SQN-4S IVe User's Handbook
recorder will not be overloaded by a limited transient output from the mixer. Most of the ENG
recorders use VU meters, with which the Peak Level is off scale. The reference point we use,
therefore, is the Nominal Line Level - the level to which the mixer’s Line-Up tone is set. Experience
has shown that most of the usual ENG recorders are calibrated so that their Nominal Line Level or
0VU is only 6dB below the level at which distortion is beginning to increase. Accordingly, it has
become the practice to adjust the recorder’s gain control to place the mixer’s Line-Up tone at -2dB on
the recorder’s VU meter. Some recordists prefer to go further and leave themselves a little more
headroom on the recorder by placing the line up tone at -4dB on the recorder’s meter.
Interfacing to a digital recorder with its much more sudden and unforgiving overload characteristic
requires that the Nominal Peak Level of the mixer be placed below the peak level of the recorder.
This is because the limiting, as carried out on the mixer assumes that the following recorder is
tolerant of some degree of overload for periods up to 1ms, hence the emphasis on the measurement
using a Peak Programme Meter in the paragraph above. Fortunately, digital recorders, because of
their clipping characteristics, are almost always fitted with fast peak meters, reading on a sample by
sample basis. It is easy to set the matching between the mixer and the recorder experimentally using
limited transients such as sharp handclaps. Typically, the Line-Up tone should be placed 12dB below
the allowed peak level.
6. AUXILIARY MONITOR INPUTS The SQN-4S Series IV features twin auxiliary inputs on its 12-
way [MAIN] connector [A] which are intended to accept a return signal from whatever recorder the
mixer is feeding. The input sensitivity is set by adjusting the screwdriver-operated potentiometer
marked [MONITOR SENSITIVITY ADJUST] in the base of the mixer and can usually be fixed with
sufficient accuracy by ear by operating the [MIXER AUX] switch situated below the Master fader to
and fro with the line-up tone on and adjusting for parity of loudness. This feature allows before/after
comparison of off-tape monitoring, or, when used with a recorder that lacks off tape monitoring, it
can be used as a check that mixer outputs are at least reaching the recording inputs. The [MIXER
AUX] switch affects only the headphone signals.
Many ENG recorders feature an ‘Earphone Monitor’ output on a 3.5mm jack, intended for the
cameraman’s use. This often carries audio warning of tape end or other errors, but because it is fed
from the recording head the practice has grown of using it for audio confidence monitoring even
though it is usually Dolby encoded, contaminated by time-code noise, unbalanced and at very low
level (typically -16dBu). Cable looms incorporating quad stereo leads in a single flexible cable of
only 7mm diameter have been developed at SQN for use in interfacing such recorders with the 12-
way [MAIN] socket [A] of the mixer. They are available in straight or coiled formats.
7. MICROPHONES The four identical XLR-3F microphone input connectors are wired to conform
with the IEC standard (Pin 1 ground, Pin 2 in phase and positive for T-powering). The SQN-4S is
designed to accommodate all professional microphones and assumes a source impedance for dynamic
microphones in the range 150-600 Ohms. Condenser microphones, of course, will present source
impedances much lower than this but because of the absence of input transformers in the mixer, the
frequency response will be unaffected. It is outside the scope of this manual to describe in any detail
the various types of microphone which may be employed, but the type will determine the settings of
switches set into the baseplate of the mixer. While the SQN-4S has sufficient current capacity to
supply any make of condenser microphone, the use of microphones which have a particularly large
current drain with battery-powered equipment will need careful consideration. Some marked
improvement in performance or special tonal characteristic should be required as compensation for
the reduced battery life. There are some powered microphones that are switchable or automatically
switch between 48V and 12V phantom powering. These will typically have their power consumption
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