Focusrite OctoPre Instructions Manual page 5

LINE (Switch)
When engaged (in), this switch selects the corresponding rear panel LINE INPUT for
the channel, and an LED is illuminated in the switch cap to indicate that the LINE
INPUT is active. If this is disengaged (out), the corresponding MIC INPUT is active.
+48V (Switch)
This provides +48V of phantom power for condenser microphones when engaged,
affecting the channel's corresponding MIC INPUT only. If you are unsure whether
your microphone requires phantom power, refer to its user guide before connecting, as
it is possible to damage some microphones (most notably ribbon microphones) by
providing them with phantom power.
(Switch)
This is a high-pass filter, which removes unwanted low frequencies such as stage
rumble via microphone stands or 'proximity effect' (where low frequencies are over-
emphasised when using certain types of microphone at close range.)
LEVEL (Knob)
This sets the signal level for the channel. Connect an input signal to the unit, ensuring
that the LEVEL control is set fully anti-clockwise, and increase the LEVEL control so
that the green SIG LED is always illuminated when there is a signal present. The red
O/L (Overload) LED may light occasionally, but only if the input signal gets
particularly loud. If the O/L LED stays on continuously for any period, or you hear
the unit distort during loud peaks, you should reduce the LEVEL.
With the MIC INPUT selected, the LEVEL control provides 0dB (fully anti-
clockwise) to +60dB (fully clockwise) of gain. With the INST input selected (channels
1 & 2 only), the LEVEL control provides +4dB to +34 dB of gain.
With the LINE INPUT selected, the gain is adjustable from –10dB to +10dB. Setting
the LEVEL control to the 12 o'clock position will not alter the gain of a line level
input signal.
DYNAMICS (Knob)
The DYNAMICS control allows compression to be applied to the signal. With the
control fully anti-clockwise, no compression is applied. As the control is turned
clockwise, the compression threshold is reduced and ratio increased, resulting in
heavier and heavier compression of the signal. The yellow COMP LED increases in
intensity as compression is applied.
A compressor acts like an automatic volume control, effectively turning down the
volume of a signal if it gets too loud. It therefore reduces variation between loud and
quiet parts of a signal, by automatically reducing the gain when the signal rises above a
certain volume (the 'threshold'). Compression tends to even out a performance,
stopping the instrument from leaping out of the mix, or disappearing into it, as well as
protecting any following processes (such as A/D conversion) from overloading.
Compression can also make things sound louder, without actually increasing the peak
level. For more information on compression, refer to the 'Beginner's Guide to
Compression' on page 8.
The Dynamics control incorporates a 'brick-wall' limiter with a fixed threshold of +20
dBu, to prevent the A/D converter from overloading (which would result in
unpleasant digital distortion). The red LIMIT LED lights when limiting is taking place.
Note that the limiter is always in circuit (unless the pot is set fully anti-clockwise) to
catch signal peaks. However, the more compression is applied (i.e. the higher the
setting of the DYNAMICS control), the less likely the limiter is to be activated.
ENGLISH
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