Ashly LIMITER/COMPRESSORS CL-100 Manuel du propriétaire - Page 5

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been reached. For verv fast transients, such as hand claps, snare drums, or

other percussive sounds, a very fast attack time is usually desirable so that

the limiter can respond in time to control the peak level. On other types of

program material,

a slower attack time may be preferred.

A too-fast attack

may, on some material, "square off" the top of a waveform, producing a

distorted sound. The Ashly CL Series provides continuously variable attack

times from 200 microseconds

to 20 milliseconds.

Release Time

Another parameter which affects compressor/limiter

performance is

Release time, or the time required for the limiter to restore system gain to

normal after the input signal has fallen below threshold level. Again, proper

Release time will depend on the type of program material being processed

and the way in which the limiter is being used.

When subtle limiting is desired, slow release times are often chosen to

avoid

a condition referred to as "pumping" or "breathing". This occurs when

overall gain is modulated up and down by repeated peaks which are followed

by quieter intervals. If the release time is set too fast, then the overall level

will jump up and down, producing an objectionable

and unsettling effect.

Note that, in some cases, an individual track or channel which seems to be

pumping may sound acceptable when heard in context of a complete mix.

A unique feature of the Ashly Compressor/Limiters is the incorporation

of a double release-time constant. When a conventional compressor/limiter is

adjusted for slow release times, transients such as mic "pops" and record

scratches may cause a severe reduction in gain followed by a slow fade-up,

making the action of the limiter very obvious. With the double time constant,

release from gain reduction after a brief transient is always fast, with a

slower release after a sustained overdrive.

Output Level

provided to restore up to 18 dB of system gain. NOTE: When the unit is in

the BYPASS mode the OUTPUT control still functions.

Bypass Switch

This switch enables you to quickly switch the CL compressor/limiter in

or out of the audio chain, making comparisons between processed and

unprocessed signals easy. When the switch is in the OUT position, all

limiting and compression controls and functions are bypassed, with the

exception of the output control, which continues to function as a

straightforward level control. For all normal compress and limit functions,

this switch should be depressed to the IN position.

Threshold/Gain Reduction Indicators

Five LED's on the CL-50E and CL-100 front panels provide a convenient

visual indication of the amount of gain reduction that is taking place at any

time. As soon as the 0dBV threshold level is reached, the yellow LED

illuminates. Depending on how far the input level rises above threshold, and

the settings of the RATIO, ATTACK, and RELEASE controls, successive red

LED's will illuminate, indicating increasing gain reduction.

Gain reduction is a useful way of expressing compressor/limiter

action.

We have seen that the increase in output level of a compressor/limiter is less

than the increase in input level by some amount. Using a limit ratio, output

level will remain nearly constant as input levels increase above threshold.

With a gentle ratio, say 2:1, input signals above threshold will be "gain-

reduced" at the output by exactly 1/2. Thus, gain reduction can be expressed

as input level increase divided by output level increase. For example,

a +12

dBV input signal that is 3:1 compressed will produce 4 dB of change at the

output, and 8 dB of gain reduction has occurred (12 dB input minus 4 dB

output = 8 dB gain reduction). The -6 dB red LED on the CL-50E or CL-100

front panel would be seen to light up because we are past 6dB reduction, but

not yet to 10dB. Q