b) It can modify the tape speed of the Nagra in order to render the playback pilot signal synchronous
with a pilot signal coming in on the PILOT socket. For this speed correction to take place, the Nagra
must be switched to "LOUDSPEAKER PLAYBACK" and the "PILOT" indicator should show a white
cross. The white cross is only shown if the external pilot reference signal is correct and a pilot sig-
nal is played back from the tape.
When meter switch (12) is in the "SYNCH" position, the meter is connected to the QSLI, and shows the differ-
ence of phase between the external pilot signal and the playback pilot signal from the tape. Thus if the signals
do not have exactly the same frequency and phase the needle will oscillate. This can be seen on PLAYBACK
(without the loudspeaker). One complete oscillation left, right, left, every 2 seconds corresponds to a speed error
of 1% which can be corrected by the QSLI.
By putting the main function selector in the "LOUDSPEAKER PLAYBACK" position the QLSI is switched on,
and the needle should be stationary. If it continues to oscillate, then the frequency exceeds the synchronizing
capacity of the QSLI.
If the Nagra is equipped with frequency meter circuit QFM, and the needle is stationary and it the pilot indica-
tor shows a white cross, synchronization is practically certain.
There is one exception, however, it the playback frequency from the tape is grossly incorrect (e.g. 100 Hz instead
of 50), the needle will not be able to follow the beat and will remain stationary in the centre of the dial.
If this is suspected, switch to "PLAYBACK". The needle should oscillate. If need be, upset the tape speed by block-
ing the left side tension roller momentarily. If the needle remains in the centre, the recorded pilot signal is incorrect.
The speed varier QSV–2 is very useful in these cases. In attempting to adjust the speed (on slaved playback) the
QSLI has to adjust itself in order to prevent the speed varier from operating. The needle of the meter will show
this adjustment and will prove that synchronization is correct.
Speed Varier QSV–2
This is an external accessory for the Nagra 4.2. It is plugged into the ACC socket (39) on the left side of the
recorder. It enables the speed to be varied manually up to ± 12% The QSV–2 is used for the following applica-
tions:
a) To transfer a tape whose pilot signal originated from a camera the speed of which was out of tolerance.
The QSLI synchronizer allows the automatic correction of speed errors up to ± 2%. It is not
unknown for cameras to have a speed error greater than this tolerance. The speed varier allows the
offsetting at the average speed which will then be corrected by the synchronizer in the normal
manner. Naturally, under these conditions the tone of the sound will be altered, but this is
inevitable.
b) Transfer of a tape whose pilot signal is interrupted. A very convenient method of indicating the start
marks (or end of takes) as well as the take identification, is by short interruptions of the pilot sig-
nal. During these interruptions. the slaving between the Nagra 4.2 and the film recorder is sup-
pressed. It is important that the speed change during the suppression is not brutal, otherwise audi-
ble wow will be heard. To avoid this, it is sufficient to make approximate correction with the aid of
the speed varier and to allow the synchronizer to make a final adjustment to ensure the slaving.
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