Getting The Bass Sound You Want - Orban OPTIMOD-FM 5500 Operation Manual

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OPERATION

Getting the Bass Sound You Want

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.
Probably the most frequently asked question we get regarding 5500 setup is "How
do I get a (such-and-such) bass sound?" It seems that individual preference varies in
this area more than it does anywhere else.
There are no magic formulas. The 5500 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 effusive bass, it is going to 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, the distor-
tion occurring when the bass waveforms push the midrange and high frequency ma-
terial into the 5500's final clipper.
There is one psychoacoustic trick you can exploit to create more apparent bass while
efficiently using modulation headroom. 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 5500, you can use the bass
clipper to make harmonic distortion for this purpose. (The B-C
termines the shape of the harmonic spectrum that is introduced by this gambit.)
Further, the bass clipper is particularly effective in increasing bass punch because it
flat-tops bass transients, and this allows the waveform to accommodate fundamen-
tals 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.) Bass fundamentals can thus exceed 100% modulation
even if the composite stereo waveform does not exceed this level.
The attack time of the band 1 compressor also affects bass punch by determining
the amount of bass transient that is allowed to pass through the compressor before
the attack clamps down on 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 increase bass punch at the expense of distortion (particularly on voice).
The BAND 1 ATTACK TIME settings in the factory presets have been adjusted with
this tradeoff in mind, but you might like to make a different one. Further, the
S B C T
PEECH ASS LIPPER
control exploits the 5500's speech/music detector to
HRESHOLD
ORBAN MODEL 5500
control de-
S
L HAPE