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MICROPHONE PREAMPLIFIER
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Instruction Manual
6. TYPICAL OPERATION
6.4 USING THE MICROPHONE OUTPUT LIMITER
Microphone limiters traditionally consist of a mic preamp followed by a limiter circuit.
Until MicLim was devised, that was the only practical way to do it. Everybody is familiar
with the clipped overload that’s heard when a performer suddenly gets on the mic too
loudly. The compressor/limiter held down the P. A. level, but the preamp was clipping
horribly. Until MicLim, there was no other choice except to constantly keep a hand on the
preamp’s gain knob.
The difference with MicLim
is that the limiter works with the microphone itself, before
the preamplifier has any chance to clip at all. Patent pending technology had to be devised
to make that possible since just about anything inserted between the mic and preamp
will add noise or distortion. With MicLim now available you will seldom find it possible
to overload the Model 1788A mic preamp, even under severe conditions. That’s because
there is typically 20dB of limiting headroom. Effectively that means you get 20dB more
preamp headroom before distortion.
6.5 USING POLARITY REVERSE
There will be times when you need to reverse the polarity (phase) of a mic signal. Vocalists
monitoring themselves on headphones will hear a different sound when the phase is
reversed. The reversed phase may sound fuller and more truthful or hollow and far away.
That is because there is a cancellation of frequencies within the ear when the external
sound from the headphone mixes with the sound directly conducted to the ear. “Flipping
the phase” can make the problem either more or less noticeable.
Another time when phase reversing can be helpful is in mixing multiple microphones that
are within each other’s coverage areas. The “crosstalk” between mics may come through
different delays due to the differing distances from the sound. These sounds may tend
to cancel out in the mix. You may get a “nasal” or hollow effect when all mics are on.
Pre
Amp
Peak
Limiter
Still
Heavily
Clipped
Conventional Mic Limiter
Pre
Amp
Optically
Coupled
Attenuator
Peak
Detector
No
Clipping
Aphex MicLim Mic Limiter
Distance
to Mic2
Distance
to Mic1
Sound
Cancelled
=
