Orban OPTIMOD-FM 8700, Operating Manual

Page: 207 / 390

OPTIMOD-FM DIGITAL OPERATION
3-37
To prevent introducing unnatural coloration in male speech, the subharmonic syn-
thesizer is defeated when the automatic speech/music detector detects speech.
It is important to understand that material below 50 Hz takes up lots of peak level
to produce significant loudness. Moreover, the close spacing of psychoacoustic
“equal loudness“ curves
2
below 50 Hz means small changes in amplitude lead to
large change in subharmonic loudness. The unpredictability of receiver bass re-
sponse means that the perceived loudness of subharmonics is highly receiver-
dependent. Because of the amount of peak level they use up, subharmonics will al-
ways make a broadcast sound quieter for a given amount of processing arti-
facts/distortion—they use up peak level that otherwise could be dedicated to audio
to which the ear is more sensitive. (This is an inevitable effect of the equal-loudness
curves.) For all these reasons, it is wise not to overdo subharmonic synthesis.
Note that when you apply an L+R sinewave at a frequency between 50 to
90 Hz to the 8700i’s input, the 8700i’s speech/music detector will detect
this as “speech,” so no subharmonics will be produced. To test the sub-
harmonic synthesizer with tone, there must be at least 2 dB of level dif-
ference between the left and right inputs. In other words, be sure that
the speech/music detector is indicating “music” in the 8700i PC GUI.
Stereo Enhancer Controls
The stereo enhancer is common to the FM and HD processing chains. You can oper-
ate it in one of two modes or “styles.” The first emulates the Orban 222 analog ste-
reo enhancer, while the second mode, called Delay, emulates a popular enhancer
from another manufacturer that adds a delayed version of the L–R signal to the
original L–R to create stereo enhancement. (See Stereo Enhancement on page 3-8 for
more information.)
Both modes have gating that operates under two conditions.
2
The equal-loudness curves are popularly known as “Fletcher/Munson” curves, alt-
hough these have been superseded by ISO 226:2003. The image was taken from
en.wikipedia.org.
Stereo Enhancer Controls
Basic / Intermediate Name Advanced Name Range
Amount Amount 0.0 ... 10.0
Enhancer In / Out Out / In
Ratio Limit Ratio Lim
70 … 100%
Diffusion Diffusion Off, 0.3 ... 10.0
Style Style 222 / Delay
Depth Depth
0 … 10
Table 3-3: Stereo Enhancer Controls