[sdiy] Tap Tempo LFO

[Jerry Gray-Eskue]

<<So I believe we agree - with a simple external oscillator and minimal
control it would be possible to create a clock for a BBD using a cheap
MCU.>>

I would add that for pure delay and echo effects, i.e. max clock around
51,200 Hz - 20 ms delay and longer with a 1024 stage device a cheap
controller alone may suffice.

- Jerry


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of Eric Brombaugh
Sent: Wednesday, December 09, 2009 9:29 AM
To: Antti Huovilainen
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Tap Tempo LFO



On Dec 9, 2009, at 5:18 AM, Antti Huovilainen wrote:

> On Tue, 8 Dec 2009, Eric Brombaugh wrote:
>
>> Using a general-purpose MCU to create a clock for a BBD is probably out
of the question for most garden-variety processors. While a lot of them have
divider-based timing generators built-in, the high-frequency resolution is
probably not adequate to support decent timing & frequency control at the
rates needed to clock a BBD.
>
> Here I disagree. A simple VCO is not that hard to do if you stick to V/Hz
and disregard linearity. A PLL would also be dead simple to do, too.
>
> With the VCO you need to build a calibration table and/or adjust the
frequency on the fly, but that's hardly rocket science.

Perhaps I need to defend the statement above with a little more detail:

* 'general purpose MCU' means an inexpensive processor with a normal
complement of peripherals like low-res ADCs, timers, GPIO, etc. Think a PIC
or AVR.

* I thought the OP was talking about creating a BBD clock source without
using any other external components - that was my assumption in this first
paragraph. Further on I discussed the possibility of adding an external PLL
or programmable oscillator.

So I believe we agree - with a simple external oscillator and minimal
control it would be possible to create a clock for a BBD using a cheap MCU.

Eric
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