Ashly DPX-200 Operating Manual - Page 6

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1. Dimensions and Schematics

Operating Manual - DPX-200 Parametric Equalizer - Compressor/Limiter

be noted that an infinite ratio setting is likely to cause

noticeable side effects in the sound, and may not be us-

able on programs where subtle control is desired.

6.4 Attack Time

The response of the compressor/limiter to signal

levels above threshold is further defined by the attack time

control. Attack time is the amount of time it takes to

attenuate the output level after threshold has been

reached. For very fast transients, such as hand claps, snare

drums, or other percussive sounds, a fast attack time is

usually desirable so that the limiter can respond in time

to control the peak level. On other types of program ma-

terial, a slower attack time may be preferred. An abrupt

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

waveform, producing a distorted sound. The DPX-200 pro-

vides continuously variable attack times from 200 micro-

seconds to 20 milliseconds.

6.5 Release Time

Another parameter which affects compressor/lim-

iter performance is release time, or the time required 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 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 all Ashly compressor/limit-

ers is the incorporation of a double release-time con-

stant. When a conventional compressor/limiter is adjusted

for slow release times, transients such as mic "pops" 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 af-

ter a brief transient is always fast, with a slower release

after a sustained overdrive.

6.6 Output Level

Output level control is provided to fully cut or

restore up to 18 dB of system gain. For unity gain, set

the control to 0. NOTE: When the compressor/limiter is

switched out, the output control still functions.

6.7 In/Out Switch

This switch enables you to quickly hear the com-

pressor/limiter in or out of the audio chain. When the

switch is in the out position, all limiting and compres-

sion controls and functions are bypassed, with the excep-

tion of the gain and output controls, which continue to

function as straightforward level controls.

6.8 Threshold/Gain Reduction Display

As soon as the threshold level is reached, the yel-

low LED illuminates. Depending on how far the input

level rises above threshold, successive red LED's will il-

luminate, indicating gain reduction. Gain reduction can

best be described as the difference between input level

and the resulting change to output level. For signals

below threshold, there will of course be no gain reduc-

tion, that is, a 10dB increase in input will yield a 10dB

increase in output. For signals above threshold however,

output level will increase only to the extent that the ratio

control allows. With a high ratio, say 20 or so, it will take

20dB of increased input level to increase output level by

1dB. With a gentler ratio of 3:1, input signals above

threshold will be "gain-reduced" at the output by 1/3. In

other words, with threshold set at 0dB, a signal peak at

+12 dBV that is 3:1 compressed (ratio at 3) will produce

only +4 dB (12 3) at the output, and 8 dB of gain reduc-

tion has occurred (12 dBV input minus 4 dBV output=8

dB reduction.)

6.9 Input/Output Meter Select

While the gain reduction display accurately rep-

resents the action of the limiter, comparing input to out-

put levels in real time is somewhat more intuitive, and is

made simple using the input/output meter select switch.

(Use Mono Plug For Ducking)