TL Audio M4 - Manual (Page 9)

8
Phase Reverse
The phase reverse switch, located to the bottom left of the gain control and
labeled 'PHASE', 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 four 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