Message Repeaters and Evacuation Systems 1519specialists), news broadcast services, and visitors infor-
mation services. They are also widely used for employ-
ment hotlines, movie theater schedules, sports score
lines, and weather information lines.
40.4.7 Message-on--Hold Applications for Message
Repeaters
Telephone on-hold equipment is operating whenever we
hear anything but silence when we are put onhold.
There are three basic categories of on-hold equipment:
- Tuners/radios, where the on-hold program is a radio
broadcast. - Cassette players, where the on-hold program is on an
endless loop cassette. - Digital playback systems, where the on-hold program
is stored on solid state memory chips.
Each system has advantages and disadvantages.
While the tuner/radio is probably the least expensive
method of playing on-hold programs, employing radio
programs on-hold has a few pitfalls. For instance, radio
programs include licensed music and retransmission is
illegal for all but very small businesses without paying
licensing fees. The tuner/radio might also be transmit-
ting competitive ads.
Cassette players allow end users to either make their
own on-hold program, or have it made by a professional
on-hold studio. The disadvantages to cassette players
are tape and head wear from dragging the tape across
playback heads and the necessity for head cleaning and
demagnetization every few weeks to slow head wear.
Digital playback units came into use in the 1980s,
primarily because of their high reliability. When the
program is loaded into solid state digital memory chips,
it can be played back continuously with no moving
parts and no wear and tear. The program sounds the
same on the millionth play as it does on the first.
The programming and messages for on-hold players
can be recorded either locally or remotely. Local
recording and programming requires someone on-site to
record the message or load cassette tapes. Some of the
more intelligent systems allow for remote downloading
of the programming and messages using satellite
systems, FM subcarrier audio channels, a standard tele-
phone line, a modem, or the Internet. During playback,
these remote download units have all the reliability
advantages of other digital on-hold equipment. They
have the additional advantage over conventional tape
download equipment that they are completely hands-off
at the installation site. They require no intervention
from on-site store personnel, who may be unwilling or
unable to load in the tape.
Digital on-hold players employ memory chips to
store the program. To produce a frequency response
from 20 Hz–20 kHz would require a tremendous
amount of memory. Telephone lines normally will not
transmit a greater frequency response than
300 Hz–3.5 kHz, therefore it is not practical to increase
the response and the equipment cost to cover a much
wider range.
As is the case with CDs, digital on-hold units sample
the incoming signal many times a second to store the
signal into digital memory. Theoretically, the greater the
samples per second—i.e., the sampling rate—the better
the sound quality. Sampling rate is usually expressed in
kilobits per second (Kbps). Toll quality telephone perfor-
mance (the best performance any telephone network will
allow) is 64 Kbps so there is no need to produce on-hold
units with a sampling rate greater than 64 Kbps.
Sampling rate is only one measure of the audio
quality of a digital downloadable on-hold unit; a
network of filters and frequency compensators also
contributes to the sound quality.
In most cases, nontechnical employees connect the
on-hold equipment to the line and load new taped
music/messages. Some units require no controls, no
level setting, and no start/stop control because the units
employ microprocessors to control all aspects of the
download/play process.
The Bogen HSR series unit is an example of a full
microprocessor-controlled on-hold system. Various
models have a 4, 6, 8, or 12 minutes of memory
capacity. The HSR’s automatic operation assesses the
start and stop point of the audio, sets record levels,
downloads, and goes into play mode automatically. The
unit also incorporates a one-play trigger mode for
making a single message such as store closing.
The Mackenzie Laboratories, Inc. Dynavox series
are on-hold systems that can also can be used as store-
casters. One series has a 3.4 kHz bandwidth for tele-
phones and the other series has a 6.8 kHz bandwidth for
storecast and other wide-band requirements. The bit rate
increases from 96 to 196 Kbps and the sampling
frequency increases from 8 to 16 kHz with the
increasing frequency response. Audio storage requires
16 MB DRAM (dynamic random-access memory) to
record 32 minutes at 96 Kbps and 16 minutes at
196 Kbps. These units have a noise floor and dynamic
range of greater than 70 dB.
Intelligent message repeaters, such as the Instaplay™
series by ALARMCO, can provide on-hold music and
messages, storecasting messages, triggered customer