SQN-4S IVe User's Handbook
11. AUDIO LEVEL METERS The basic type of metering employed on the SQN-4S is the Peak
Programme Meter (PPM). This was chosen as providing the maximum information about the
relationship between the signal level and the overload point of the recorder. Admittedly, peak meters
do not necessarily give a true representation of the loudness of the signal and some recordists prefer
the VU type of meter which we can also provide. The meters can only give a useful indication of the
recording level when the combination of mixer and recorder has been calibrated. Each meter is
permanently illuminated while the mixer is switched on, allowing operation in dim light. The
illumination requires minimal current from the batteries.
For those unfamiliar with the BSI (BBC style) PPM scale, the intervals between scale graduations
represent a 4dB difference, so that with the nominal Line Level (0dBu) represented by 4, the nominal
Peak Output Level of the mixer (+8dBu) occurs at 6 on the scale. This 'Nominal Peak' is a
simplification of the arguments, since in practice the BBC has adopted various preferred peak levels
for different sound sources and even individual musical instruments. Other PPM scales have not
followed the BBC design and are all expressed in decibels, which makes them more readily
intelligible. They also usually feature a TEST arrow at 0dBu (0.775V) for calibration purposes. The
'nominal peak' level referred to above tends to be seen as +6dB where the scale is calibrated in 3dB
steps (e.g. the 'Nordic Norm' pattern adopted by the Scandinavian Broadcasting Consortium) or +8dB
where calibration is in 4dB increments (e.g. the SMPTE 'preferred' scale published in 1989 where this
peak level is scaled as '0').
VU meters also vary in their calibration. The original VU measured zero at zero dBm in a 600 Ohm
system. Modern practice, based originally on the improved high level performance of analogue
recording tape, is to place zero VU at +4dBm. Either calibration can be provided and will be noted on
the mixer baseplate.
12. OUTPUT LIMITERS Location recording frequently puts the recording engineer in a situation in
which he or she has no control over the ambient sound level. Accordingly, the SQN-4S has been
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