All filters in the Parametric EQ section
are implemented as minimum phase
filters.
In order to ensure phase matching of
the two loudspeakers and therefore to
maintain phantom imaging
characteristics, identical Parametric
Equaliser parameters are applied to
both loudspeakers simultaneously.
Magnitude Response Plots
Low-Shelving Filter
The Parametric Equaliser has one
low-shelving filter available with a
frequency range of 32.0 Hz to 500.0 Hz
and a Q range of 0.4 to 1. The gain
ranges from -6.0 dB to +6.0 dB in
steps of 0.5 dB.
Figure 5.42: Magnitude Responses, low-
shelving filter: Fc = 100 Hz, Gain varied
from -6.0 to +6.0 dB, Q = 0.7.
Figure 5.43: Magnitude Responses, low-
shelving filter: Fc varied from 32 Hz to
500 Hz., Gain =
±
6 dB, Q = 0.7.
10
100
1,000
10,000
Frequency (Hz)
-6
-4
-2
0
2
4
6
Gain (dB)
Figure 5.44: Magnitude Responses, low-
shelving filter: Fc = 100 Hz, Gain =
±
6
dB, Q varied from 0.4 to 1. Note that, for
Q values greater than 0.7, there is an
overshoot in the magnitude response.
For a monotonically increasing (or de-
creasing) response, the Q should not be
set to a value greater than 0.7.
Peaking Filters
The Parametric Equaliser has eight
reciprocal peak-dip or peaking filters
available. All peaking filters have a Q
value that ranges from 0.5 to 8.0
where the Q is based on a bandwidth
defined by the half-gain points
. The
gain ranges from -6.0 dB to +6.0 dB in
steps of 0.5 dB. The peaking filters
have a range of 5 octaves with
differing limits as follows:
•
Four low-frequency filters with a
range of 25.0 Hz to 400.0 Hz.
•
Three mid-frequency filters with
a range of 250.0 Hz to 4.0 kHz.
•
One high-frequency filter with a
range of 2.5 kHz to 40.0 kHz.
Figure 5.45:
Magnitude Responses,
Peaking filter: Fc = 100 Hz, Gain varied
from -6.0 to +6.0 dB, Q = 1.
Figure 5.46:
Magnitude Responses,
Peaking filters: Examples of Fc varied
from 25 Hz to 25 kHz on one-octave cen-
tres, Gain =
±
6 dB, Q = 1.
10
100
1,000
10,000
Frequency (Hz)
-6
-4
-2
0
2
4
6
Gain (dB)
Figure 5.47:
Magnitude Responses,
Peaking filters: Fc = 100 Hz, Gain =
±
6
dB, Q varied from 0.3 to 8.
High-shelving Filter
The Parametric Equaliser has one
high-shelving filter available with a
frequency range of 1.0 kHz to 16.0 kHz
and a Q range of 0.4 to 1. The gain
ranges from -6.0 dB to +6.0 dB in
steps of 0.5 dB.
Figure 5.48:
Magnitude Responses,
high-shelving filter: Fc = 10 kHz, Gain
varied from -6.0 to +6.0 dB, Q = 0.7.
Note that this filter is applied to both
loudspeakers simultaneously.
4
For more information on this, please see “The Equivalence of Various Methods of Computing Biquad Coefficients for Audio Parametric Equalizers” Robert Bristow-Johnson,
Preprint 3906, 97th International Convention of the Audio Engineering Society, November 1994
25
