CX335 User Manual v1.0
11
and will generally sound bad in different ways at different
frequencies. For instance, too fast an attack time at low
frequencies will cause distortion as the gain reduction may
change during one cycle. On the other hand, too slow an
attack time at high frequencies will not process the signal
peaks quick enough, resulting in the possibility of system
clipping and lack of speaker protection.
The conclusion is that for most music programme material,
a fixed attack time is virtually useless. Similarly, a release
control that doesn’t track the input programme envelope
will result in audible ‘pumping’ or breathing as the gain
reduction changes.
The CX335 gets over this problem by constantly adjusting
these two crucial ‘parameters’ internally depending on the
level and frequency of the incoming signal. For this reason,
the usual rotary Attack and Release controls found on
most compressors are replaced by a simple two-position
ENVELOPE switch.
For most applications, satisfactory operation will be obtained
with ENVELOPE set to “Normal”. In the “Slow” setting,
the programme-dependent circuitry is modified to allow
fast dynamic peaks through unprocessed; however signals
exceeding the threshold for longer than approximately
one second are still processed. This setting may help to
restore the “punch” of particularly percussive music, but we
recommend the peak limiter is used to provide additional
protection for the amplifiers and loudspeakers.
Peak limiter
Although the compressor may be set to a high compression
ratio to act as a limiter, this may not always be a desirable
solution. The CX335’s separate peak limiter section is
designed to set an absolute maximum level that the output
signal will not exceed a pre-determined level under any
circumstances. The control can set the peak limiter threshold
from +26 dBu (where the limiter has no effect) down to
-6 dBu. The peak limiter is very fast, enabling it to limit any
peaks without audible distortion. If the output signal is so
high as to cause the limiter to operate for more than 20 ms,
the overall system gain is automatically reduced to bring the
signal back within range. The gain is then returned to normal
over a period of approximately one second. The PEAK
control and GAIN controls should be used in conjunction to
ensure that the peak limiter operates only rarely (if at all), if
it is to be used purely for peak protection.
Adjustments
Finding the optimum settings for the front panel controls is
relatively straightforward. However, the audible effect of each
control differs slightly depending on the unit’s Operating
Mode. Each Mode is described below, together with guidance
of how to set the controls for the best compromise
between transparency and protection.
Operating Mode
The CX335’s four Operating Modes are set by the four
possible combinations of the ENVELOPE and KNEE buttons.
The four Modes are summarised in the table below:
SOFT KNEE
HARD KNEE
NORMAL
ENVELOPE
Mode 1: ultra-
transparent control
of SPL and speaker
protection.
Mode 3: precise control
of signal level and speaker
protection.
SLOW
ENVELOPE
Mode 2: very
transparent control
of SPL, but some
peaks allowed through
unprocessed.
Mode 4: the least
transparent mode of
operation to reduce high
level signals, but with more
peaks passed unprocessed.
Mode 1 – Soft Knee/Normal Envelope:
This is the recommended mode for the majority of
situations, yielding the most musical results with the least
perceptible effects on the programme.
For compression only, set THRESHOLD to between 10
and 15 dB below the average input signal level and RATIO
to between 5:1 and 10:1. For compression and limiting, set
RATIO to 20:1 or higher. With programme at the normal
level, adjust GAIN while pressing BYPASS several times, until
the output meters indicate roughly the same level when the
compressor is bypassed as when it is in circuit.
KNEE
THRESHOLD
RATIO
PEAK
GAIN
BYPASS
4
4
0
3
10
- +
8
8
NORMAL
BYPASS
12
12
dB
LIMIT
dBu
6
15
20
0
26
-
NORMAL
SOFT
SLOW
HARD
3
-2
-4
6
2
5
10
20
1.5
1.2
:1
-10
-15
-20
+10
5
0
dBu
ENVELOPE
In this Mode, the higher the input signal, the more
compression will take place. A perceptible increase in
average overall volume should be noted, although the peak
output level should be slightly lower.
The PEAK control adjusts the threshold of the separate
Peak Limiter, and operates independently of the CX335’s
other controls. It lets the user set an absolute limit on the
maximum output level; however, it has the disadvantage
of sounding slightly less transparent than the compressor.
The compressor should be set to provide most of the gain
reduction, while the peak limiter should be thought of as
a ‘safety net’, to protect the system when it is subject to
abuse. The PEAK control should be adjusted by considering
the highest anticipated input level and observing the ‘clip’ (or