blp - bandlimited pulse generator

blp output[b] amp[bvpn] incr1[bvpn] incr2[bvpn] n[bvpn] sum1[dpv] sum2[dpv] ;

blp generates a bandlimited pulse wave which contains n equal-amplitude
sinusoidal components starting at frequency f1 (specified by inc1) and 
spaced upwards by frequency f2 (specified by inc2) according to the closed
form formula:

    n-1
    ___
    \   sin( A + kB ) = sin( A + (n-1)B/2 )sin( nB/2 )csc( B/2 ) 
    /__

    k=0

where:	A = 2pi*f1*t, and
	B = 2pi*f2*t .

If f2 is equal to f1, then a harmonic spectrum will result, i.e., 
the first n harmonics of f1 will be present, all at equal amplitude.  
blp is useful to efficiently generate harmonic-rich waveforms that do not 
produce foldover as long as the value of n is less than 1 + (R/2 - f1)/f2
(where R is the sampling rate).

