The Equaliser Preferences alter the way REW carries out its EQ filter calculations.
The Default Equaliser specifies the equaliser that will be used for new measurements. The equaliser used for an existing measurement can be changed via the EQ panel.
When matching filter characteristics to resonances the optimiser does not limit filter attenuation, this allows it to correctly determine the required Q for each filter. Once a good match has been achieved, the attenuations are limited to the maximum that the EQ filters allow then the attenuation (but not Q) of each filter is re-optimised accordingly. If the Allow Doubled Filters option is selected the optimiser will allocate an additional filter for peaks that remain above the target level when optimisation has completed. The second filter is chosen according to the following criteria:
As an example, consider a peak at 100Hz that requires a filter with 21dB attenuation to bring the response down to the target, but our filters have a maximum attenuation of 15dB. A further 6dB of attenuation is required. If there is an unused filter then it will be assigned to provide this extra 6dB of attenuation at 100Hz. If not, but there is a filter being used to correct another peak (let's say at 45Hz) that has a smaller impact on the overall response, it will be re-assigned to make up the shortfall on the large peak.
If Drop Filters if Gain is Small is selected any Automatic filters which have gain of magnitude less than half the flatness target at the end of the optimisation process will be freed up (their Type will be set to "None")
The default values to use for Speaker Type, Cutoff, Crossover slope, LF Slope and LF Cutoff are specified here, these will be used for each new measurement. The LF Cutoff and LF Slope define the lower extension limit for subwoofer's or full range speakers and how quickly that extension rolls off.