Nagra IVSJ

This version of the Nagra IV comes up at vintage equipment fairs from time to time. I have even seen one
at a camera fair in South London once. While an interesting and probably much rarer version of the
famous portable audio recorder, this Nagra is a highly specialized instrumentation recorder, actually
rather unsuited to straightforward high-fidelity audio recording. What sets this machine appart is that it
has two 'direct' type wideband recording channels that have a frequency response of 2.5 Hz to 35 kHz,
and one frequency modulated channel with a frequency response of 0 Hz (DC) to 4 kHz. It also has
precision switched input attenuators with a resolution of 1dB (see the image below), an accurately
calibrated 'modulometer' with Peak and RMS scales, and in-built physiological filters type A, B, C and D.
In other words it is actually a precision recording sound level meter to the 'CEI 179 norm', and with a
separate B&K measuring microphone, made this recording measuring instrument a popular tool for noise
and vibration analysis. Portable systems such as these were often to be found measuring the noise
generated by jet engines, aircraft at airports, or the rumble of trains in a tunnel. I imagine that these days a
simple laptop and a digital microphone interface have become the much cheaper modern equivalent, and
hence these unwanted specialized Nagras appear from time to time. They were probably much more
costly than the audio recorder, great to admire in a collection, but are not much use for simple high quality
audio recording.

For a while I did wonder quite what was this difference was between a 'direct' recording instrumentation
standard recorder and a conventional 'audio' recorder. This was because a Racal Thermionic Store Four
recorder I have does seem to make rather fine audio recordings. However, apart from the different ANSI
'instrumentation' standards for record level, track placing and width (though many of the tape speeds are the
same), direct recording takes very careful account of recorded phase and flatness of frequency response. But
more significantly, unlike the audio recorder's use of high frequency pre-emphasis (boost) in record, and de-
emphasis (cut) on playback, to improve the overall signal to noise ratio at some cost to phase performance,
ANSI 'direct' record electronics do not. Leaving out de-emphasis and using special tape heads and electronics
can produce astonishingly flat and wideband record / replay performances, but at an unacceptable cost to the
overall signal to noise ratio for Hi-Fi use.

Click on the above picture for images of the machine's interior.