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input goes up 10dB but the output only goes up 1dB, then the compression
ratio is "10 to 1". In a theoretically ideal compressor, this ratio is the same
for any size of signal above the threshold but for that to be true, the gain cell
and its control circuitry must be perfectly linear over a very wide range. In
practice only compressors based on VCAs and digital potentiometers are
likely to behave in this way.
Some compressors have a control to set the ratio anywhere between 1:1
(ie: no compression), and 20:1 (which would be regarded as a "brick wall
limiter"). In the mc2 the "Slope" or "Compression Ratio" is variable from 1:1
(ie: no compression) to 10:1. Slopes around 3:1 are gentle for vocals while
higher slopes are hard for drums and guitars. However that's not all there is
to it.
Variable Ratio
In the Joemeek optical compressor the compression 'threshold' is not
clearly defined and the compression ratio varies with the amount of
compression applied. Suppose the 'Slope' control is set to 5:1. For signals
only just exceeding threshold, the ratio is little more than 1:1. As the
compressor is driven harder, the ratio rises to 5:1, at least up to a point. It is
a feature of the Joemeek compressor that the compression ratio actually
reduces again during large transients and, adjusted correctly, this helps to
retain brightness that is often lost with other types of compressor. This is
why vintage compressors often sound more lively than their modern
counterparts.
Controls
'COMPRESS' sets the level of signal (the "Threshold") above which the
signal starts to be compressed. Turning the compression control clockwise
lowers the compression threshold, and drives the compressor harder.
'SLOPE' sets the average compression ratio applied to signals above
threshold. Lower settings (anti-clockwise) have less effect. Turning the
control clockwise increases the ratio and makes the effects of
compression more dramatic. At maximum (10:1) the Joemeek compressor
effectively becomes a limiter.
GR Meter
The LED GR Meter provides an accurate reading of gain reduction in dB, at
any given moment.
GR Hold
A problem with all compressors is that when the signal level falls below the
compression threshold, the gain rises to that set by the 'MAKE UP GAIN'
control. The result is that during gaps in the music, any background noise
will be amplified, and may become noticeable and even downright
annoying! This could be counteracted by using a noise gate or expander
gate but such devices introduce their own problems. The mc2's 'GR HOLD'
control works by freezing gain reduction at the level it was at just before the
signal dropped below the compression threshold. In this way there is no
overall increase in gain and the noise floor is preserved.
The adjacent 'ON' switch enables this feature and the LED lights when
active. This LED also changes color to indicate the status of the GR Hold.
Green means a usable signal is present and the compressor is responding
to the program material. Red means that the input signal has fallen below
the selected threshold and the gain reduction is now frozen at its most
recent level.
Stereo Width
This control allows the width of the stereo image to be modified, from
mono, to normal stereo, to extra-wide stereo.
Wide stereo gives the impression of a bigger sound stage and a greater
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'ATTACK' sets how quickly the compressor reacts to peaks above
threshold. Turn this control anticlockwise for a quick response. Slower
(clockwise) allows the fast leading edge of percussive sounds to pass
uncompressed for a moment, before the compressor reacts to control the
gain. This example of "changing the envelope" of a sound exaggerates the
percussive nature of drums and other instruments. Settings around mid-
position are used where the compression needs to be less obvious. Vocals
for example, require Attack times around 10msec for natural sounding
results. Faster attack times (anti-clockwise) in conjunction with large
amounts of compression, result in extreme "pumping" effects.
'RELEASE' sets how long the compressor goes on squashing the sound
for, once the signal has dropped below threshold. If it stopped instantly
there would be very noticeable modulation or "pumping" of the sound. So
we may want it to stop compressing less abruptly and that is what the
Release control is for. Generally, the longer the Release time, the less
obvious is the compression. Of course some "pumping" might actually be
desirable as a special effect and that is another way in which the envelope
of a sound can be modified. The mc2 Release is variable from 100mS up to
3 seconds giving a wide variety of effects.
'MAKE UP GAIN' sets a static amount of amplification, to restore the level
of the signal after compression. Correctly adjusted, there will be no change
in perceived volume as the 'COMP' in/out switch is operated.
How the compressor behaves actually changes with program content and
volume. So experiment with the controls with different kinds of material to
discover the range and depth of effects that can be achieved. The 'COMP'
in/out switch allows comparison between compressed and uncompressed
sound (blue LED lights when active).
sense of space and depth to a mix. Depending on the mix, it may also
create a sense of improved clarity. The "Mid and Side" technique
employed widens stereo without the dreaded "hole in the middle" effect (ie:
loss of center or bass components). Stereo widened in this way also
remains mono compatible.
The 'ON' switch allows comparison between processed and unprocessed
sound (LED lights when the 'STEREO WIDTH' control is active).
Outputs
CONNECTORS
Left and Right outputs are provided on TRS jacks. The adjacent switch
selects the output operating level to either +4dBu (suits most professional
studio equipment) or -10dBv (suits semi-pro or hi-fi equipment). Check
with the handbook for whatever you are feeding, to find out which level is
required.
The jack outputs are balanced and wired as follows:
Tip: + (hot)
Ring: - (cold)
Sleeve: ground
Balanced or Unbalanced
To run the ¼" jack outputs unbalanced, just plug in mono jack plugs. This
increases the gain of the "+" signal by 6dB, so there is no drop in level
compared with balanced gear.
All outputs on all NextGen Joemeek products are properly balanced, which
is to say there is a signal on both pins! In this way the maximum possible
common-mode rejection of interference, can be achieved at the receiving
end.
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