207d
instruction Manual
Aphex Systems Ltd. Model 207D
Page 12
207d
2-ch tube mic preamp with adc
Page 13
Aphex Systems Ltd. Model 207D
tend to cancel out in the mix. You may get a “nasal”
or hollow effect when all mics are on. Changing the
polarity of one or more mics will often clear up the
problem. It is always worth the time to experiment
with mic polarity.
4.3.3 USING THE PAD
An input pad is nothing more than a resistive
attenuator that drops the level coming from the
input jack. Its purpose is to give you a way of prevent-
ing overload of the preamp when incoming signals
become excessive. Another purpose is to change the
preamp’s mic input into a line input.
In the 207D, we provided a pad of 20dB. That means
when the pad is on, the net gain of the preamp is
20dB lower than normal. You will almost never need
the pad unless you are using a high level microphone
on a high level source (e.g., kick drums). If you have
brought the GAIN all the way down and you still have
an excessive output level then switch on the pad. You
can then readjust the gain as desired.
4.3.4 USING LOW CUT
In the practical world, mics pick up all sorts of
unwanted low frequencies such as hand noise, wind
rumble, or lectern thumps. We designed into the
207D a very effective way of cutting out these low
frequencies while maintaining a sense of normal low
end response. Switching on the LOW CUT FILTER rolls
off all frequencies below 70Hz at 12dB per octave
but places a slight compensation around 120Hz to
improve the low end phase distortion and perception
of remaining bass. We first offered this cutoff shape
with our Model 107 tube mic preamp and it received
tremendous acclaim from vocalists and recordists
alike. So, not wanting to waste a good thing, we car-
ried it forward to the Model 207D.
Use the LOW CUT filter whenever you need it. How-
ever, please try going without if whenever possible.
Even though it is outstanding as a rumble fixer, you
will notice its presence. We suggest, as a matter of
good practice, that you always try isolating the mic
from unwanted vibrations instead of summarily
switching in the LOW CUT filter.
4.3.5 USING MicLim™
MicLim™ works best on microphones having an
impedance of 50 ohms or higher. That includes just
about every powered and passive microphone in exis-
tence. Additionally, the use of phantom power in no
way inhibits the performance of MicLim™.
All you have to do is turn MicLim™ on and it will
instantly become armed. Nothing will happen, how-
ever, until an audio peak approaches clipping: then
the limiter will act on the microphone signal to pre-
vent the peak from reaching the clip point. Whenever
the limiter hits a peak, the yellow LIMITING light will
flash.
There are no special rules about making MicLim™
work for you. The concept is simple: run the preamp
gain at a point where the peaks indicated on the
Headroom Meter only reach the MicLim™ threshold
infrequently or unexpectedly. The great advantage of
operating in this manner is to keep the audio signal
far above the noise but fearing no distortion should
the sound level suddenly increase. Recording this way
can give you an uncanny sense of dimension because
the background will have no audible noise, even at
high monitoring levels. For those who will send this
207D’s output to a digital audio workstation, the
greatest benefit is maximizing the use of the quan-
tum dynamic range. The closer to the “top” you digi-
tize a signal, the more digital resolution you get. You
lose 1 bit of digital for every 6dB under maximum,
so keeping the signal “up to the top” guarantees the
best digital audio.
By now it may be apparent that if you deliberately
increase the preamp gain until peaks frequently drive
MicLim™ to limiting, you could obtain a very dense
output level by bringing the average signal so much
Figure 4-3 LO CUT Response
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Frequency, Hz
Response, dB
Using the 207D