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Adequate signal-to-noise ratio is one of the characteristics of
a professionally designed and installed sound reinforcement system.
The terms "dynamic range" and "signal-to-noise ratio"
are often used interchangeably, but a closer look reveals that they
are not exactly the same thing. The dynamic range of a sound system
is the difference in level between the highest signal peak that
can be reproduced by the system (or device in the system) and the
amplitude of the highest spectral component of the noise floor.
Every electronic device has a dynamic range that is determined primarily
by the limitations of the power supply and the residual noise level
of the unit. A strong narrow band component in a device's noise
floor will limit the dynamic range of the system.
Signal-to-noise ratio is the difference in level between the average
signal level and the average level of the noise floor. A device
that is being driven to some average out put level with common program
material should have peaks that exceed this level by 10 to 20 dB.
This is why we operate mixers near their "0" indication
on their meter, and the rest of the available voltage swing is reserved
for peaks in the program material.
The "average" level is of importance, because it is what
we listeners (and meters) use to judge the loudness of the program.
If a voltmeter were used to measure the R. M. S. value of the device's
residual noise, the signal-to-noise ratio will be the difference
in level between this value (usually expressed in dBV or dBu) and
the nominal "zero" output level ex pressed using the same
dB reference. This assumes that the device is being driven to its
"meter zero" which is where we like to operate most mixers
to optimize their gain structure.
The dynamic range of a system (or component) is not dependent on
a signal being present. It's just the difference between the maximum
possible undistorted out put level and the highest component in
the noise floor (usually "A" weighted). Signal-to-noise
ratio requires a signal, so it must be measured under actual use
of the system or component. A system with wide dynamic range may
have poor signal-to-noise due to the way that it is operated.
Dynamic range can be used to describe the performance that is possible
to achieve with a system or device, whereas signal-to-noise ratio
might be used to describe what is actually achieved in practice.
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