8
a TRS output jack, you can simply use a standard TRS cable to
connect both sources to Felix 2, then EQ and blend each signal
accordingly. The sonic results of this kind of acoustic pickup
system can be very excellent.
Input Impedance Selection
Both instrument inputs have 3 different impedance settings:
CH1: med - 1MΩ / hi -10MΩ / low – 10kΩ
CH2: med - 1MΩ / hi -20MΩ / low – 332kΩ
In general, most passive pickups will want to connect to a
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,
than that’s the correct setting.
12V Power
Both CH1 and CH2 instrument inputs can be used to amplify
an electret capacitor microphone. These are common for
applications where small microphones are mounted inside
acoustic instruments, or lavalier style microphones used
somewhere on the outside of the instrument. Normally these
microphones will contain very small integrated preamps which
require a small voltage to power. So the Felix 2 can send 12V
phantom power out on both of these inputs. This is activated
via DIP switch # 5 on the side panel.
12V power can be applied to the tip, ring or neither of each
channel’s input jack. Configuration is done via internal jumpers,
described in detail on page 12.
NOTE: this power supply charges up slowly, so you may need to
wait a few seconds before signal from your electret mic is present
at the input of Felix 2. And, as with 48V phantom power in the XLR
mic input, it is always best to make your input connections before
applying power at the DIP switch, and power OFF the 12V at the
DIP switch before disconnecting your source.
Phase Reverse
Both CH1 and CH2 have phase reverse switches, located on
the left side panel, directly next to the 48V phantom power
switch. Use these to toggle the polarity of either channel.
Experiment with these methodically – one at a time, to find
the setting that sounds right. If you are blending two sources
on one instrument, you may find that flipping the polarity on
one source or the other sounds best. If you are using Felix 2 to
toggle between two different instruments, you probably won’t
need to mess with their polarity.
Phase relationships can be very complicated and discrepancies
can result in highly accentuated or de-accentuated bass
response of a blended 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
these controls and hear them in use with your instruments.
9.4 FILTERING AND EQ
One of the truly defining features of our pal Felix 2 is the
very powerful, fully independent EQ / filter controls on
each channel. Each channel has identical controls, so the
descriptions in this section apply to both CH1 and CH2.
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 next control to the right of the GAIN knob for each
channel. To select between HPF and Notch, adjust the left side
DIP switch locations # 1 & 2 respectively for channels 1 & 2.
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
