Audio Engineering

68 Chapter 2

2.19.4 Reading Apparent VU Levels

Volume indicator instruments can be used to read apparent or relative levels. If, for
example, you know that overload occurs at some apparent level, you can use that reading
as a satisfactory guide to the system’s operation, even though you do not know the true
level. When adjusting levels using the instrument to read the relative change in level,
such as turning the system down 6 dB, you do not need to do so in true level readings.
Instrument indication serves effectively in such cases.

When being given a level, be sure to ascertain whether it is:

1. An instrument indication.


2. An apparent level.


3. A true level.


4. A relative level.


5. A calibration level.


6. A program level.


7. None of the above but simply an arbitrary meter reading.

Special Note: Well-designed mixers have instruments that indicate the available input
power level to the device connected to its output. Such levels are true levels.

2.20 Calculating the Number of Decades in a Frequency Span ......................................

T o fi nd the relationship of the number of decades between the lowest and the highest
frequencies, use the following equations:

HF

LF

..

..

 101 1 decade (2.42)

therefore

HF

LF

HF LF

x

.. x

..

In.. In..

In

decades

 decade





10

10

(2.43)