[PD] controlled vibrato

[Libero Mureddu]

Hi list,
continuing my experiments with vibrato and glissandos, I ended up in this:
I´d like to have a vibrato around a certain frequency, in which I can decide
to go upwards of a certain amount (ie one octave) but downwards a different
one (ie. one 5th), and the possibility to control those parameters.
In other words, I´d like to have a modulating wave that has a certain
amplitude when goes up, and a different one when goes down.
I do not want to use a sine wave with an offset, because I would lose the
regularity of the 0 amplitude point.
A friend suggested me to use two sine waves with same frequency but
different amps and "half rectify" them, in the first excluding the negative
values and in the second the positives, in order to create this pseudo-sine
wave.
See half-wave rectification here:
http://en.wikipedia.org/wiki/Rectifier
I made a simulation of the kind of wave I´m thinking, see attached jpg file.
But, once again, I don´t know how to do that in pd, and I don´t know if
there are better ways to do that.
Hope my explanation is enough clear!
thanks

libero
-- 
Libero Mureddu
Vanha Viertotie, 21 as 417
00350 Helsinki
Finland
http://webusers.siba.fi/~limuredd/
http://www.myspace.com/liberomureddu
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