7
higher impedance setting, while active pickups probably a
lower. Passive pickups generally will have more sensitivity to
input impedance, but there are no hard and fast rules. Check
with the manufacturer of your particular pickup system to see
if they recommend a specific input impedance for their device.
Ultimately, as is with so many things like this, the final judge
of this setting should be your ears. Impedance mismatches at
this stage may not even be audible, or very subtle, or totally
apparent. But trust yourself here – nothing will break if you
have the wrong setting – just audition the 3 positions of the
impedance switch and if one sounds better over the other 2,
then that’s the correct setting.
Phase Reverse
ALiX has a phase reverse switch, located on the rear panel, top
right (facing the rearpanel), directly above the input impedance
switch. Use this to toggle the polarity of audio signal.
Phase relationships can be very complicated, and discrepancies
can result in highly accentuated or de-accentuated bass
response of an out of phase signal. Or it can sound hollowed
out and thin, or just downright weird. Again, the rule of thumb
here is whatever sounds right is probably right.
There may be setup scenarios where the front of house or
monitor engineer requires you to try flipping the phase to
achieve better phase coherency with other signals in the mix.
At the very least, it’s good for you to know how to operate this
controls and hear it in use with your instrument.
9.3 FILTERING AND EQ
One of the defining features of our ALiX is the very powerful,
EQ / filter controls. If you haven’t used EQ’s or filters much,
we will provide a basic overview here. But the full science of
this process is more than we can cover here, so we strongly
recommend some adjunct reading:
http://en.wikipedia.org/wiki/Equalization
As with all audio processing techniques, the more you know,
the better you will sound.
HPF / Notch
This is the upper control to the right of the GAIN knob. To
select between HPF and Notch, adjust the left side DIP switch
locations # 1.
HPF: A High Pass Filter will only allow signal information above
its set frequency to pass downstream to the output. This
filter employs 12dB per octave roll off and uses a Thomson –
Butterworth response for the best combination of passband
flatness and time domain response. Yes, that will be on the quiz.
GAIN
Hz
40
125
20k
1k
0dB
-12dB
HIGH PASS FILTER
Simply put, use the high pass filter to cut unwanted bass
frequencies out of a signal. Usually a HPF is used to eliminate
rumble or non-musical low frequency information out of a
signal. But this HPF range is from 20Hz to 1.0kHz, so you can
make very dramatic filter settings.
Some instruments won’t have any information below a
certain frequency. Fiddle for example only extends its lowest
fundamental down to 200Hz. So if you are amplifying a fiddle,
you could safely set the HPF at 150 – 200 Hz without hearing
much effect in the tonality of the instrument. Whereas a bass
can have a low fundamental down around 30Hz, so setting the
HPF any higher than that could affect its tonality.
If you are on a stage with an acoustic guitar, and there is lots of
low end making you sound bad, or feeding back or both, the
HPF might be your first stop to try to control those problems.
Notch: A notch filter is a very sharp and deep cut of a specific
frequency. This is used predominantly to find and remove a
specific problem frequency that may be feeding back through
stage monitors or amps, or to simply cut out a very specific,
narrow unwanted part of an instrument’s frequency range. This
notch uses the same frequency sweep range of 20Hz – 1.0kHz.
GAIN
Hz
40
125
20k
1k
0dB
-12dB
NOTCH FILTER
Parametric Mid Controls
The mid range section of ALiX’s equalizer is fully parametric,
which enables you control the mid range gain, frequency and Q
independently. The range of these controls are:
Gain
= +/- 12dB,
Freq range LO setting
= 70Hz – 880Hz
Freq range HI setting
= 670Hz – 8.0kHz
Q
= .5 – 5
The frequency range can be switched between the LO and
HI settings via the left side panel DIP switch locations # 2.
With these two available ranges, the over all range of the mid
controls is very wide, which enables targeting of specific sonic
areas of a multitude of instrument or pickup types.
GAIN
Hz
20
1k
20k
MID EQ
0dB
-12dB
+12dB
Q
Q factor determines the sharpness of the bandwidth of the
frequency being adjusted. A higher Q factor setting – turning
the Q knob further clockwise - creates a sharper bandwidth
and thus a more targeted, surgical EQ adjustment. Alternately,
a lower Q factor - turning the Q knob further counter clockwise
- creates a broader tonal adjustment.
Low Control
