Specifications

9
Operating Manual - CLX-52 and CLX-51 Compressor/Limiter
5. As soon as the first feedback frequency has
been removed, the Ashly CLX unit will automatically
bring up system gain until another feedback point is in-
duced. Repeat the equalization procedure until it becomes
impossible to distinguish individual, predominant feed-
back frequencies.
6. Return all mixer, EQ overall gain, and com-
pressor/limiter gain controls to normal settings.
7.2 Recording
The Ashly limiter can be used to prevent tape
saturation in analog recording. Also, with modern trends
toward inexpensive digital recording, it remains neces-
sary to protect against input overload. With digital re-
cording, the information stored on tape, hard disk, optical
disk, etc., is either a 1 or 0, so actual signal level on the
tape is not the concern it is with analog recordings, in
fact it is not even a user controllable parameter. What is
of concern however, is the signal level applied to the A-D
(analog to digital) converters. If clipping occurs at the
converter input stage, the resulting distortion is most un-
pleasant, and will be recorded digitally as if they were
part of the original audio signal, forever mixed with the
audio. To prevent converter distortion while preserving
the extended dynamic range of digital recording, look up
the max input level of your recorder/converter and set up
the limiter as follows:
1. Set Gain to 0.
2. Set Threshold to 2-3 dB below max
converter input.
3. Set Ratio to 10.
4. Set Attack to 2 mS.
5. Set Release to .2 Sec.
6. Set Output level to 0.
If you are exceeding threshold frequently, your
input signal is probably too high and should be turned
down. Of course, every situation is different, so experi-
mentation before final recording is always a good idea,
but this is a good starting point.
To obtain a gentler limiting action at the expense
of some dynamic range, decrease the threshold to -15 and
the ratio to 3-5. This is also a good starting point for
analog recording.
De-Essing
A special type of saturation problem often en-
countered in recording is the sibilant (Ssss) sound of the
human voice. High frequency, sibilant sounds can reach
very high energy levels, so that a voice that is otherwise
undistorted breaks up on the esses, producing a raspy, un-
desirable sound. With analog recording to magnetic tape,
high frequencies tend to saturate the tape sooner, and com-
bined with the internal high frequency boost (record pre-
emphasis) on standard tape decks, the need to control
sibilants becomes apparent.
The solution is frequency-dependent limiting,
which is easily accomplished with the CLX unit. By in-
serting an equalizer into the Detector Patch point and
boosting the equalizer at high frequencies in the vicinity
of the sibilant, the limiter’s detector circuit becomes more
sensitive to this particular range of frequencies, and so
will limit the bothersome sibilants more than other fre-
quencies.
Realize that this technique is very different from
simple equalization. Equalizing a sibilant vocal by cut-
ting high frequencies would result in a loss of important
high frequency information at all times, whereas de-essing
has no effect whatsoever on the signal except at the in-
stant of the sibilant. At that moment, the Ashly limiter
will reduce overall gain. Frequency response is unaf-
fected, and the sibilant is controlled.
7.3 Broadcasting
Compression has long been used as a tool to make
an audio signal appear louder. A good example is in broad-
casting, where competing stations with identical trans-
mitters and power attempt to sound louder than each other.
Since they are all restricted with respect to maximum au-
dio level (modulation), their best tactic is to squeeze the
dynamic range of their programs to just a few dB. The
audio output level of the station virtually never changes,
and the listener perceives this continuous high-level sound
as being louder than the same material in an uncompressed
form. Although both compressed and uncompressed pro-
grams reach the same peak levels, the compressed signal
stays near peak level more of the time, and thus sounds
louder. This technique makes the broadcast more intelli-
gible over the road noise in your car, and increases the
geographical area over which the broadcast is audible to
the listener. A similar, if less pronounced, effect can be
used in sound reinforcement and recording applications.