[sdiy] Tap Tempo LFO/Clock

[Tom Wiltshire]

On 12 May 2009, at 13:44, Michael Zacherl. wrote:

> Hi Tom,
>
>>  I've added a "tap tempo" feature. This measures the time between  
>> two rising edges on one input pin and sets the LFO frequency based  
>> on the result.
>
> so it delivers a proper waveform tracking the frequency of the  
> input signal?

Yes, exactly.

>> It'll work with a momentary push button or a 0-5V pulse train, so  
>> it works as a sync-able LFO too.
>
> "Syncable" I understand as a feature that resets the oscillator in  
> the analogue world, which causes a "broken" wave cycle.
> But I suspect that's not what you're intending?

No, the original code had a synth-style "hard sync" input like you're  
talking about. The new code changes the frequency of the LFO to match  
the incoming pulses.

>> What applications do you see for a chip like this?
>> What features would you like to see on a chip like this?
>
> Multiples and fractions of the input frequency would be nice, IMHO.
> Going more crazy if the factor could be determined by a CV!  :-)

Ok, I'll bear that one in mind.

>> What could I get rid of from the original VCLFO?
>
> I'd keep the wave distort cv.
> The S&H feature isn't really important as long as your conceived  
> RND wave has a loooong cycle.

You mean that the random wave doesn't repeat? I used a 32-bit LFSR,  
so it generates over 500 million random bytes. So, no it doesn't  
repeat any time soon.

> I just noticed that I'm about to a get bit crazy: How about sort of  
> a loop? Which means you would need to store (?) the previous RND- 
> fragment somewhere.
> No idea by now how to control that, but if you just heard a nice  
> sequence from RND, push a trigger and it loops.
> Loop length could be determined by the "factor-CV" (see above).
> Something I wouldn't know how to do in pure analogue technology.

This would be possible. The "random" element is generated by an LFSR,  
so if you keep track of where you are in the sequence, you can repeat  
the sequence from that point. One of the Nord synths uses this idea  
for its "Synced noise" oscillator waveform.

> But I'm afraid you'd be running out of I/O on the PIC ...

That's what usually happens!

>     Just some thoughts - cheers, Michael.   :-)

Thanks Michael, exactly what I was looking for.

Regards,
Tom