page 1 – 6
FM-55 / Aug 2014
G E N E R A L I N F O R M A T I O N
Generic “audio” cable such as Belden 8451 and 9451 may sometimes be used for inter-
connecting AES3 digital audio devices as long as the cable is short. The actual cable length
that will work satisfactorily is determined by many factors including the error correction
and jitter tolerance of the AES3 receiver, the characteristics of the digital cable driver and
the characteristics of the specific cable being used and its length. “Generic” analog audio
cables usually have higher capacitance than digital cable and high capacitance cables can
impair the ability of the AES3 receiver to recover the digital signal without errors. Increased
jitter, dropouts, or no audio at all can be an indication of an improper cable type.
Where to Install the AM-55
The best and really the ONLY location to install the AM-55 is at the transmitter site.
The major benefit of a transmitter site installation is that it allows much tighter control of
modulation peaks.
A transmitter site location has the additional benefit of allowing the use of the AM-55’s
peak processing and asymmetry control to provide maximum modulation control and loud-
ness to your AM signal. The use of the AM-55 in any location other than the transmitter
site is not recommended as the AM-55 was designed to be the very last piece of processing
gear prior to the transmitter.
Ratings Encoders
Field experience has been that Wheatstone audio processors favorably pass the data
watermarking scheme used in the rating service technology, regardless of the aggressive-
ness of the processing being performed.
Insert Point (Future Feature)
For those concerned with the survivability of the ratings encoder watermark, the
AM-55 does have a ratings encoder insert point that places the encoder towards the back
of the audio processor just before the final peak controller. This allows the AM-55 AGC/
Compressor and Limiter to provide a consistent audio signal to the encoder to improve
watermark robustness and encoding reliability.
AC Power Considerations
Please note that in order to enhance its long-term reliability, the AM-55 has no power
switch because all power switches notoriously become intermittent over time without
regular use.
The AM-55 accepts AC line input voltages between 90 and 260 VAC, 50 or 60Hz.
Power consumption is under 100VA.
Although aggressive AC input filtering is utilized on the AC power input it is always
advisable to use external surge protection and an uninterruptible power supply (UPS)
wherever possible, especially where the AC power quality can be in question, such as at
a remote transmitter site.
Power conditioning, surge suppression, and even power backup devices are wise invest-
ments when using sensitive modern electronic devices. The AM-55 is, after all, a highly
specialized “computer.”
The use of a UPS as recommended will protect the AM-55 from short duration power
interruptions and glitches which might otherwise signal it to reboot. When the AM-55
reboots there will be a loss of audio for approximately 15 seconds.
