Roland Stage Amplifier SA-1000 - Manual (Page 15)

15
About the Anti-Feedback Function
Features of SA-1000 ANTI-FEEDBACK
Many previous anti-feedback systems use methods of determining feedback that actually generate feedback in order to detect the
feedback point, resulting in a system that is extremely unpleasant to use.
On the other hand, the SA-1000 employs a newly developed method that does not require generation of feedback, but instead
uses a microphone to capture a calibration signal output from the SA-1000’s own speakers, then performs a feedback analysis to
estimate the feedback point.
■ What is Acoustic Feedback
When sounds output by speakers reenter a microphone, they
end up being output from the speakers at even greater
volume, and as this cycle is repeated, an unpleasant and
uncomfortable oscillating sound is created.
Pointing microphones towards speakers or placing them
near the speakers allows the amplified sounds from the
speakers to enter the microphones again, thus making it even
easier for feedback to arise.
■ To Avoid Feedback
In general, avoiding feedback requires the following
measures:
• Setting output levels so they’re appropriate for the
particular site or room
• Setting connected devices to suitable levels
• Keeping microphones and speakers as distant from each
other as possible, and avoiding placing microphones
such that they are pointed directly at the speakers.
These methods will allow you to suppress the most serious
types of feedback.
In actuality, however, feedback can still occur as you attempt
to achieve necessary output levels, while on the other hand,
moving speakers away to avoid causing feedback can end up
making the sound difficult to hear.
■ Reducing Acoustic Feedback with
the SA-1000 (Anti-Feedback)
The SA-1000 includes the following three built-in functions,
which allow you to achieve an acoustically stable system that
automatically controls the occurrence of feedback and makes
it more difficult for feedback to arise.
Dynamic Function
1 Suppresses feedback that occurs at times when there is
no sound from the microphone.
For feedback generated when no audio is being input via
the microphone (for example, at times when the
performer is not at the microphone), the feedback point
is automatically detected and the feedback is cut with a
dedicated filter.
2 Prevents sudden feedback that occurs when the
microphone is in use.
This system automatically cuts out feedback that crops
up suddenly due to changes in the surroundings or
movement of the microphone, using an extremely
narrow filter to minimize alterations in the sound
quality.
Safety Margin Function
3 Conditions are calibrated automatically to help prevent
feedback.
Frequencies prone to feedback will change depending on
the microphones used, the placement of the SA-1000
(speakers), and the SA-1000’s output level settings.
The SA-1000 measures conditions first to detect these
frequencies and secure a sufficient safety margin (i.e., an
ample margin of gain before feedback starts to occur).
The entire process, from measurement to securing of the
safety margin, takes only a few seconds.
The dedicated filter is optimally processed for each
feedback point, resulting in an acoustically stable system
that minimizes tonal changes.
Relationship Between Anti-Feedback Functions
and Buttons
ON/OFF Button: Switches Dynamic function on and off
AUTO Button: Activates the Safety Margin function
■ About Speaker and Mic Placement
Conventional PA systems generally require performers using
mics to stand behind speakers to avoid feedback. This makes
it difficult to hear the sound from the speakers, making
comfortable monitoring impossible.
The SA-1000’s internal anti-feedback system suppresses
feedback, allowing performers to monitor the sound in
comfort, even when standing in front of the speakers.
• Howling could be produced depending on the location of
microphones relative to speakers. This can be remedied
by:
1. Changing the orientation of the microphone(s).
2. Relocating microphone(s) at a greater distance from
speakers.
3. Lowering volume levels.
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