Extracts bass from the source signal using a linear phase low-pass filter and sends it to the LFE channel.
Features:

• fast fir processing
• adjustable filter shapes
• delay control
• mono, stereo, 3.0, 4.0, 5.0 input support

foobar2000.org/components/view/foo_dsp_subwoofer
HA Forum Topic

Linear phase is a property of a filter, where the phase response of the filter is a linear function of frequency. The result is that all frequency components of the input signal are shifted in time (usually delayed) by the same constant amount (the slope of the linear function), which is referred to as the group delay. And consequently, there is no phase distortion due to the time delay of frequencies relative to one another.

~ en.wikipedia.org/wiki/Linear_phase