Jean-Pierre Côté's dashboard

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?

You can send it to support@supermegaultragroovy.com and I can take a look at it.

Hi there, sorry was away till now.
I've zipped an exported filter, it's pretty small. Do you have an email address I can send to?

cheers

Hi, was looking for mic calibration info, I just downloaded FuzzMeasure and am evaluating, I realize that I can't use Mic Calibration and other useful features until I purchase, so I have a couple of questions.

I have a home studio in a basement with 2 recording booths. I can go out and buy calibration mics, but I was wondering after reading this thread if any of the existing mics I have might just do the job really well to begin with. Here are my list of options, I hope you don't mind giving me guidance:

1- Radio Shack SPL meter with integrated Mic.
2- Neuman U47
3- Neuman KM184
4- AKG 414 BLXII (Multi pattern)
5- Rodes K2
6- Sure SM 57 and 58

Obviously a couple are real high quality mics, but I also know that some have a tendency to spike up the high end. I guess my options are use them and don't worry, just pick which ever, or find some calibration files for one of them, buy FuzzMeasure and use the calibration file so the app knows what to do.

I need to use FuzzMeasure to see what the room nodes look like and improve it with sound treatment. I'd like to use waterfall, so I'm gonna buy this puppy at some point, but I'd at least give it a try with a decent start point.

Thanks
R

I’d be interested in seeing your results. Can you load the file somewhere we can dowmnload it?

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.

> According to IEC 60268-5 (Sound system equipment Part 5: Loudspeakers), THD must
> be reported along with the frequencies at which they were measured. So, if you want
> to give just one number, you'd probably just take a graph like the one I displayed
> above, and report the value at 1kHz.

Correct. But I’m thinking about a way to make a single number out of, say, the mean value of all frequencies... this would be new (I think), and, though still imprecise, better than the actual 1 kHz value that doesn’t say anything about the low end, for instance.

In any case, if you could make the distortion data exportable, it would make it really useful I think.

I think you mean to say you don't agree with a shifted display. The current THD graph that ships with FuzzMeasure 3.0 is shifted so that at 1kHz, you see the distortion components for 1kHz. That means the 2nd harmonic distortion value at 1kHz is the measured value at 2kHz, and the 3rd harmonic distortion value at 1kHz is the measured value at 3kHz.

If I do not shift the display, and leave it untouched as Farina does, it is up to you to mentally determine that the 2nd harmonic distortion value for 1kHz is the value you read at 2kHz. The more I think about it, the more I realize this is actually more confusing because you cannot easily visualize a range of frequencies that are free from distortion.

At any rate, the actual value people can relate to is either (a) harmonic distortion %, or (b) total harmonic distortion %.

Calculating (a) requires that you report the values for individual harmonics, as I currently do. So, you'd show a graph similar to the one I report now with 2nd and 3rd harmonics to properly display (a).

Calculating (b) requires that you figure out harmonic distortion up to some upper limit of harmonic (say, the 8th harmonic) and then combine them to figure out the total harmonic distortion.

As far as I can tell, there is no such thing as 'one number' for THD. When you see a single THD percentage reported in specifications, I'm pretty sure they must be reported with a reference frequency. So, 0.001% THD for a piece of equipment is probably calculated at the 1kHz point, and only up to some arbitrary upper-limit harmonic.

According to IEC 60268-5 (Sound system equipment Part 5: Loudspeakers), THD must be reported along with the frequencies at which they were measured. So, if you want to give just one number, you'd probably just take a graph like the one I displayed above, and report the value at 1kHz.

However, I wouldn't recommend this. If you need accurate specifications to report only a single value for THD, you're best served by the single sine wave method. FuzzMeasure's mechanism for calculating harmonic distortion will give you a very informative overall graph of the distortion behavior of a system—it tells you far more than a single number ever could.

Personally I don’t agree with this “no-horizontal-shift” display. I find it counter intuitive since the trace is not where you actually hear it, i.e. H#2 for 1 kHz is a sound that is clearly heard at 2 kHz, not at 1 kHz...

And for %, I would prefer a single THD number.

This said, your example is very interesting as well. Maybe we could have both ways available (“Harmonic distortion [Farina]”, and “Harmonic distortion [realigned]”)

By extension, would it be possible to also measure non-harmonic distortion (for PCM converters, for instance)?

The more I work on this, the more I think that neither approach is good. :)

I think that harmonic distortion graphs are just going to have to display % and only the distortion values. See this graph for an example:

http://www.supermegaultragroovy.com/i...

The lighter green is the 2nd harmonic, and the darker green is the 3rd harmonic.

Thend makes a good point above about the automatic windowing, though. By default I'm using a rectangular window, which isn't ideal. I should instead be using the Tukey-style window as proposed by Müller's paper.

So, there's definitely still some work to be done here, though I think that the % display is already a huge improvement.

We're definitely still ISO 3382 compliant here. The ISO 3382 merely states that the individual bands must be filtered by fractional octave (or third-octave) filters (preferrably the ones defined by IEC 61260, which is what I implement), and the calculation of the curve to be estimated is done using the energy decay curve for each band.

How the reverberation time estimation is done is left as an exercise to the reader of the spec. You can actually use FuzzMeasure to do a manual implementation of ISO 3382 to find T20 (for example) by the following:

1. Create an octave band decomposition of the signal
2. Switch to the energy decay curve graph in the impulse view
3. Visually determine the points at -5dB and -25dB for a given octave band
4. Visualize a straight line that fits between the -5dB and -25dB points
5. Extend that line to intersect with -60dB on the Y axis

T20 is the time between the 0dB point and the -60dB point you found using the method above.

Obviously, it's better you let my software do this automatically for you. ;)

Sounds right. – Jean-Pierre Côté, on July 03, 2008 14:24

It definitely is a change for the better. The drawback is the extra manipulation involved for the user that makes the time needed substantially longer. So, yes, an “automatic” feature would be appreciated. I’m also thinking about less skilled users who may get confused by this approach ...

BTW, are we still ISO 3382 compliant with this new method?