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AM-10HD / Aug 2008
A M - 1 0 H D G U I
HD Output Screen
HD OUTPUT MENU
The HD Output screen contains the controls necessary to fine tune the sound
of the HD output as well as adjust its peak control method and the absolute peak
Output Level.
Source
The HD Limiter may be fed from the output of the five-band AGC/Compressor
(Compressor selection), the output of the 10-band AM limiter (MB Limiter selec-
tion), or the output of the Vorsis Bass Management System (VBMS selection).
When the HD Limiter is being fed from the output of the 10-band FM limiter
complementary de-emphasis is applied if AM NRSC pre-emphasis has been selected
prior to the multiband limiter. This is so that the HD limiter does not have to man-
age the pre-emphasis required for AM.
When the HD Limiter is being fed from the five band AGC/Compressor no AM
pre-emphasis has been applied yet so no de-emphasis is necessary nor applied.
Bandwidth
Sets the maximum bandwidth of the HD channel’s audio path. The US iBiquity
AM HD system typically specifies an HD AM audio bandwidth of 15kHz. Other
applications may use the other settings and therefore we have provided bandwidth
selections for 4kHz through 16kHz in 1kHz steps, plus an Off setting which results
in a full 20kHz audio bandwidth.
HF Protect and HyperMono
Probably one of the most annoying HD AM codec artifacts is the splashy, watery
sound commonly heard when operating codecs at very low bitrates and with audio
material having excessive high frequency content. A static high frequency roll off
would tame this artifact, but the resulting audio would then sound dull on most all
program material. A much better solution is to control how much high frequency
content is permitted to enter the codec and under what conditions, and this is what
HF Protect does.
