GEAR 23_COVER - JHS

allowing the high frequencies to ‘pass
through’. It’s particularly useful in live
situations to reduce stage rumble or
microphone ‘popping’, which can produce a
muddy mix, or to clean up male vocals and
filter out low frequency hum. The A & H HPF
is a 2-pole filter rolling off at 100Hz; 2-pole
means it will roll off at 12dB per octave.
EQ Section
The equaliser section allows you to change
the tone of the sound on each input. Do not
confuse this section with, say, your guitar
amp’s EQ – these are designed to only enhance
the frequency range of a guitar. The A & H EQ
covers the whole of the audio range.
An EQ section is normally split into ‘bands’
which control a range of frequencies, in a
similar fashion to the treble and bass tone
controls on your home hi-fi.
The ZED has 3-band EQ, with a separate
control for the middle audio frequencies.
This control is also ‘swept’ which provides
even more sophistication. Simply described,
a sweep EQ allows you to choose the exact
frequency to cut and boost, rather than
having it chosen for you,
as on normal “fixed”
controls.
• HF EQ gives
+/-15dB boost or cut,
with a corner frequency of 12kHz.
• MF EQ gives +/-15dB boost of cut,
which has a variable frequency range
from 120Hz to 4kHz.
• LF EQ gives +/-15dB cut or boost with
a corner frequency of 80Hz.
Auxiliary Section
Auxes 1 & 2
Each of these controls sends a signal to an
auxiliary bus. The signal is sourced pre-fade
which means that the level is independent of,
and unaffected by the fader. Auxes 1 & 2 are
primarily used for foldback monitoring
purposes, as the fader does not affect the
level. They can also be used as feeds for
recording and are available sources to the
USB interface for this purpose. These sends
are affected by the Mute switch, so muting
the channel will also mute the Aux sends.
Input Path. The control varies the signal level
to the bus from off (fully attenuated) to
+6dB, with unity gain at the arrow.
There are master level controls for the Aux 1
& 2 outputs situated in the master section of
the mixer.
Auxes 3 & FX
These are post-fade sends, which means that
the signals are affected by the channel fader.
Primarily used for effects sends, the aux
signal will reduce if the fader is pulled down,
so keeping the correct proportion of the
effect. Muting the channel will also mute the
Aux sends, and the send controls have 6dB
gain fully clockwise. There are no master level
controls for Aux 3 & 4 outputs.
Let me explain pre- and post- fader. The
signal applied to the auxiliary or effects
mixing bus(ses) may be derived before (pre)
or after (post) the channel's fader. This pre or
post fader signal still must go through the
auxiliary or effects send level control before
it is applied to the aug or efx bus. When an
auxiliary or effects mix is derived pre fader,
fader adjustments made to alter the primary
mix will not affect that auxiliary mix. Only
the send level control adjusts this mix. Post
fader auxiliary or effects sends are still
subject to the send level control, but they
also track fader changes.
Post fader sends are often used for feeding
echo or reverb devices because one generally
wants the echo sound to fade out when
the channel is faded out of the
mix. Sometimes, for special
effects, one may prefer a
pre fader echo send;
when the
channel is
faded, its echo
component
lingers until the echo
send control is turned down,
giving the appearance of a sound
moving off ‘into the distance’.
Auxiliary mixes for stage monitoring or
sub-mixes for remote use are generally
derived pre fader. In this way, channel
fader adjustments that are intended to fine
tune the main house mix will not distract
performers on stage or cause inappropriate
imbalances in broadcast or recording feeds.
It is important to remember that performers
on stage use their monitor mixes to judge
their own playing or vocal dynamics, and the
balance between band members. If these
balances are arbitrarily changed during a
performance because the mixing engineer
is attempting to alter the house mix and
the monitor feeds happen to be derived
post fader, the entire performance will be
adversely affected.
On the other hand, there may be exceptions,
particularly in small clubs where the stage
monitor speakers spill into the audience to
a large extent, where compromises must be
accepted, and the stage monitor mix is best
done post fader.
PAN (Panoramic Control)
The pan control adjusts how the signal from
the mono input channel is shared between
the left and right buses and subsequently the
main stereo outputs. Set to the mid position,
equal amounts of signal are fed to left and
right, with pan set to L, none is sent to the
Right bus.
A pan pot is nothing more than a pair of
specially tapered pots (level controls) wired
back-to-back so that as the level going out of
one pot increases, the level going out of the
other decreases. In sound system applications,
it is desirable to taper the resistance elements
in the two sections of the pan pot so that
when the pot is centred, the output level
from each section is 3 dB less than it would
be if the pot were turned all the way up for
the individual section (all the way to one side).
The total POWER then coming out of the
loudspeaker system will be the same with
the pot centred as with the pot to one side
or the other (two amplifiers each producing
3 dB less than full power equal the same as
one amplifier producing full power).
PFL & PK! LED
The PFL (Pre-Fade Listen) switch sends the
channel signal to the PFL bus and subsequently
to the headphones and the main L R meters.
Used for checking the audio signal before
raising the fader or un-muting the channel.
The PK! LED illuminates dimly to indicate the
PFL switch is pressed, and brightly to indicate
the channel signal is within 5dB of clipping.
Fader
This determines the level of the input signal
within the mix and provides a visible
indication of channel level. All A&H desks
come with 100mm travel faders which provide
greater control snd smoother response than
the limited 60mm travel faders often fitted to
budget concious mixers.
Mute Switch
This mutes or cuts the signal to the left and
right buses and the Aux buses. A rectangular
LED illuminates to show the Mute switch is
pressed.
NEXT ISSUE
Okay, Kevin’s talked you down through a
channel strip on the excellent Allen & Heath
ZED22FX. In the next Gear, he looks at stereo
operation, how to introduce the onboard desk
effects into your mix, and the all-important
output control section on your desk.
ALLEN&HEATH
www.allen-heath.co.uk
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