DL221 OPERATORS MANUAL
4
CONTROL DESCRIPTION
Both channels of the DL221 are identical and may be used completely independently or
linked for stereo operation. In the linked mode, only the left hand channel controls are
functional and serve as master controls, though the channel bypass switches remain
independent. In linked mode, the compressor / limiters and peak limiters of the two
channels track together to avoid the inevitable image shifting that occurs if the two
channels of a stereo signal are treated independently.
COMPRESSOR
THRESHOLD
(Variable -24 dB to infinity) sets the point at which gain reduction
commences. Signals below threshold pass un-attenuated. NB
‘Threshold’ controls the signal level entering the side-chain and not
the input signal level. This can usually be adjusted on preceding
equipment.
RATIO
is variable between 1:1 (zero compression) 20:1 (limit).
ATTACK
(50µS to 5mS) controls the speed at which the compressor
responds to a rise in input signal level. A slow attack time will allow
transient peaks to escape compression, which can give an artificial
percussion effect on certain signals, whilst the fastest attack time
of 50 µS allows the compressor to respond to the fastest of audio
signals.
RELEASE
(50mS to 5sec) is the time taken for the compressor to recover from
gain reduction. Programme signals are complex, so a complex
release characteristic is required for optimum results. Fast
transients require a fast release time to avoid over limiting effects,
whereas normal programme material should be user adjustable. In
addition to these features, the DL231 contains circuits which
prevent partial recovery between waveform peaks, thus almost
eliminating low frequency distortion when using fast release times.
OUTPUT GAIN
(-20dB to +20dB) is necessary to make up signal level which is lost
during compression.
OUTPUT SWITCH enables the operator to select ‘normal’ or ‘bypass’ for comparison
of input or output levels or ‘S/C listen’ for monitoring any
equalisation which may be applied to the side-chain. EQ. applied in
this way enables frequency conscious compression to be achieved -
particularly useful for de-essing, de-popping etc.
PEAK LIMITER
a separate switchable peak limiter, connected after the output gain
control, complements the operation of the compressor section by
allowing slow attack times and/or gentle compression slopes to be
used, whilst giving complete protection from overload. The limiter
has an internally preset threshold of +6dB (ref +4dB), fast attack (50
µS) automatic release based on programme content and a ratio of
50:1. Gain reduction from limiting is indicated on the display along
with compression, but in addition a LED located beneath the limit
switch indicates the onset of limiting.
