[sdiy] BBD Chips

[Scott Stites]

Thanks guys!  (Mental Note:  Never post before morning coffee).  Filter before
mix.  Sigh.

But on first glance of Roman's idea for through-zero flanging something twanged
in my brain about it being problematic when implementing with BBD's.  It seems to
be from some previous discussion on this list or maybe it was off-line.  Or
perhaps I dreamed it - Harry Bissell on a green llama saying "#%s#ssshhhThou
zshalt not tHroew w sszero with bBd..D..Sd..zzst" (bolt upright in bed).  Nah,
that wasn't it.  I don't dream in color =0).

Somewhere on the net I picked up the doc "flanger.pdf" that is a copy of a 1984
ETI article detailing the construction of a chorus/flanger unit using the
MN3207/MN3102.  I borrowed the part for the transistor current sink from that for
the flanging (it's got a linear sink also for the chorus part).  

Cheers,
Scott


On Tue, 22 Jul 2003 18:57:30 +0200, "Jaroslaw Ziembicki" wrote:

> 
> ----- Original Message -----
> From: "Scott Stites" <scottnoanh at peoplepc.com>
> To: <synth-diy at dropmix.xs4all.nl>
> Sent: Tuesday, July 22, 2003 5:51 PM
> Subject: Re: Re: [sdiy] BBD Chips
> > But wait - don't ensemble choruses by nature have the BBD clocks
> 'crossing'
> > themselves in the frequency domain?  Now I'm confused.....
> 
> Yes, the clocks are independent, but there's no danger that any new
> frequencies in the
> audio range would arise.
> It's due to a fact that the output signals of all BBD's are mixed together
> in a *linear*
> summing circuit. That means, no additional sums/differences of output
> frequencies can
> arise. The signal after mixing is a sum of "useful" low frequencies, and
> high frequencies
> which result from the sampling. After low-pass filtering, only the "good"
> low frequencies
> will be left at the output.
> Of course the input signal or signals must be well low-pass filtered before
> passing in the
> BBD (or BBDs) in order to cut off any frequency that is above the half of
> the BBD
> clock frequency. It's the well-known Shannon theorem - also called the
> Kotielnikov
> theorem in some countries ;o)
> 

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