This function makes it possible to switch the feed of the sidechain alternatively behind (feedback) or in front (feed forward) of the actual compressor section. It has an enormous effect on the character of the compressor: While processing in feedback mode is smooth and even, switching into feed forward mode will result in a clearly stronger and harder kind of compression.
From the technical point of view this function mainly influences the characteristic curve of the ratio value. In feedback mode it goes up to a moderate ratio of 1:2.5. In contrast, the feed forward mode provides much higher values which also allow limiter settings and even negative ratios (i.e. loud signals will be reduced even more). Small changes in dynamics can generate a high amount of gain reduction.
The values of the attack controller also change noticeably in feed forward mode, as they are almost twice as high as the values shown on the scale.