Functions as important
as recording require for their perfect execution, some kind of indication more
precise than the operator's own ear, so almost all the devices on the market
incorporate some kind of modulation indicator. The most common are:
A) The meter
This is simply a
galvanometer equipped with a bridge rectifier; Therefore its indication is only
valid for average signal values. They are usually provided with graduated
scales. One from 0 to 100 and the other from -20 to +3 VU. The zero of the VU
scale corresponds to the 100 x 100 scale of the other scale; In electronic
terms a change of level of 1 VU (volume unit) equals a graduation of 1 dB.
Therefore the meter is not so useful when it is required to know the
instantaneous values of the signal.
B) LED indicators.
When recording a
normal music program it may happen that during certain very short periods of
time the signal level is very high and saturates the recording causing the
corresponding distortion. To faithfully follow the variations of the signal to
be recorded, some manufacturers use a group of LEDs in series that are
illuminated when the signal reaches a certain threshold level (which is
indicated in the scale) preset for each of them.
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