OPTIMOD-FM OPERATION
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output. Simultaneously, this HF rolloff may reduce high frequency artifacts in the rela-
tively low bite-rate codec used in the iBiquity HD Radio system.
See About HD in Section 2 of this manual for a complete description of all HD setup and
subjective adjustment controls.
Input/Output Delay
The algorithmic improvements in the 8400 have one significant cost—the input/output
time delay is a minimum of approximately 15 ms and can be as high as 40 ms, depending
on the setting of the
BassClpMode control. To make intelligent decisions about how to
process, the 8400 needs to look ahead at the next part of the program waveform. (Slowly
changing bass waveforms require particularly long look-ahead delays.) As digital on-air
processing advances further and further from its analog roots, this is the inevitable price
of progress.
20 ms is below the psychoacoustic “echo fusion threshold,” which means that talent will
not hear discrete slap echoes in their headphones. This means that they can monitor com-
fortably off-air without being distracted or confused.
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,
which introduces notches in the spectrum that the talent hears 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, where the talent
starts to hear slap echo in addition to frequency response colorations.
Summary
The 8400 provides numerous important advances over the digital signal processing in
Orban’s popular 8200. By devoting over five times the DSP processing power to the
problem, the 8400 reduces bass distortion, opens up high frequency response, and pre-
vents audible clipping distortion on difficult program material. Added stereo enhance-
ment, high frequency enhancement, and composite peak control complement the basic
processing improvements. Together, they provide the most powerful and effective on-air
FM processing system that Orban has yet created.
Customizing the 8400’s Sound
The subjective setup controls on the 8400 give you the flexibility to customize your sta-
tion’s sound. Nevertheless, as with any audio processing system, proper adjustment of
these controls consists of balancing the trade-offs between loudness, density, and audible
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