7.4.2 Correlator
The circuit of this is described in 12.18. It gives a positive indication on the
meter if the signals at the two inputs are in phase and a negative indication if they
are out of phase. If the two signals are completely uncorrelated the meter will
remain on its centre zero. The circuitry is such that indication is inhibited if the
signal levels in the two channels differ by more than about 20dB.
7.4.3 Low Level Meters
The Correlator requires an amplifier in each channel which will be linear at
low levels but which will limit at high signal levels. These amplifiers have been
made to meet a double purpose by adding rectifiers and meters. The meters are
the same size as the limiter/compressor meters, and are similarly mounted. They
are calibrated from –60 to –40dB these being levels with respect to a 0dBV signal at
an output. Since the normal internal signal level is –10dBV, this range corresponds
to –70 to –50dBV at the input to the correlator. These meters are useful for giving
an indication of the level of very low level signals or of excessively high noise levels.
Since the correlator inputs are taken from points in the monitor channels
subsequent to the control room monitor level control, the low level meter readings
are correct only when this control is on zero. By use of this control, the range of the
meters can be extended 20dB in either direction. Thus with a range extending to –
80 V.U. the noise of various parts of the mixer itself can be checked.
7.4.4 Meter Connections
An 11-pin socket is provided to receive the flying lead with a mating plug
which connects to the Correlator and the two low level meters on the frame. The
+20V and –20V are also available on this socket for test purposes.
7.5
Synchronous Replay
7.5.1 Input – Synchronous
Replay signals are available on the selector switches for the control room
loudspeakers and also for the studio playback. The input socket and input
transformers are located in the Studio Playback Cassette (see 8.1.1) and –10dBV
lines are brought through the main cableform to the Control Room Monitor Cassette
where the left and right signals are available at the left and right monitor selector
switches.
7.5.2 Synchronous Replay to Cue
The input lines are connected to the inputs of unity gain Amplifiers G the
outputs of which feed 5k
Ω
carbon potentiometers, which act as level controls. The
sliders of these are connected to the inputs of Amplifier B the outputs of which feed
the Cue Bus Lines, Left to Cue 1 and Right to Cue 2.
