[sdiy] more pitch shifter thoughts

[Magnus Danielson]

From: Scott Gravenhorst <music.maker at gte.net>
Subject: Re: [sdiy] more pitch shifter thoughts
Date: Mon, 10 Jan 2005 15:58:08 -0700
Message-ID: <200501102358.j0ANu7V11198 at linux6.lan>

> >> My own circuit has adjustable damping for the loop filter and allows me to
> >> adjust it so that frequency changes are so immediate that I do not hear any
> >> over/undershoot or lag.  But then, my PLL has only a divide by 12 counter
> >> in the loop.
> >
> >That is a good move. However, by spending a little care will an octave of range
> >not be as much of a trouble. The trick is to make the loop-gain change occur
> >over a well damped case, so it's loosest end is more or less critically damped.
> >It is a bit of numerics but it is fairly simple to do.
> >
> >There is a bunch of different sources for the calculation, which one are you
> >using?
> 
> Oh just the simple one for calculating the capacitor value.  I don't have the
> details of what that mounted to.

Well, if you ever need to do it that way, you should now know the trick to use.

> >I've been doing multiplications beyond 2000 with no problems, but that was no
> >4046 in there. Infact, for some uses the 4046 is so darn bad, and especially
> >the charge-pump buissness has better reputation than it should have. Too many
> >use it blindly without understanding the issues. 
> 
> Like me!  Blindly used or not, I was extremely happy with the result. It does
> 5 octave jumps with little more than a chirp.  I drive it only with a VCO
> output that presents a signal as large as the 4046 rail to rail voltage. 
> I used Phase Comparator II to get the large lock range and prevent locking
> onto harmonics.

Well, it IS a good PLL chip for some uses, and it is a very neat little tool
that can be put into good use in many applications in and outside of audio.
Put it has its limits and I sure bumped into them when someone designed a PLL
for 155,52 MHz with it as the phase detector (at comfortable 8 kHz). The
charge-pump was doing just that, pumping here and there... so the clock became
jittery because of the 4046. For that application the 4046 was in way over its
head. A 74VLC00 or similar took over it's job and did so splendidly.

> >Let's say I'm not impressed
> >when seeing it in action in what proved to be a critical application, where as
> >using a much simpler setup locked and just kept going without headaching
> >trimings and problems.
> >
> >OUPS! Now I am 4046-bashin again!
> 
> Ah, well, probably my application wouldn't be considered "critical",

In the above case another designer took (unknowlingly) the 4046 out for a
tougher testdrive than intended, and then he already compesated for some of its
flaws.

> it only has to sound good, I don't care too much about problems that don't
> present themselves to my ear.

Like I said, for some applications it is great, just what the doctor ordered,
but for some it aint. I am all for using it for many, many synth applications,
it will be just right for the job for most of them. But for higher frequencies
and for ultra-low jitter, it should not be considered.

> The only reason I soldered it together is that I tested the design on
> solderless breadboard and it worked surprisingly well, far better
> than I'd hoped.

Good for you! I had also great fun playing around with the 4046 and a divider
chain my first time. It was hard to verify it really did the x128 that I asked
for, but it did oscillate nicely! ;O)

> Thanks for the info.  Again I get an education on this list.

All you have to do is to ask, you know that. Especially about PLLs, which is
one of my favorite areas. Also, we have others here who know about them (you
know who you are), so you should not be all alone.

Cheers,
Magnus