[sdiy] Frequency counter

[John Loffink]

Paul's comments regarding traditional frequency counters are correct.  They
are optimized for radio frequency work and use the simple gate/count
technique for frequency counting, which is too slow for audio.  I had an HP
5314A Universal counter with 0.1 Hz accuracy, but it took 10 seconds between
gates for the reading to update.

Modern DMMs are somewhat better for audio range work, though check the
accuracy before buying.  You want better than 1% accuracy when tuning VCOs,
for instance, and that's what most brands of DMM provide for accuracy.

The Extech line of DMMs have frequency resolution surpassing the name brands
such as Fluke.  Model MT310 has 0.1% accuracy and 0.1 milliHertz resolution,
for instance, and that's in the sub $100 range of DMM.  The MM560 has +/-
0.008% accuracy and 0.1 millHertz resolution.  Some of their units cover the
LFO range, and some do not.  Check the specs at their web site.

http://www.extech.com/

John Loffink
The Microtonal Synthesis Web Site
http://www.microtonal-synthesis.com
The Wavemakers Synthesizer Web Site
http://www.wavemakers-synth.com


> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl [mailto:owner-synth-
> 
> 
> From: "Mikael Mørup" > Are the ones that are build into the better digital
> handheld
> > Volt/Amp/Ohm meters good enough for synth DIY work ?  Do
> > they have the required precision ? do they cover the low
> > LFO range ?
> 
> A problem with 'common' freq meters, is that they are intended for radio
> frequency work.
> And they usually total cycles over 1 second.
> So that isn't too useful for LFO examination!
> 
> The frequency meter you wnt for LFO examination is one that has a "period"
> function, that
> is to say, it has a mode where you can check the time taken for a cycle to
> run, then
> you just invert this to get the frequency.
> 
> I've only got an RF model, so I use the scope to check the LFO rate.
> Fortunately, the lower the LFO gets, the easier it is to tell the freq,
> just
> by
> counting seconds! you don't often need any precision in this application.
> 
> If you want to calibrate your VCO with a freq meter, a RF meter won't give
> enough
> accuracy (unless it has an extened time feature, where it counts a lot
> longer than a second),
> and a DMM definitely won't do. I believe most DMM freq counters work like
> a
> tachometer, they have a monostable pulse generator that spits out a little
> charge for each
> pulse & then averages the current (more pulses = higher freq). Not
> precision.
> 
> For calibrating purposes, zero beating with a digital synth or organ might
> be the easiest.
> paul perry Melbourne Australia
>