- Data Channel
- The part of an ISDN used for communication with the Telco
switch. It is theoretically possible to send packet switched data on this channel as well,
but we have yet to see any equipment that does that.
There is one "D" channel
in each ISDN BRI or PRI.
- DACS
- The system used to transmit text information to Public Radio Stations. Originally the Dial
Access Communications System, the system used a computer in Washington to call a
terminal at each station to transmit the messages. With the advent of the Satellite age
that system has now been replaced by a low power carrier on the PRSS
which transmits the information simultaneously to all stations. This same coordination channel provides demod
and tape machine control using a system called Netcue.
The
system is available to all program providers and public radio stations using the PRSS. This means NPR, PRI,
the various state networks and some semi-commercial providers. There is nation-wide access
via both WATS and SprintNet.
The computer historians will be interested to know, the original speed used on the
system was 110 Baud, printing out on ASR33 terminals. The first Satellite-delivered system
was running at 300 Baud on KSR43 terminals, it was revised to transmit at 1200 Baud and
either Seikosha printers or a DACS capture program running in the background of a PC to
receive the data.
The latest version uses a 64kbps channel to send the information to a SOSS PC computer
that assists with automation duties, clock syncronization tasks, accpepts binary files, as
well as displaying the old-fashioned written text messages from system users.
- Dalet
- A Digital Audio Workstation system as well as the company that manufactures it.
Dalet
is being installed at NPR for the production of news programming. You will soon find
systems in the studios, RCs and edit booths on the second and third floors.
NPR Distribution is also using Dalet for some programming.
Other DAW systems at NPR include those made by AudioVault
and Sonic Solutions.
- dB
- Decibel One tenth of a Bel. The standard unit of measure for AC voltage
used to characterize the performance of transmitted signals.
- dBrn
- Telco unit of noise level, equal to 98 minus the
signal-to-noise ratio of the circuit. The "signal" used for determining the
signal to noise ratio must be +8 dBm. Zero dBrn is -90 dBm. The ultimate signal to noise
ratio is 98 dB.
- DBX 2:1
- Compressor/Expander Used by many organizations as both a recording and transmission
processing system. NPR has several channels of dbx for use on
tape recorders and some study is being done to determine its suitability for use with the
RPU system. IDB and several state networks use this system on
narrow band satellite circuits.
Basically this is a double ended system employing 2:1
compression at the encoder and 1:2 expansion at the decoder. No adjustments, other than
setting level, should be required.
- DBX 3:1
- Compressor/Expander formerly used by NPR and other Satellite
carriers for analog SCPC audio transmission.
This is a double
ended system employing 3:1 compression at the xmit end and 1:3 expansion at the receive
end. No adjustments, other than setting level, should be required. This system is more
susceptible to frequency response anomalies than the 2:1 process. The best results can be
expected on permanent transmission facilities that have very flat frequency response.
- DELIN
- Or D-line An occasional 3.5 KHz IXC.
- Demod
- DeModulator A device that takes a modulated signal and turns it back to
baseband.
- Digital
- In our context, one of a number of coding schemes used to represent an audio signal as a
numeric value for the purpose of storage, manipulation or transmission. The quality of a
digital audio path is related to the coding scheme, sampling rate, word length and any pre-emphasis used. Digital doesn't necessarily mean better,
only different. See also PCM, ADPCM
and Musicam for more information.
- Duplex
- Two simultaneous but opposite-direction circuits between the same two points. Often
called "four-wire" in Europe. International program circuits are normally duplex
with a program circuit one way and a noneq backfeed the other way.
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