Yorick routines defined in file filter.i

_	+++		cheby2	fil_cheby1		filter
	_cauer_parameter	F	+++	fil_cheby2	T	+++
B	+++		fft_good	fil_delay		to_db
	butter		fil_analyze	fil_make		to_phase
C	+++		fil_bessel	fil_normalize		+++
	cauer		fil_butter	fil_poly		+++
	cheby1		fil_cauer	fil_response		+++