Apex Digital dBQ-zero, User Manual

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14
Using the dBQ-zero
Operation of the dBQ-zero is straightforward. However, if you
would like to know the finer details of this equaliser, then we
invite you to read on.
Graphic EQ section
The graphic EQ section consists of 30 faders adjusting the gain
of 30 band-pass filters, each spaced by a 1/3rd of an octave.
These filters have a fixed centre frequency, as defined by the
ISO standard, and a fixed Q-factor.
The Q-factor of a filter is defined as the ratio of its centre
frequency to its bandwidth: Q = f / Bw. The greater the Q, the
smaller the bandwidth. The bandwidth is measured between
the ±3 dB points on either side of the band-pass centre
frequency. With Constant-Q designs, such as that found in the
dBQ-zero, the bandwidth of each of the band-pass filters stays
constant no matter what the boost or cut of the filter is. The use
of Constant-Q filters ensures that the composite filter response
of the graphic EQ accurately follows the physical positions of
the front panel faders. This is achieved by the filters minimising
frequency band interaction.
To obtain good results quickly, and to keep the program material
as clean as possible, we advise you to start from the lower
frequencies and work your way up to the higher frequencies
(from left to right). All sounds consist of a fundamental
frequency and harmonics (depending on the nature and origin
of that sound). When working from low frequencies to high you
should aim to change the fundamental first and then its higher
harmonics.
Other advice is that it is better to cut than boost. When boosting,
you will reduce the overall headroom of the system. If, for
example, there is a lack of high frequency content, you can
boost those frequencies, but it would be better to cut some of
the lower frequencies instead.
Also, try to avoid extreme differences in gain between adjacent
bands as this will create large phase shifts. Try to make your
equalisation curve as smooth as possible.
Using the Scale switch enables the fader gain range to be
changed. In its normal position (LED off) the scale is ±6 dB: this
scale is suitable for minor adjustments but with great precision.
When the Scale switch is in, the LED will light and you will have
access to a range of ±15 dB.
Adjusting the overall gain
If you have applied gain to multiple frequencies, the signal
level may become very high and hence may clip, or cause the
Using the dBQ-zero
next item of equipment to clip. Use the input level to adjust the
overall dBQ-zero gain to keep the signal in an optimal range.
Similarly, if multiple frequency bands have been cut use this
input gain to amplify the overall level back to normal.
High-pass filter
By using the high-pass filter you can remove unwanted low
frequency content/noise, such as hum, rumble or microphone
handling noise. This filter has a fixed slope of 12 dB/octave
and a cut-off frequency which is adjustable between 20 Hz and
250 Hz.
The high-pass filter may be switched on or off using the switch
adjacent to the HPF frequency control. The LED indicator lights
when the filter is enabled.
Low and high shelving filters
The low and high shelving filters are used to add or remove
excess ‘warmth’ or ‘brightness’ respectively. The frequency
of both filters is fixed. The low shelving filter has a corner
frequency of 100 Hz and the high shelving filter is fixed at 14
kHz.
Using the rotary controls enables you to adjust the level of cut
or boost applied to each filter (between ±9 dB).
Notch filters
The dBQ-zero offers two notch filters per channel, with
independent frequency selection and on/off switch. When a
notch filter is switched on, the corresponding LED will light.
The first notch filter is adjustable between 25 Hz and 1.5 kHz
and the second is adjustable between 700 Hz and 18 kHz.
The principle function of the two notch filters is to attenuate
any problem frequencies that may be causing feedback or
any other unwanted noise. Feedback is most likely to occur at
frequencies between the fixed filter bands on the graphical EQ.
This is why the notch filters are useful. Furthermore, the notch
filters have a higher degree of attenuation than the graphic EQ
filters and are therefore more efficient at preventing feedback.
Only the centre frequency of the notch filters may be adjusted by
the user. The Q-factor and attenuation have been intentionally
fixed for ease of use. The attenuation is 20 dB and the Q-factor
is 4. These settings are sufficient to remove major sources of
feedback without altering too much of the program spectrum.
Similarly to the graphical section, when trying to remove
unwanted frequencies start with the notch filter frequency