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MMDVM
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Change emphasis time constant to 750µS

This commit is contained in:
Geoffrey Merck 2020-04-30 10:26:04 +02:00
parent b2f33fd4d2
commit 69e39e36b0
2 changed files with 14 additions and 11 deletions
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4
FM.cpp
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@ -39,8 +39,8 @@ m_hangTimer(),
m_filterStage1( 724, 1448, 724, 32768, -37895, 21352),//3rd order Cheby Filter 300 to 2700Hz, 0.2dB passband ripple, sampling rate 24kHz
m_filterStage2(32768, 0,-32768, 32768, -50339, 19052),
m_filterStage3(32768, -65536, 32768, 32768, -64075, 31460),
m_preemphasis(32768, 13967, 0, 32768, -18801, 0),//75µS 24kHz sampling rate
m_deemphasis (32768, -18801, 0, 32768, 13967, 0),//75µS 24kHz sampling rate
m_preemphasis(32768, 1771, 0, 32768, -30997, 0),//750µS 24kHz sampling rate
m_deemphasis (32768, -30997, 0, 32768, 1771, 0),//750µS 24kHz sampling rate
m_blanking(),
m_useCOS(true),
m_rfAudioBoost(1U),

21
Tools/emphasis.txt
View File

@ -9,21 +9,24 @@ clear all;
clc;
fs = 24000;
timeConstant = 0.00075; %750µS
samplingtime = 1/fs;
% analog prototype
A2 = [1];
B2 = [0.000075 1];
B2 = [timeConstant 1];
% Pre
Ds = tf(B2, A2);
%Ds = tf(B2, A2);
% De
% Ds = tf(A2, B2);
Ds = tf(A2, B2);
Ds = Ds/dcgain(Ds);
% MZT
T1 = 0.000075; % 75us
T1 = timeConstant;
z1 = -exp(-1.0/(fs*T1));
p1 = 1+z1;
@ -37,12 +40,12 @@ b2 = 0;
% swap between a1, b1 to select pre- or de-emphasis
# Pre
Bmzt = [b0 a1 b2]
Amzt = [a0 b1 a2]
% Pre
%Bmzt = [b0 a1 b2]
%Amzt = [a0 b1 a2]
% De
% Bmzt = [b0 b1 b2]
% Amzt = [a0 a1 a2]
Bmzt = [b0 b1 b2]
Amzt = [a0 a1 a2]
DzMZT = tf(Amzt, Bmzt, samplingtime);
DzMZT = DzMZT/dcgain(DzMZT);