On Fri, 06 Nov 2009 17:19:29 -0700, Jim Thompson
wrote:

On Fri, 06 Nov 2009 19:03:53 -0500, "Michael A. Terrell"
wrote:


Jim Thompson wrote:

On Fri, 6 Nov 2009 20:53:53 -0000, "ian field"
wrote:

[snip]

Can't I just make a PLL lock on to the frequency and stay put after the note
has decayed, then measure the frequency with a digital frequency counter?


A PLL that doesn't drift once it loses reference ?:-)


yeah. A Pathetic Locked Loopy.

I suppose you _could_ put a sample and hold on the control voltage,
but my experience with _good_ PLL's is that it takes around 100
reference cycles to ensure accuracy, _before_ you could "coast".

I think it should really be done with a high speed counter to get
signal period.

---
Indeed, but it doesn't have to be all that fast.

For instance, if he wants to get the period of A7 (3520Hz) to +/- 0.1%
he'll need a clock 1000 times faster, or 3.52MHz.

Then, to get rid of the +/- 1 count error he'll need to double the clock
speed to 7.04 MHz.

Easy...

JF