Polycom SoundStructure C16 Design Manual page 130

To enable the graphic equalizer, select Graphic from the Output EQ Type parameter and to enable the
parametric equalizer, select Parametric from the Output EQ Type parameter, as shown in the following
figure.
Output EQ Type Parameter in SoundStructure Studio
The center frequencies of a graphic equalizer are specified in the ISO 266 standard. These are similar to
the standard set of resistor values, but the series is chosen to map well to fractional octave and decade
intervals between center frequencies. The nominal frequencies are used to label each band in the equalizer.
Depending on the fractional octave size of the equalizer, a different number of bands is needed to cover the
audio frequency range. The most common graphic equalizers (and those implemented in this algorithm) are
1-octave (10 band), 2/3-octave (15 band), and 1/3-octave (31 band).
The nominal and exact center frequencies of these equalizers are shown in the following table.
Equalizer Nominal and Center Frequencies
Center Freq (Hz) 1 octave band
20 —
25 —
32 0
40 —
50 —
63 1
Polycom, Inc.
2/3 octave band 1/3 octave band
— 0
0 1
— 2
1 3
— 4
2 5
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