Operating instructions

OPTIMOD-AM DIGITAL OPERATION
3-43
you have a very good reason to set the control elsewhere, we recommend leaving it
at the factory settings, which were determined following extensive listening tests
with many types of critical program material.
Bass Clip Mode
sets the operation of the bass clipper to HARD, LL HARD, MEDIUM, or
S
OFT.
 H
ARD operates the clipper like the clipper in Orban’s Optimod-AM 9200. It pro-
duces the most harmonic distortion.
This can be useful if you want maximum bass punch because this setting
allows bass transients (like kick drums) to make square waves. The peak
level of the fundamental component of a square wave is 2.1 dB higher
than the peak level of the flat top in the square wave. Therefore, this al-
lows you to get low bass that is actually higher than 100% modulation—
the harmonics produced by the clipping work to hold down the peak
level.
The square waves produced by this clipper are filtered through a
6 dB/octave lowpass filter that is down 3 dB at 400 Hz. This greatly re-
duces the audibility of the higher clipper-generated harmonics. Never-
theless, the downside is that material with sustained bass (including
speech) will sound substantially less clean than it will with the M
EDIUM or
S
OFT settings. The upside is that these harmonics can extend the per-
ceived bass response of small radios.
Note that the H
ARD CLIP SHAPE control determines how squared-off the
clipped bass waveforms become. (See Clip Shape on page 3-44.)
 LLHARD differs in two ways from the normal HARD mode of the bass clipper:
 LLH
ARD automatically defeats the compressor lookahead. This action
is functionally equivalent to setting the L
OOKAHEAD control to OUT,
except that it reduces input/output delay by 5 ms).
 LLH
ARD prevents the bass clipper from switching to MEDIUM mode
whenever speech is detected. By constraining the system in these
ways, it ensures that the delay is always 17 ms.
To minimize speech distortion, the speech/music detector automatically
switches the bass clipper to M
EDIUM when speech is detected if the Five-
Band structure is active and the B
ASS CLIP MODE is set to HARD. (See “Loo-
kahead” on page 3-53 for more about the speech/music detector.) If the
bass clipper is set to LLH
ARD, the speech/music detector will reset the
clipper threshold to the setting specified by the S
PEECHBCTHR control.
The default setting is “0 dB,” which results in very little bass clipper ac-
tion during speech. This prevents audible speech distortion that this clip-
per might otherwise introduce.
Switching the B
ASSCLIPMODE to LLHARD (from any other mode) removes
five milliseconds of delay from the signal path. Switching can cause audi-
ble clicks, pops, or thumps (due to waveform discontinuity) if it occurs
during program material. If you have some presets with LLH
ARD bass
clipper mode and some without, switching between these presets is likely
to cause clicks unless you do it during silence. However, these clicks will
never cause modulation to exceed 100%.