Symetrix 528 - Defining Dynamic Range; Dynamic Range as a Specification; Dynamic Range of Sounds and Siiinals

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1.5 Defining Dynamic Range
To begin a discussion of dynamic range processors it's necessary to have a working
definition of dynamic range. The term is really self-descriptive, but has two distinctly
different uses:
1. To describe the actual range of signal fluctuations that are going
through the equipment, and
2. To define the maximum allowable range of signal fluctuations that can
be put through the equipment.
The usual unit of measure for audio signals is the decibel (dB).
1.6 Dynamic Range as a Specification
The maximum usable range of operation for a particular circuit or piece of gear is the
distance in dB between the noise floor and the maximum output level. In this context,
dynamic range is used as an equipment specification.
Noise floor is defined as the lower limit of a circuit's operating level, and is a function
of its self-generated electrical noise. Very noisy circuits have a high noise floor, quiet
circuits have a low noise floor. The maximum output level is the upper limit of the
operating level, and is the level at which clipping begins . To put levels in perspective
they must be referenced to some nominal operating level, like OdBm. That's why noise
specs are stated as minus something.
In the case of the 528, noise is refered to the input, and stated as equivalent input
noise (EIN). The noise specification is ll'iven this way because the gain of the 528's
input stage is variable, so the actual signal-to-noise performance of the unit becomes a
function of how much gain is used in the preamp . To find the signal-to-noise ratio at
OdBm output, subtract the preamp gain from the EIN.
Sinoe maximum output le vel is usually lrJ'eater than OdBm, it's stated as plus something.
The 528's maximum output level is +24dBm, which is 24d8 above OdBm. The difference
between the noise floor and the onset of clipping is the dynamic range. To find the
528's dynamic ranll'e with SOdB preamp gain, subtract -87 from +24. llldB is the dynamic
range.
1.7 Dynamic Range of Sounds and Signals
The other definition of dynamic range describes actual level changes, or the range over
which signals fluctuate. The signals under discussion here are electrical representations
of sounds, so it follows that sound has dynamic range. The dynamic range of the human
voice, from a whisper to a shout, is well over lOOdB. So a microphone will convert the
sound pressure of a the voice ll'Oing from a whisper to a shout into an electrical output
signal with a dynamic range of well over lOOdB.