In dual mono mode, the Fairchild 670 operates as two separate monophonic
compressors with independent control of the left and right channel signals.
There is no interaction between the two compressors.

Dual Lat/Vert

In dual lateral/vertical mode the Fairchild 670 operates as two monophonic
compressors with independent control of the middle and side components of
the two input signals. The input signals are processed by the sum/difference
(mid/side) matrix before and after the compressors, but there is no interaction
between the two compressors.

Stereo

Left/Right

In this mode, the Fairchild 670 operates as a typical stereo dynamics proces-
sor. The left input is fed to the one compressor, and the right input is fed to the
other. The dynamics control signal sidechain of the two compressors are
linked so that they both compress the same amount at any instant, preventing
transients which appear on only one channel from shifting the stereo imaging
of the output.

Any transient above the threshold (on either channel) will cause both channels
to compress, and the amount of compression will be similar to the amount of
compression for a transient which appears on both channels at the same time.

Additionally, the attack and release times for the two compressors will be the
same, and attack and release behavior will be the average of the settings for
the two channels. Mono transients will have an effective attack time of about
one half the attack time for transients on only one of the two channels.

Table 14. Fairchild Operating Modes

AGC Switch Setting

Sidechain Link Setting

Operating Mode

Left Right

Unlinked

Dual Mono

Lat Vert

Unlinked

Dual Lateral/Vertical

Left Right

Linked

Stereo Left/Right

Lat Vert

Linked

Stereo Lateral/Vertical