As shown by the equations in Pipelined CIC Decimatorand Register Growth in CIC Interpolator, the gain of a CIC filter is a function of all the key design parameters. When the output width is equal to the maximum register width, the core outputs the full precision result and the magnitude of the core output reflects the filter gain. When the output width is set to less than the maximum register width, the output is truncated with a corresponding reduction in gain.
When the core is configured to have a programmable rate change, there is a corresponding change in gain as the filter rate is changed. When the output is specified to full precision, the change in gain is apparent in the core output magnitude as the rate is changed. When the output is truncated, the core shifts the internal result, given the Bmax for the current rate change, to fully occupy the output bits.