Aphex Channel Instruction Manual download pdf (Page 12)

230

instruction Manual

Aphex Systems Ltd. Model 230Page 10

230

master voice channel

Page 11Aphex Systems Ltd. Model 230

4.3 USING THE POLARITY SWITCH

There will be times when you need to reverse the

polarity (phase) of a mic signal. Vocalists monitor-

ing 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 dif-

fering 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. 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.

4.4 USING THE PAD

An input pad is nothing more than a resistive

attenuator that drops the level coming from the

microphone. Its purpose is to give you a way of

preventing overload of the preamp when incoming

signals become excessive.

In the 230, 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 for voice work. However, if you have brought

the GAIN all the way down and you still have an

excessive level then switch on the pad. You can then

readjust the gain as desired.

4.5 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

230 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 230.

4.6 Reserved

4.7 USING THE PHASE ROTATOR

The 230’s phase rotator is designed to help reduce

high assymmetric peaks that often occur with voice

waves. By reducing the amplitude of assymmetric

peaks, and making the wave more symmetrical,

the voice can ride louder through compressors and

limiters. This is accomplished by displacing the time

relationship of even harmonics to their fundamen-

tals. Thus, it is called a “Phase Rotator” or a “Phase

Scrambler”.

Although the intent of phase rotating is to sym-

metrify a voice wave, we have also discovered a

psychoacoustic effect that can take place. By using a

certain tuning of a 4th order all-pass filter, we found

that not only can voice symmetry improve, but sonic

clarity also improves. It’s like adding an extention to

the top and bottom end of the sound spectrum. We

introduced this effect with our SPR (Spectral Phase

Refractor) in previous Aphex products. Many people

Figure 4-3 LO CUT Response

-5

-10

-15

-20

-25

-30

20 100 1K 2K

Frequency, Hz

Response, dB

Figure 4-2 Phase Cancellation Effect

Distance

to Mic2

Distance

to Mic1

Sound

Cancelled

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