Nagra PORTABLE ANALOGUE AUDIO TAPE RECORDER Instruction Manual - page 25
4.1. DIRECT AND TAPE CHAINS
GENERAL
Signals coming from the microphone(s), line and mixer inputs, once they are amplified, filtered,
controlled and mixed, form the "Direct" signal, which will be recorded on the tape.
The signal played back from the tape gives, after amplification and equalization, the "Tape" signal.
During recording, the "Tape" signal is that which has already been recorded on the tape, and
therefore is not that which is being recorded.
The modulometer measures the level of the "Direct" signal. It is operational even in the absence of
a tape. On the other hand, there will be no "Tape" signal in this case. When the Nagra is in
playback, the level control potentiometer "Line and Playback" is used to adjust the "Tape" signal.
The "Direct" signal is therefore made up not only of the input signals, but also by the playback
signal. This allows for example, the superimposition of a commentary to the signal being played
back form a tape. On the other hand, the "Tape" signal will always be exclusively the playback
signal from the tape.
The line output amplifier, which also feeds the headphones, can be connected either to the "Tape"
signal or to the "Direct" signal, the choice being made by the "Line and Phones" switch on the front
panel. The loudspeaker amplifier is only fed from the "Tape" signal. Acoustic feedback therefore
cannot be produced, even if the microphones are in service, unless, of course, this takes place from
the headphones.
The Line and Phones snap switch allows meter readings of the playback signal while recording. It
always snaps back into the "DIRECT" position.
AUDIO INPUTS
The Nagra 4.2 has 4 inputs:
a.) two microphone inputs
b.) one asymmetrical line input transformable into 3rd microphone input with the
aid of an external preamplifier.
c.) one mixer input at fixed level
MANUAL LEVEL CONTROL
When using manual level control the position of the microphone potentiometers, which are in use,
adjust the input in such a way that the loudest sounds to be recorded do not exceed the maximum
level. The potentiometers corresponding to the unused inputs should be kept in their anti-clockwise
position.
The active potentiometers can be equally used to give a compression, by increasing the sensitivity
during the soft passages, and vice versa.
LIMITER
The Nagra 4.2 is equipped with a safety limiter, which instantaneously reduces the gain of the
recording amplifier when the signal exceeds the maximum level providing that the RECORD with
limiter position of the Main Function Selector has been selected. This limiting evidently causes
distortion, but it is less objectionable than that caused by saturation of the tape. Normally, the limiter
will only be brought into action when accidents occur. It is possible that, in the middle of a dialogue,
for example, a short but high power sounds exceeding the maximum level can occur. Under these
conditions it is preferable to saturate rather than to limit because the saturation will be practically
unnoticeable due to the short duration of the sound. On the other hand, the limiter requires a certain
recovery time before the normal sensitivity of the chain is re-established. This sensitivity variation