From: Luca Trisciani <luca.trisciani@dcp-werkstatt.ch>
Date: Fri, 22 Mar 2019 10:30:57 +0000 (+0100)
Subject: Comment on the calculation of final offset
X-Git-Tag: v0.0.1~72
X-Git-Url: https://git.carlh.net/gitweb/?p=leqm-nrt.git;a=commitdiff_plain

Comment on the calculation of final offset
---

diff --git a/src/leqm-nrt.c b/src/leqm-nrt.c
index efc89a1..d36e0e0 100644
--- a/src/leqm-nrt.c
+++ b/src/leqm-nrt.c
@@ -910,11 +910,18 @@ int sumsamples(struct Sum * ts, double * inputsamples, double * cinputsamples, i
 int meanoverduration(struct Sum * oldsum) {
   oldsum->mean = pow(oldsum->sum / ((double) oldsum->nsamples), 0.500);
    oldsum->cmean = pow(oldsum->csum / ((double) oldsum->nsamples), 0.500);
-   oldsum->rms = 20*log10(oldsum->mean) + 108.0851;
-   oldsum->leqm = 20*log10(oldsum->cmean) +  108.0851;//  
-     //This must be right because M filter is -5.6 @ 1k Hz that is -25.6 dBFS and to have 85.0 as reference level we must add 25.56 + 85.00 that is 110.6 dB.
-   //this value is obtained calibrating with a -20 dBFS. 
-
+   oldsum->rms = 20*log10(oldsum->mean) + 108.010299957;
+   oldsum->leqm = 20*log10(oldsum->cmean) +  108.010299957;//
+
+     /*
+How the final offset is calculated without reference to a test tone:
+P0 is the SPL reference 20 uPa
+Reference SPL is RMS ! So 85 SPL over 20 uPa is 10^4.25 x 0.000020 = 0.355655882 Pa (RMS), 
+but Peak value is 0.355655882 x sqr(2) = 0.502973372 that is 20 x log ( 0.502973372 / 0.000020) = 88.010299957
+To that one has to add the 20 dB offset of the reference -20dBFS: 88.010299957 + 20.00 = 108.010299957 
+   */
+   /*But ISO 21727:2004(E) ask for a reference level "measured using an average responding meter". So reference level is not 0.707, but 0.637 = 2/pi
+   */
 return 0;
 }
 
@@ -937,7 +944,7 @@ void logleqm(FILE * filehandle, double featuretimesec, struct Sum * oldsum) {
 }
 
 void logleqm10(FILE * filehandle, double featuretimesec, double longaverage) {
-  double leqm10 = 20*log10(pow(longaverage, 0.500)) +  108.0851;
+  double leqm10 = 20*log10(pow(longaverage, 0.500)) +  108.010299957;
   fprintf(filehandle, "%.4f", featuretimesec);
   fprintf(filehandle, "\t");
   fprintf(filehandle, "%.4f\n", leqm10);