Built-In Calibrated Bypass Test Mode; Monitoring On Loudspeakers And Headphones - Orban OPTIMOD-FM 5500 Operation Manual

1-23
OPTIMOD-FM DIGITAL INTRODUCTION

Built-in Calibrated Bypass Test Mode

A BYPASS Test Mode is available to transparently pass line-up tones generated ear-
lier in the system. It will also pass program material, with no gain reduction or pro-
tection against overmodulation. It can transparently pass any line-up tone applied
to its input up to about 130% output modulation, at which point clipping may oc-
cur.

Monitoring on Loudspeakers and Headphones

In live operations, highly processed audio often causes a problem with the DJ or
presenter's headphones. Some talent moving from an analog processing chain
will require a learning period to become accustomed to the voice coloration caused
by "bone-conduction" comb filtering. This is caused by the delayed headphone
sound's mixing with the live voice sound and introducing notches in the spectrum
that the talent hears as a "hollow" sound when he or she talks. All digital processors
induce this coloration to a greater or lesser extent. Fortunately, it does not cause
confusion or hesitation in the talent's performance unless the delay is above the
psychoacoustic "echo fusion" (Haas) threshold of approximately 20 ms and the tal-
ent starts to hear slap echo in addition to frequency response colorations.
The normal delay through the 5500 is about 15 ms. A 15 ms delay is comfortable for
most talent because they do not hear echoes of their own voices in their head-
phones. Further, the 5500 offers a second, ultra-low-latency multiband structure
with a delay of about 5 ms. Although this does not offer the same favorable trade-
off between loudness, presence, and low distortion as the optimum multiband struc-
ture, it is available for use in situations where a given individual cannot tolerate the
15 ms delay of the optimum structure. (However, management should carefully con-
sider whether compromising the sound of the radio station for its entire audience is
an acceptable price for indulging a given personality's demands.)
Because of the availability of both optimum and low latency structures, customers
can confidently replace an older, low-delay processor with the 5500 with no studio
wiring changes. Moreover, off-air cueing of remote talent is routine.
A better solution to the monitoring conundrum is this: The 5500's analog outputs
can be switched to provide a low-delay monitoring feed while still keeping the op-
timum multiband structure on-air (by using the digital or composite output to drive
the transmitter). The monitor feed has no peak limiting and thus cannot drive a
transmitter, but its 5 ms delay is likely to be more comfortable to talent than the 15
ms delay of the optimum processing chain because of less acoustic comb filtering.
If the talent relies principally on headphones to determine whether the station is on
the air, simple loss-of-carrier and loss-of-audio alarms should be added to the system
when the 5500's monitor output is used. The 5500 can be interfaced to such alarms
through any of its eight its GPI remote control inputs, cutting off the low-delay au-
dio to the talent's phones when an audio or carrier failure occurs.