User manual

7 SHARK FBQ100 User Manual
Monitoring P.A.
+4 dBu Line
Monitor
Out
Master Out
Fig. 2.4: Two SHARKs in the monitor path
2.1.5 The SHARK used in single channels and subgroups
Whenever you want to make sure that wanted feedback such as the feedback
sounds produced by a guitar won’t be removed, you should insert one or several
FBQ100 into “feedback-prone” single channels (e.g. vocals) or subgroups of your
mixing console! Route all channels that are susceptible to feedback (e.g. all vocal
mics) to one or several subgroups, in which you insert one or several SHARKs.
Inthis way, all channels that are less liable to produce feedback (e.g. those
carrying line-level signals, or instrumental microphones with lower volumes)
can pass the console unaltered, while only critical microphone channels are
controlled by the FBQ100. Thus, you can protect your sound reinforcement system
against feedback and still use wanted feedback sounds.
Mixer
Insert Point
Send
Return
Out
Return
Send Ground
Ground
+4
dBu
Line
In
Fig. 2.5: The SHARK in the insert path
2.1.6 Automatic “tuning in” of P.A. and monitor systems
With the FBQ100 you can improve the protection against feedback even before
a concert begins, simply by “tuning in” your sound reinforcement system:
oncethe system has been installed and set up, open all microphone channels
and monitor paths, then enable FILTER LEARN mode on your FBQ100. The SHARK
generates short feedback-causing signals, which are then sent back to its input
and suppressed by the lters. These lters are permanently assigned and can
be recongured as free searching lters only by means of a RESET. Without the
SHARK you could raise the overall volume level only until the rst feedback
occurs. But with the FBQ100 you’ve got considerably more headroom! Please note
that the FILTER LEARN mode is limited to about 15 seconds.
If you are using not just one FBQ100 for the monitor path, you should employ
some additional units to safeguard critical signal paths. Experience has shown
that during a concert the musicians on stage usually want their instruments
made louder in the monitors. With the SHARK you can raise the volume without
running the risk of feedback. When the concert begins the FBQ100 automatically
tracks and removes varying feedback signals produced by “moving”
vocalmicrophones.
2.2 The feedback destroyer in the SHARK
The SHARK identies feedback by splitting the entire frequency spectrum
(20 Hz to 20 kHz) into sections of 1/60 of an octave and determining the level
of each of these bands. The values calculated are then referenced to the level
of the overall signal. The resulting level dierence determines whether or not
a lter is set. The SHARK allows you to adapt these decisive parameter to your
needs: withina range from 1 through 100 you can edit the feedback detection
sensitivity. Thestandard setting is 50, which ensures the best possible detection
of feedback for the majority of applications. For speech-only applications you can
raise the feedback detection threshold towards 100, which enables the algorithm
to detect and remove feedback even more quickly. Vice versa, lowervalues
provide for a more stable feedback suppression responding less to wanted
feedback-like signal portions produced by guitars or keyboards.
In FILTER LEARN mode, feedback is generated and suppressed automatically.
Whenever it detects feedback, the FBQ100 selects the lter parameters
automatically to eciently remove the feedback. As the lter is set to the
frequency detected, this mode is ideally suitable for suppressing constant
feedback frequencies produced by “xed” microphones, e.g. those used on
drums. Once set, the lters automatically enters lock mode, i.e. the frequency
remains xed but width and depth of the lter are still being adapted to the
signal. The lter width is enlarged whenever the feedback frequency shifts
slightly. If feedback persists, gain is reduced even more and kept low to prevent
feedback from recurring.
All microphones that are moved during a performance (e.g. hand-held
vocal microphones) are usually susceptible to varying feedback frequencies,
whichshould be suppressed in automatic search mode (entered when you
power up the SHARK). Much like in FILTER LEARN mode, a lter automatically
determines the ideal settings for all parameters, in order to suppress feedback.
However, onceall lters have been set, the lter rst activated gets reset to
automatic search mode. Thus, the SHARK makes sure that there is always one free
lter to identify and remove new feedback frequencies. If your music contains
wanted feedback elements (e.g. guitar feedback), the SHARK will suppress these
too, because it is impossible from a physical point of view to distinguish wanted
from unwanted feedback. Section 2.1.6 provides some information on how to get
around this physical problem.
2.3 The integrated delay
In addition to speakers on or near the stage, major-scale installations often
have speaker groups positioned at a distance to the stage or own above the
audience, in order to provide listeners away from the stage with direct sound.
However, since sound needs some time to travel around (343.6 m/sec at 20°C,
acceleratesby 0.6 m/sec per °C), it reaches the audience not simultaneously
but gets delayed by a certain amount. To make up for the dierent run times
between stage and remote speakers, the latter must be provided with an
electronically delayed signal, which is usually done by means of special-purpose
Delay devices. Youwon’t need them, however, when you’ve got a SHARK,
asthe FBQ100 integrates a Delay Line circuit giving you the same convenience
of operation as dedicated devices. Simply measure the distance between the
various speaker groups and enter this value (in meters or feet). Chapter 2.1.3
shows you how to wire the FBQ100 in this type of application.