Chirp generator

[Jeremy Brookes]

>>I want to build a stomp box that would produce an attacking chirp sound
>>when activated.  What is the easiest route?  I tried attaching a
>>simple attack/release envelope to a trigger pulse but the sound was a
>>weak blip instead of a harsh chirp.  Has anybody built anything like
>>this?  Any advice would be appreciated.

>Well, a chirp is a signal whose frequency is proportional with time.
>So I would go for a saw-lfo(s) that controls amplitude and frequency of
>a (linear) vco.

You might have a problem with the LFO starting a new cycle in mid-chirp. 
You'd have to trigger the LFO from the AD envelope. Alternatively, you 
could sweep the oscillator with the AD.