TYPE: CHOP
TITLE: Pass Filter CHOP

This CHOP filters audio input using one of four different filter types. Incoming
channels are broken into chunks that overlap in time.

The second input is the Filter Animation Channels, which allows the filter
parameters to be changed over the CHOP's interval. See the Band EQ CHOP
popup help, or the section in the Common Options of CHOPs called Filter
Animation Channels Input.

This CHOP may be time sliced to filter audio in realtime.

See the Pass Filter CHOP section in the Houdini manual for explanation of
filter terminology.

Parameters:
Filter
    Filter            - Filter type:
	Low Pass Filter  - All frequencies below the High Cutoff are passed
			   through the filter (the "pass band").
	High Pass Filter - All frequencies above the Low Cutoff are passed
			   through.
	Band Pass Filter - All frequencies between the Low and High Cutoff are
			   passed through.
	Band Stop Filter - All frequencies above the High Cutoff and below the
			   Low Cutoff are passed though.
    Low Cutoff        - The frequency (in Hertz) of the lower cutoff.
			This value is not used by a low pass filter.
    High Cutoff       - The frequency (in Hertz) of the upper cutoff.
			This value is not used by a high pass filter.
    Pass Gain (dB)    - The gain of passed frequencies, specified in dB
			(decibels). Every increase of 20dB corresponds to
			a 10-times power increase.
    Rolloff Factor    - How the filter drops off at the cutoff frequencies.
			Low values (less than one) produce more gradual
			rolloff, and higher values produce sharper filters.
    Also Filter Phase - Normally, the magnitude of the signal is filtered.
			You can optionally filter the phase of the signal.
Digital
    Filter Chunk  - This parameter allows you to select the chunk size,
		    to balance the demands of animating filter parameters
		    with the quality of sound.
    Chunk Overlap - How much of the current chunk is overlapped and
		    blended with the previous chunk.  From zero (no
		    overlap and blending) to .95 (95% overlapped). Keep
		    between .05 to .3.  Values too close to zero will
		    not entirely remove the discontinuity.
    Chunk Discard - The chunk to throw away. Since the middle section
		    is most accurate, the end sections are discarded.
		    From zero (don't discard anything) to .95 (keep only
		    the middle 5%).  Normally discard between .05 and .2.

Local Variables
    I   - current evaluation index.
    N   - current chunk being filtered.
    C   - current channel being filtered.
    NC  - total number of channels.

See also: Audio In(audioin), Band EQ(band), Filter
