200e

oh crap, that formatting makes no sense (thanks Y!G)

On Mon, Apr 28, 2008 at 5:36 PM, ezra.buchla <ezra.buchla@gmail.com> wrote:

>   in case anyone is still interested in this rather tangential topic,
> here's some more OL action that went down... the short answer is no, the
> 210e doesn't perform phase reversal...
>
> > Re: 210e -- audio signal phase reversal?
> ///
> > doesn't produce delay, which is the essential component of phasers,
> etc.
>
> you're thinking of flanging. phasing is different because it has
> arbitrary notch and peak positions, and a small number of them, too.
> it's typically done with chains of all pass filters each one inverting
> the phase above some sperarate frequency so the center frequency of each
> stage sets a notch or peak F when recombined with the original signal.
> then it's sort of normal to sweep all the F's up and down together. I
> always wondered why no one moved each one around as they saw fit, but
> probably because it's hard to think of something nicer.. the stages are
> cool looking and I never learned how to analyse them formally, but the
> idea is that you feed the signal to both the inverting and non inverting
> inputs on an opamp, but stick a cap before of the - and a resistor
> before the +. the cap blocks DC so that all goes to the + and come out
> uninverted. as you go up in frequency more and more signal goes through
> the cap.. I think the CF is set by the RC time constant. then you VC the
> C or the R. I forget the curve the phase shift follows as F goes up..
> and as to why it shifts at all instead of dissapearing at the CF it has
> some thing to do with the impedance (voltage-current lead-lag), but i
> never got that far.. unsatisfactory I know yah but each APF is like a
> kinky little delay line, with feedback and feedforward. in a digital
> implementation this is quite literal; in analog i guess the caps and
> opamps provide inverted and uninverted history of some sort, but the
> whole process of course seems more opaque to me.
>
> the point is that you have to have SOME propagation through time to do
> filtering or phase transformation. it seemed that the original poster of
> this now somewhat baroque thread was hoping to find a short kinky delay
> somewhere in the 200e, that could be exploited for weird filtering
> effects. alas, no...
>
> AND another thing I don't understand this:
>
>
> > phase delay = p = 2/freq * arctan( (1-a)/(1+a) *tan(freq/2) ),
>
> doesn't that make the phase shift totally frequency dependent? or is
> there something about it that keeps it flat at low enough F's? I tried
> plotting it out, but couldn't really see what was what. can this be made
> flatter and flatter by adding terms in some known way? I'd like a good
> way of making fixed phase shifts. the only digital method I knew of was
> a hilbert FIR (only 90 degrees) that was pretty long (but maybe bacause
> it was really flat?). I bet lumpy stuff could be just as useful..
> yeah there's some phase distortion w/ that algorithm. it is sensitive to
> frequency (the lower the better) and the desired delay (the closer to a
> multiple of 1 sample the better), but at low frequencies it's quite
> flat. at the nyquist frequency everything converges to an integer
> multiple of the sampling period. oversampling helps.
>
> the thing to plot would be delay ("p") against frequency for a given
> parameter value ("a").
>
> i personally think the phase distortion is kinda nice when using this as
> a chorus or karplus-strong component. it's not exactly easy to hear...
>
> -eb
>
> --- In 200e@yahoogroups.com <200e%40yahoogroups.com>, "ezra buchla"
> <ezra.buchla@...> wrote:
> >
> > yeah, quadrature introduces a 90deg phase shift in an envelope.
> nothing to
> > do w/ audio.
> >
> > btw, it's pretty easy to make a digital APF with almost-linear
> arbitrary
> > phase response. combine a 1sample feedforward and 1sample feedback
> loop:
> >
> > y = a*x + x_last - a*y_last
> >
> > phase delay = p = 2/freq * arctan( (1-a)/(1+a) *tan(freq/2) ),
> >
> > so a = sin((1-p) * freq/2) / sin((1+p) * freq / 2))
> > , so for freq small relative to sample rate, a = approx. (1-p)/(1+p)
> >
> > but all this doesn't have much to do with the 200e. experiments with
> digital
> > filter architectures are probably best carried out on a computer.
> >
> > -eb
> >
> >
> > On Mon, Apr 28, 2008 at 12:11 PM, nicholas_kent zaum@... wrote:
> >
> > > Doesn't make much sense to me (But I don't own any modules). The
> 227e
> > > is a quad channel device. In general no one defaults audio as far as
> I
> > > know to 90 degree phase shifts to do quad. All you will wind up with
> > > is more potential of cancellation in an acoustic space. And 90
> > > degrees for that matter probably requires a pair of allpass filters
> to
> > > achieve. It's not something you can get without filters as far as I
> > > know compared to just inverting the polatity for 180 degrees (though
> > > filters could do that too).
> > >
> > > My guess is people are thinking along these lines because if you are
> > > mixing quad audio you might very well want to hit your VCAs with 90
> > > degree quadrature of a *control voltage* in order to do "circular"
> pan
> > > effects. Or perhaps someone just wants to identify the speakers in
> > > numbers rather than ABCD if they represent a quad space
> > >
> > >
> > > --- In 200e@yahoogroups.com <200e%40yahoogroups.com> <200e%
> 40yahoogroups.com>, "mritenburg"
> > > mritenburg@ wrote:
> > > >
> > > > I might be wrong, but I have always assumed that on the 227e,
> positions
> > > > A, B, C, and D are 90 degrees out of phase from one another. So C
> is
> > > > 180 degrees out of phase from A and D is 180 degrees out of phase
> from
> > > > B.
> > > >
> > > > Matt
> > > >
> > > >
> > > >
> > > > --- In 200e@yahoogroups.com <200e%40yahoogroups.com> <200e%
> 40yahoogroups.com>, "Matt
> Carpenter"
> > > <matfhew.carpenfer@>
> > > > wrote:
> > > > >
> > > > > Hi all,
> > > > > I was just wondering if the 210e allows phase reversal of the
> audio
> > > > > signal or if phase reversal is possible via other means,
> specifically
> > > > > for the purposes of feedback/feedforward experimentation.
> > > > > Thanks!
> > > > > Matt
> > > > >
> > > >
> > >
> > >
> > >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
> [Non-text portions of this message have been removed]
>
>  
>


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