin2fq(&(dsp.DFT), j % dsp.DFT.N), sum_db[j % dsp.DFT.N]);
+                                fprintf(fpo, "%+11.8f;%7.2f\n", bin2fq(&(dsp.DFT), j % dsp.DFT.N), avg_db[j % dsp.DFT.N]);
                             }
                             fclose(fpo);
                         }
@@ -464,8 +465,8 @@ static void *thd_FFT(void *targs) {
   exit_thread:
 
     if (z) { free(z); z = NULL; }
-    if (db) { free(db); db = NULL; }
-    if (sum_db) { free(sum_db); sum_db = NULL; }
+    if (avg_rZ) { free(avg_rZ); avg_rZ = NULL; }
+    if (avg_db) { free(avg_db); avg_db = NULL; }
 
     reset_blockread(&dsp);
     (dsp.thd)->used = 0;