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TU B E M I C
CHAN N E L STR I P
input to output ratio, meaning no compression would be applied. Use lower settings for gentle compression and higher
settings for heavier compression or limiting.
6. Makeup Gain Control [-20 dB to +20 dB]
This control adjusts the gain post-compression and pre-limiter. Generally, this control is used to make up for the
amount of gain lost due to compression. This effectively increases lower-level portions of the signal so that they aren’t
‘lost in the mix’ and allows you to better judge what the compressor is doing when comparing the compressed verses
uncompressed signals.
One way to set this control is to simply look at the VU meter with the VU meter selection set to ‘G.R.’ (Gain Reduction)
mode and set the MAKUP GAIN control to the same value. For example, if the G.R. meter reads a maximum of -5
dB of gain reduction, you would set the MAKEUP GAIN control to 5 dB. A more precise method for setting the
MAKEUP GAIN is to adjust the control as you audition the compression. To do this, A/B the compressed signal with
the uncompressed signal using the COMP/LIM ENABLE button and set the MAKUP GAIN control so that both signal
levels match during song sections where the most compression is being applied.
7. Peak LED
If this LED lights, it indicates that the signal level from the compressor section is clipping the output stage of the 676
and the MAKEUP GAIN control should be reduced.
8. Contour Button
This button enables a high pass filter in the compressor’s detector circuit. This will gently roll-off low frequencies and
prevent them from triggering compression. Enable this button to minimize ‘pumping’ or ‘breathing’ artifacts which can
occur when attempting to apply heavier compression to signals with excessive energy in the lower-frequency region,
such as a bass guitar, bass synth, or kick drum. When enabled, this feature allows for faster attack times and higher
compression ratios with less artifacts.
9. Sidechain Enable Button
When this button is engaged, the signal will pass through the SIDECHAIN INSERT jack on the rear panel. Using the
SIDECHAIN INSERT jack allows you to insert an external processor for altering the signal feeding the compressor’s
detection circuit. This can be used for frequency-weighted compression applications, such as de-essing, or for other
creative sidechain compression techniques, see
‘Sidechain Application’ on page 21
for more information. Note
that when nothing is connected to the SIDECHAIN connector, enabling this button will have no effect on the audio.
10. Attack Control [400 dB/msec - 1 dB/msec]
This control adjusts the amount of time it takes the compressor to react and begin compressing the signal. 400
dB/msec is the fastest attack setting. Theoretically, this means that it would take the compressor 1 millisecond to
compress the signal by 400 dB. So when applying 10 dB of compression with an attack time setting of 400 dB/
msec, the attack time would be 25 microseconds (400/10 = 40, 1 msec/40 = .025 milliseconds, which converts to 25
microseconds). Conversely, 1 dB/msec is the slowest attack setting. So if we use the previous example and apply 10 dB
of compression using the slowest attack setting of 1 dB/msec, the attack time would be 10 milliseconds (1/10 = 0.1, 1
msec/0.1 = 10 milliseconds).
11. Auto Button
This button toggles the compressor’s AUTO function on and off. When this button is disengaged, the compressor
will react based on the ATTACK and RELEASE control settings. When this button is engaged, the compressor will
automatically adjust the attack and release characteristics based on the incoming program signal and the ATTACK and
RELEASE control settings will be ignored.