FMdave's dashboard

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If one were to always plan ahead and never change the reference measurement, then that might be one solution. I did try selecting an exported FRD as a mic cal file, after the fact (not expecting it to work...
it didn't, in fact 3.2b5 "quit unexpectedly" when attempting a 2nd
measurement -after- importing the ref cal file [macos 10.6.1/32bit]).

Yes. The yellow, 15deg plot was what I started with... itself a multi-select
difference plot (vs a reference 0deg measurement) exported as a graphic. The 30 and 45deg series were similarly created, the trace/color selected, cut and pasted into the 15deg plot... admittedly, a bone-headed approach, but that is the information I wanted to display. Doing the same thing at 5deg intervals
would be tedious, as would exporting FRD's, cutting and pasting into another plotting program.

I'd like to second the request for what is essentially selecting -one- of many measurements in a FM file as a reference amplitude curve which can be
used to normalize a family of curves (multi-subtract? or multi-add).

I've attached an example plot that was manually edited in a graphics program to perform this function (individual differences vs. the reference curve plotted in FM, then graphically cut and added to a base plot ... not fun or pretty). I've not been able to successfully apply any of the combination or operation
functions (current or beta) to achieve this. Could be I'm doing something wrong.



-dave (3.2b5 user)

Re: saving presets ... all for it, in regard to SPL calibrations, it would indeed be quite welcome and useful to have some persistence between sessions (understanding that which mic, pre-amp level settings, etc... would be useful to record to help ensure the preset is valid). The user should be able to make the decision about whether the calibration is valid (a bypass-able warning would be ok).

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

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

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.