FMdave's dashboard

thanks for putting back phase wrap! Yes aahh!

Hi thend. I believe the answer is you've built a narrow bandpass filter that essentially allows 1400Hz signals through... this means that when the sweep gets to 700Hz, you will not see much 700Hz signal on the output, but the 1400Hz (2nd Harmonic) will be enhanced... therefore you see a 2nd harmonic distortion rise at 700Hz, and another at 1400/3 Hz for the 3rd. – FMdave, on September 28, 2008 00:03

inductor+capacitor in paralel – thend, on September 24, 2008 16:54

The distortions displays of the beta version work well but it's the same probleme for me.

For exemple, i have measured with an impedance wiring a inductor+capacitor in serie (resonant circuit) and I have this:



With the harmonique distortion display:



And in percentage:



The problem is, i'm pretty sure they have no resonnances below 1400Hz, and the distortion is a multiple of 1400Hz...

Why the distortions displays show me a distortion below 1400hz?

Thanks for putting the HD dB scale back in!! :) ... very useful (at least to me).

I've noted that when either HD scale is selected, the user is allowed to retain or select options in the Multiple Selection drop down...
which gives unexpected (and likely confusing) results, at least until one figures out that the "multiple selection" is actually combining single measurement harmonic curves... :) I can't think of a reason that such a combined HD plot would be useful for anyone ... as opposed to selecting actual multiple -measurements- and them combining -those- values.

Also noted that the HD % scale is selected, the option to change Smoothing is unavailable (grayed out)... whatever amount of smoothing was selected before choosing the HM % scale is what you get. Still can be changed, just not conveniently.

Never mind about my comparison (% vs dB) scale concern...
Below ~100Hz there was not enough signal from the MacBook
speaker to form a useful harmonic distortion value... i.e., was seeing
solely the "N" portion of "THD +N" :P

That said, I'd still hope to see the distortion products shown as dB relative
to the fundamental, even if as a selectable option. Thanks, -dave

Sure :)

http://www.jblpro.com/pub/technote/tn...

There are certainly other examples (including from JBL) that show
specific distortion artifacts in %, such as when attempting to
illuminate/highlight improvements that have been made in reducing 2nd
harmonic distortion in compression drivers, but those are specialized
case (and apparently are being used as marketing tools as opposed to
scientific investigations). Other vendors (when they are brave enough to
show these plots) tend to follow the dB scale usage, and the vertically
lifted harmonic plots.

BTW, the first run I ran of 3.1b2 using the harmonic distortion function
and comparing with 3.1b1 (converting from % to dB), simply using the
MacBook Pro internal speaker/mic, seemed to be not comparing well. I
didn't spend a lot of time to check this, but will try to this evening,
or tomorrow (% plot seemed to be a bit optimistic above a few hundred
Hz, iirc). I'll re-mail if I come up with a more concrete example.

Thanks and regards,

-dave

Dave,

Could you point me at some industry sources that list the decibel display as preferred display type?

The 3.1 beta is very mouldable right now and I want to be sure I get things like this sorted out sooner rather than later. I am a little bit in the dark when it comes to preferences for these more "exotic" graph types in fuzzmeasure. So, any pointers here would be appreciated.

3.1b2 appears to have dropped the dB harmonic distortion display.
I would call this a step backwards. Normal industry standards for plotting
loudspeaker driver distortion use a dB scale, also a "shifted" frequency
scale (as was the case with 3.1b1), and quite often a "raised by 20 or 30dB" amplitude shift for the harmonic components. An -option- to plot in % (vs dB)
might be use for some, but seems an odd choice as a default.