Orban OPTIMOD-FM 8600Si, Operating Manual

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OPERATION ORBAN MODEL 8600Si
While this calibration may seem unintuitive, experience has shown that it greatly
reduces calls to Orban customer service complaining that the frequency response
of the transmission path is not flat when in fact the measurement in question
was causing undetected clipping at high frequencies due to preemphasis.
Getting the Bass Sound You Want
Probably the most frequently asked question we get regarding 8600Si setup is “How
do I get a (such-and-such) bass sound?” It seems that individual preference varies in
this area more than anywhere else.
There are no magic formulas. The 8600Si has extremely versatile controls affecting
bass sound and will allow you to get almost any sound you want as long as that
sound respects the laws of physics—or, in this case, the laws of psychoacoustics.
The ear is far less sensitive to bass than to midrange sounds. You can see this for
yourself by examining the classic Fletcher-Munson "equal-loudness" curves. This
means that if you want robust bass, this will take up a great deal of room in your
modulation waveform. This room could otherwise be used for midrange, where far
smaller amounts of energy yield the same amount of loudness. Accordingly, there is
an important tradeoff between loudness and bass—if you want more bass, you will
have to accept either less loudness or noticeably more distortion, which occurs when
the bass waveforms push the midrange and high frequency material into the
8600Si’s final clipper.
There is one psychoacoustic trick you can use to create more apparent bass while us-
ing modulation headroom efficiently. For hundreds of years, pipe organ makers
have tricked the ear into hearing non-existent fundamental tones (which would re-
quire huge, expensive pipes) by replacing them with several, smaller pipes tuned to
the lower harmonics of the missing fundamental. In the 8600Si, you can use the bass
clipper to make harmonic distortion for this purpose. As explained above, the bass
clipper has three settings—
S
OFT
, M
EDIUM
,
AND
H
ARD —that determine the amount of
distortion the clipper makes when its clips bands 1 and 2.
S
OFT provides the purest
sound, but
M
EDIUM and
H
ARD create progressively more distortion on bass. Because
H
ARD can make noticeable voice distortion, the factory programmers prefer
M
EDIUM
for most presets. However, if you are willing to trade off voice distortion against
bass punch, then you could also use
H
ARD .
H
ARD is particularly effective in increasing
bass punch because it flattops bass transients and this allows the waveform to ac-
commodate fundamentals that have a larger peak level (by up to 2 dB) than the
peak level of the flat-top. (The fundamental of a square wave has a peak level 2.1
dB higher than the peak level of the square wave.) In essence, by doing this, your
bass fundamentals can exceed 100% modulation without having the composite ste-
reo waveform itself exceed this level.
The attack time of the band 1 compressor affects bass punch by determining the
amount of bass transient that is allowed to pass through the compressor before the
attack clamps down the rest of the waveform. Any transient that passes through the
band 1 compressor will hit the bass clipper, so slower attack times on band 1 will in-
crease bass punch at the expense of distortion (particularly on voice). The
B
AND
1