[sdiy] BBD Chips

[harrybissell]

Hiya Scott...

with two parallel delays (and no straight signal) through zero flanging
is no problem... in fact the original tape flanging had a LOT of delay
(it was not real-time).

The trick is that most people (me too) like their flanging in real time...and
a 17ms straight out delay is pretty obviously 'late'. I used to use 30ms
fixed delay to time align my guitar and guitar synth... which made it
impossible for me
to listen to my playing (the delay caused a tempo-reducing feedback).  It was
OK for the
bass player and singer, who followed by listening and adjusting time (like
phase lock) but
drove the drummer crazy (he was syncronizing visually... a good trait in a
drummer who can
eliminate the 1ms/foot time delay of sound in air)...  The drummer KNEW for
sure that my
hand was way early from the sound.

Depending on the amount of modulation you want from either side of "zero" you
can do with
as little as 2ms of fixed delay, and be real careful in modulation to just
'kiss' the zero point and back away in the same direction.

H^)  harry of green llamas

Scott Stites wrote:

> Hi Harry,
>
> I think that's it!  I remember now, to that I had gotten a sort of
> through-zero flanging with two PT2399 chips, but it was a little rough
> (minimum delay is rated at something like 30 ms, though I think I may have
> been squeezing 17 ms out of it).  Makes it hard to control without getting
> into the 'doubling range', plus at the time I wasn't sweeping with the best
> kind of wave (for flanging).
>
> I remember mentioning I didn't think it was 'real' flanging as there was no
> way to feedback in the same 'time zone', but IIRC, you pointed out that
> feedback wasn't strictly required for flanging.
>
> It was green - did that really happen?  =0)
>
> Take care,
> Scott
>
> ----- Original Message -----
> From: "Harry Bissell Jr" <harrybissell at prodigy.net>
> To: "Scott Stites" <scottnoanh at peoplepc.com>; <synth-diy at dropmix.xs4all.nl>
> Sent: Tuesday, July 22, 2003 3:58 PM
> Subject: Re: Re: [sdiy] BBD Chips
>
> > Yeah so it was a black and white llama then ???? ;^P
> >
> > You could do the through zero with BBDs.... the
> > problem will be you want to keep the fixed delay
> > short.... and vary the other delay.  So a long BBD has
> > to be clocked at a very high rate.... or you would
> > possibly need unequal length BBDs that would have
> > different attenuation and noise levels.
> >
> > I did the through zero trick with two DeltaLab
> > "Effectrons" and it works great. You will never need
> > a delay longer than 16ms.... with probably a 4ms delay
> > being ideal.  This might be the point you remembered
> > ???
> >
> > H^) harry
> >
> >
> > --- Scott Stites <scottnoanh at peoplepc.com> wrote:
> > > 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)
> > > >
> > >
> > > ________________________________________________
> > > PeoplePC:  It's for people. And it's just smart.
> > > http://www.peoplepc.com
> >
> >