D14635.02—MARCH 2010 43
TANDBERG Codec C90 and Profiles using C90 Administrator guide
Contents Introduction Advanced configuratio n Password protection Ab out monitors Audio matters Appendices Contact us
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The filter types

The illustrations below show s the 5 different filter type s and frequency response var iations dependent on some of th e parameter
variations. The Q-value for low p ass, high pass, low shelf and hig h shelf filters should be set to 1/sqrt (2) in order to get maxim ally flat
responses. The Q-value ( or Q-factor) is defined as Q= f0/bw. Where f0= resonance frequency i n Hz; and bw=filter bandwith i n Hz.
z-1
a1
a2
b1
b2
b0
Section 1
z-1
a1
a2
b1
b2
b0
Section 4
z-1
z-1
a1
a2
b1
b2
b0
Section 5
z-1
z-1
a1
a2
b1
b2
b0
Section 6
z-1
z-1
a1
a2
b1
b2
b0
Section 3
z-1
z-1
a1
a2
b1
b2
b0
Section 2
z-1
z-1

IIR FILTER

8 equalizers are shared by the input and output connectors. Each
equalizer filter has 6 sections and each section has five parameters
(a1, a2, b0, b1, b2)

The equalizer IIR filter

The equalizer
The system has 8 user defined eq ualizers, each made up of 6
second order IIR sections, s ee the illustration below. Each of these
8 equalizers can be appli ed to one or more of the audio input and
output connectors on the cod ec.

The Audio Console application

We recommend using the Audio C onsole, with the build in
equalizer GUI, to modify the e qualizers. The Audio Conso le
application is found at the TANDBERG Deve loper Zone web page.
Go to: http://develop er.tandberg.com/web/guest /tools/
integrators/audio-co nsole

The equalizer filter parameters

Each section (1 … 6) of each use r defined equalizer (1 … 8) can
be modified independe ntly by setting the four parameters :
• Filter type (Peakin g, low shelf, high shelf, low pass, high pas s)
• Frequency
• Gain
• Q-value
To switch off one of the six equalizer sec tions; set the second
order section to have a flat freque ncy response. This can be done
by setting the filter type to “none” o r by setting the filter type to
“peaking” and the gain to “0” (zero ).
101 102 103 104
Frequency (Hz)
Peaking filter
Gain
Q
8
6
4
2
0
-2
-4
-6
-8
dB
101 102 103 104
Frequency (Hz)
Low shelf filter
Gain = 6 dB
Gain = 4 dB
Gain = 2 dB
Gain = -2 dB
Gain = -4 dB
Gain = -6 dB
8
6
4
2
0
-2
-4
-6
-8
dB
101 102 103 104
Frequency (Hz)
101 102 103 104
Frequency (Hz)
High shelf filter
8
6
4
2
0
-2
-4
-6
-8
dB
Gain = 6 dB
Gain = 4 dB
Gain = 2 dB
Gain = -2 dB
Gain = -4 dB
Gain = -6 dB
101 102 103 104
Frequency (Hz)
Low pass and high pass fi lters
Highpass filter
2
0
-2
-6
-8
-10
-12
-14
-16
-18
-20
Lowpass filter
dB
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Contents
Introduction
Advanced configuratio n
Password protection
About monitors
Audio matters
Appendices
Audio matters