Phase Reverse
The phase reverse switch is used to invert the phase of the input signal. It is active on
both mic and line inputs. This function could be required when processing a signal
that is out of phase with other signals in a mix, in which case the resultant phase error
typically appears as a loss of low frequency content, due to cancellation of out of phase
components. Phase reverse is commonly used when recording the bottom of a snare
drum (if also using a mic on top of the snare), the back of a guitar cab (if also
recording signal from the front of the cab), and when performing the stereo recording
technique known as an MS pair.
High Pass Filter
This low cut filter provides 12dB per octave of gain reduction with the -3dB point
being at 90Hz. Like the phase reverse switch, the high pass filter is active on both mic
and line inputs, and is ideal for removing low frequency rumble. The filter can be
useful in restricting 'popping' on vocals or even low frequencies caused by contact
with microphone stands or microphone cables. Popping is an undesirable thump that is
caused by close-miking certain spoken or sung letters, namely 'P' or 'B'. These
particular letters cause a sudden expulsion of air that can result in an audible thump.
As this thump has a lot of low frequency content the high pass filter can help to reduce
the problem, as can using a pop filter (a device usually made out of nylon material
similar to stockings) suspended in front of the microphone. The low cut filter is easily
bypassed for quick A/B comparison.
30dB Pad
Occasionally when using sensitive condenser microphones the source signal may be
too loud for the input preamp. In this situation, to avoid any overloading or distortion
of the mic preamp stage, the 30dB pad can be used to reduce the input gain to a more
manageable level. The 30dB pad only applies to the microphone input.
Equalisation
Before switching the EQ into circuit, it is advisable to set the cut/boost controls to
their centre, or flat, position. The EQ is brought into circuit with the 'EQ' push switch,
signalled by a green LED. Each channel has three bands of equalisation: shelving low
frequency (LF) (i.e. it extends from the selected frequency to the extreme low
frequency limit of the equaliser's response.), peaking sweepable mid (i.e. it boosts or
cuts a section of the audio spectrum around its selected centre frequency only) and
shelving high frequency (HF). The LF shelf operates at a frequency of 80Hz, while the
HF shelf is set at 12kHz. The EQ slopes have a second order 12dB/octave response,
and an associated gain control on both bands provides up to 15dB of cut or boost on
each selected frequency, controlling the full range of frequencies below the LF comer
frequency and above the HF comer frequency. The mid band has a fixed Q of 0.7
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