[sdiy] Clock-controlled filters?

cheater cheater cheater00 at gmail.com
Fri Oct 19 21:11:02 CEST 2012


Hi guys,

Tom, thanks for the info on the PLL. I hadn't realized that's the way
you multiply frequencies with a PLL. At second though, I might
actually need that.

Ullrich, thanks for the tips on the parts, it does seem like a fairly
simple project. Also thanks Pete.

Richard, yeah, I did recollect that they used switched-cap filters but
I decided to ask because you never know. I don't want to use a
fixed-freq DAC for the exact reason that it's fixed frequency. Instead
I would like to output this from a variably-clocked DAC. The idea
which I'm playing with is to build a sampler which does not use
digital interpolation. I think it might be possible to build a FM'able
clock for some sort of uC that can accept variable clock rate. There
are many arm-based offerings that can do that. For the clock, perhaps
one of the many pulse-train-output products out there, similar to what
David was looking at but with higher frequency interval (it'd still
need to track about 10 octaves). Horowitz-Hill lists some things (some
have since become obsolete but got replaced with newer ones). I guess
I'd just output the waveform via an R-2R DAC and buffer and put it
through the imaging filter. In this case the interpolation is purely
analog (i.e. the imaging filter). I do believe the original e-mu
sampler used a variable rate DAC approach, but I wonder how they did
the imaging filter. In specific I wonder if it was a switched-cap or a
VCF.

Cheers,
D.

On Fri, Oct 19, 2012 at 2:03 PM, Pete Hartman <pete.hartman at gmail.com> wrote:
> The Blacet Time Machine uses a pair of LTC1063's as clocked anti-aliasing
> filters for the MN3005 BBD, so that's another chip you could use.
>
>
> On Fri, Oct 19, 2012 at 5:45 AM, Ullrich Peter <Peter.Ullrich at kapsch.net>
> wrote:
>>
>> Hi!
>>
>> I designed a tracking filter for a measurement circuit for balancing high
>> speed spindels of RC model aeroplane turbines.
>>
>> The clock to which the filter frequency had to be adjusted/regulated was
>> the spindle rotation frequency (generated with a reflectocopler that made
>> nice pulses due to black markings on the silver spindle). The used maxim
>> filter chip needed 100 times the frequency for proper work so I added a 4046
>> PLL chip.
>> The result was a  bandpass filter that moved with the center frequency.
>>
>> I think this design could be adapted for audio usage by recalculation.
>> I used a MAX267 switched capacitor filter chip for that.
>> http://www.maximintegrated.com/datasheet/index.mvp/id/1186
>>
>> Ciao
>> Peter
>>
>> http://www.ullrich.at.tt
>>
>>
>> -----Ursprüngliche Nachricht-----
>> Von: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] Im Auftrag von cheater cheater
>> Gesendet: Freitag, 19. Oktober 2012 11:03
>> An: synth-diy
>> Betreff: [sdiy] Clock-controlled filters?
>>
>> Hi guys,
>> are there filter designs, not necessarily resonant, which tune to pulse
>> train input?
>> Chips are good too - although being able to make it discrete if/when the
>> part becomes obsolete would be a huge plus.
>>
>> Cheers,
>> D.
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