t* spectral slope correction (simple simulation of attenuation)

*call	filter
bslope	40	tstar	2.5

#	to reverse the band-slope effect, use:

*call	filter
bslope	40	tstar	-2.5
polygon	bp
5	8	60	100

#	here, a band-pass filter is added to restrict the frequency band
#	and avoid boosting high-frequency noise