[sdiy] Tap Tempo LFO

[David Moylan]

What about using a PLL to multiply the frequency?  Tap sets the total 
delay time and PLL multiples to desired HF clock frequency.  Since BBDs 
are usually powers of 2 in length a counter in the PLL feedback should 
do it.  You could also add a slew knob so you could tap a new frequency 
and have the PLL gently glide to it.

Dave

Tom Wiltshire wrote:
> Mike,
> 
> Thanks for the kind words.
> 
> There are two reasons why what you suggest isn't possible.
> 
> One is that the output sample rate simply isn't high enough. It's only 
> 19.5KHz, which rules out any frequency above almost 10K even in theory. 
> In practice, you wouldn't get much above 2 or 3KHz. The sort of output 
> rates you're talking about are 100's of KHz.
> 
> Secondly, the part of this that is 'tap tempo' is the LFO frequency, 
> e.g. the rate of change of some parameter. This is not the same as the 
> delay time being tap tempo. For this, you need to do a different sum 
> involving the clock rate of the delay and the length.
> 
> It's a damn pity that it isn't do-able though, because this is something 
> I've wondered about enough times myself. If you could get a uP to 
> generate a clock signal for a BBD directly, you be able to do tap-tempo 
> delays, flangers, chorus and the like, and you'd only need the uP and 
> the delay line. None of that messing about with clock chips or VCOs 
> driven by LFOs.
> 
> Still, BBDs suck, so it doesn't matter, right? ;)
> 
> T.
> 
> 
> On 8 Dec 2009, at 20:44, Mike Beauchamp wrote:
> 
>> Tom, First of all this is absolutely brilliant.
>>
>> Secondly, I'm wondering how easy it would be to reprogram it to have a
>> 1:4096 tap:clock ratio? (if that makes any sense).
>>
>> The reason I ask is that I'd really like to use this to add a
>> tap-tempo to an analog delay...
>>
>> The actual wave output could remain 1:1, just the clock output needs
>> to be 1:4096. Then I could use the wave output to drive an indicator
>> LED for example.
>>
>> -- 
>> Mike Beauchamp
>> mobile: +64 21 0 AS I BIKE (2742453)
>> home: +64 4 801 8304
>> work: +64 4 915 4068
>> http://mikebeauchamp.com
>> http://therevox.com
>>
>>
>> On Wed, Dec 9, 2009 at 12:40 AM, Tom Wiltshire <tom at electricdruid.net> 
>> wrote:
>>> Hi All,
>>>
>>> I've mentioned my Tap Tempo LFO project here before. The difference this
>>> time is that I've actually finished it!
>>>
>>> Details are online:
>>>
>>> http://www.electricdruid.com/index.php?page=projects.taplfo
>>>
>>> There are example circuit diagrams for a tap tempo LFO, tap tempo 
>>> sequencer
>>> clock, and tap tempo tremolo, plus, a datasheet, code, etc. Any 
>>> questions,
>>> please ask.
>>>
>>> If you're into PIC programming or know someone who is, you can get 
>>> code from
>>> the site. If not, I'll be trying to sort chips out soon, and if I can
>>> persuade Steve Daniels that this is a good idea, you might be able to 
>>> buy
>>> programmed chips from Small Bear. He did show some interest, but 
>>> we'll see
>>> whether it's really worth his while. I hope so.
>>>
>>> Thanks,
>>> Tom
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>>>
> 
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