MACKIE M800 - Manual (Page 17)

17
LIMITER
LIMITER ON (TYPICAL). This is the normal
configuration with protective limiting.
LIMITER OFF is without protective limiting.
The limiter is not designed to alter your
sound — it’s just there to protect your speakers
from the effects of clipping. Its effect is virtually
transparent, meaning you probably won’t even
notice any audible difference. We recommend
that you leave it engaged, hence the
TYPICAL
label below it.
If you’re working at quiet levels all the time,
or you’ve already placed a compressor/limiter
in the signal path, or if you just hate compres-
sion, you can leave the limiter out of the
circuit. By design, the limiter is out of circuit
when not called upon.
The limiter works independently on each
channel. It senses when the amplifier channel
is about to be overdriven and attenuates the
overall level just enough to keep the signal
from clipping. Clipping occurs when the output
voltage no longer linearly follows the input
voltage and simply stops. This causes a sine
wave to “square off,” and the average power go-
ing into the speaker is roughly double that of a
sine wave. Square waves sound awful, and
could possibly damage your speakers and/or
your reputation.
Sample Audio signal
Clipped Audio signal
Clipped 'do
time
A
C
v
olts
time
A
C
v
olts
V+
V–
0
As the amplifier output volt-
age increases, it will
eventually run into the inter-
nal DC power supplies and
start to flatten out. The flat
tops represent a DC voltage
reaching your speakers, which interrupts the
natural movement of the speaker’s voice coil.
High frequency harmonics are also produced
which can play havoc with your tweeters.
Speakers are designed to handle good clean
continuous signals, but give them a clipped
signal and even high powered speakers can be
damaged. For example, a 100 watt amplifier
that is clipping, can damage speakers that are
rated at 400 watts.
The limiter is especially handy when you’re
working with loud output levels. Having the
signal spikes (kick drum, for instance) attenu-
ated a bit can actually increase the apparent
loudness of the overall mix without diminish-
ing the “power” behind the spikes.
It is also a useful protection device for those
unexpected moments, such as a mike stand
falling over, dropping the tone arm, or an
attack of killer feedback.
Be Forewarned: With the
limiter engaged, you can
still overdrive the amplifier
into clipping and cause
distortion. It just takes a
stronger signal to do it. So
even with the LIMITER turned on, you must pay
attention to the OL LEDs.