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Glossary135
headphone volume to diminish by a preset amount whenever a talk key is activated. This can help
to prevent occasional feedback between the speaker and microphone due to volume settings,
microphone placement, etc. For setup and usage, search for “Speaker Dim” in the keypanel
manual index.
Distortion
Distortion is the effect when the output of an electronic device contains undesired signals that
were not present at the input. This is assuming that the electronic device is supposed to be a linear
device. The undesired signals have a frequency or frequencies that are related to the input signal.
If the frequency(ies) is/are harmonically related to a single frequency input, then the undesired
signal is ‘harmonic” distortion. If the signal is the sum or difference of two input frequencies, then
the distortion is called “intermodulation” distortion. If the distortion is the result of a pulse or step
input, and the frequency(ies) is/are related to sums and differences of the frequencies determined
by the Fourier transform of the input pulse or step input, the distortion is called “transient
intermodulation distortion”. Distortion can occur both in active devices (e.g. amplifiers) or
passive devices (e.g. transformers). Harmonic Distortion is measured in percentages or decibels
below the fundamental signal. For example: a distortion of 0.1 percent is “60 dB down”.
Intermodulation Distortion requires two input signals (say 1000 and 400 hertz) to be inserted and
the sum and difference to be measured.
Double Headset
Headset with intercom in one ear and program in the other.
Double-Muff
Headset
Headset with two earphones plus a microphone. It can be connected monaurally (same
information, both ears) or binaurally (separate feed each ear). In binaural operation, the feed can
be intercom in one ear and program in the other, or intercom channel A in one ear and intercom
channel B in the other ear. Channels A and B are either conference line channels or other
intercom feeds. To get a binaural feed requires a binaural/stereo capable user station such as
BP320, BP325, Model 802, Model MCE325, or any station so optioned.
Drain Wire
An uninsulated wire in contact with a shield throughout its length, and used for connecting
(“terminating”) the shield.
Dry Pair / Dry
Line
A dry pair or dry line is a communications line that has audio signals but no direct current (DC)
voltage or current.
DSP
Digital Signal Processor. Usually a microprocessor with two memory addressing capability. One
memory is the program memory which tells the microprocessor what to do, and the second
memory contains: data to be processed, intermediate results, and final results. The advantage of a
DSP is its speed. It is fast enough to process analog (or audio) signals in real time, and is often
used in that application. Some applications are system to system interfaces (e.g. Telos “Link” for
interfacing a standard telephone line to an RTS™ Systems TW Intercom line).
Dual Listen
This is either an option or feature of intercom user stations. Dual listen permits an operator to
listen to two channels at once. This may be a mix of two channels to one ear, or in a binaural or
stereo user station, one channel can be assigned to one ear and the other channel to the other ear.
Dual Listen could also be an intercom channel and a program audio source. The dual listen pots
are functionally configured in one of three ways: 1. One pot controls the audio of the channel
actively used, and the second pot controls the audio of a monitored channel. 2. One pot is always
one channel and the other pot is always the other channel. 3. On three channel systems, operation
is similar to 1. except if the active channel and the monitored channel coincide, the monitor feed
is blanked out to prevent a 6 dB increase in volume and feedback.
Dual Listen
Option
An option for user stations that allows a monaural mix of two channels. Usually the station has
two volume controls, sometimes two concentric volume controls.
Duplex /
Simplex
See Full Duplex, Half Duplex, or Simplex.
Dynamic
Microphone
Converts sound pressure waves to electrical signals by means of a coil attached to a diaphragm
moving in a magnetic field.
E
E
A symbol for voltage used in electronics, and engineering. Also used as the symbol for the
electric field (volts per meter).