FSAF (Fast subband adaptive filtering) measurement

John Mulcahy

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I removed the sock, and added a LR2 high pass at 20Hz. The result of this FSAF measurement confuses me, as the total distortion is reduced through the entire spectrum of the speaker, right up to 20kHz, and significantly so as well. Is there a reasonable explanation for such a change in TD throughout with only a 20Hz high pass applied?
It does seem odd, perhaps Michael will have some ideas. If I run tests over a loopback connection with artificially induced distortion the results are not affected by adding a HP on the stimulus. I wonder if room resonances are having an effect on the process and the HP is attenuating the lowest resonances? Could try higher HP frequencies and see if the results stabilise.
 

dcibel

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Yes, the results are as expected if I compare for example a 100Hz high pass to 200Hz high pass, in that the tweeter distortion stays at the same lower level. It only becomes elevated when I include some subsonic noise in the stimulus.

I'll see if I can generate some audio track with a low frequency noise superimposed to compare with real audio.
 

Berndh

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It is the spectrum of the residual
Yes - Harmonics (Distortion), IMDs and (Barkhausen-)Noise,
like one would see on an spectrum-analyzer (on peak hold?), analyzing the residual audio (file).

the fundamental graph is the spectrum of the linear part of the response
No, it is the transfer function of the DUT


You all are stuck in e.g. Farina THD 2...9
get over that useless metric!

Listen!

Best regards
Bernd
 
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Berndh

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@dcibel: I replicated your hpf results. It is Barkhausen noise elevating your high frequency in TD+N graph. Listen!

@John Mulcahy: Sorry, i got lost in a kaleidoscope.

Best regards
Bernd
 

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dcibel

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You've only shown that noise level of the residual is increased, this much is obvious from the graph. Please let's not jump to conclusions.
 

FSAF

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@dcibel: I replicated your hpf results. It is Barkhausen noise elevating your high frequency in TD+N graph. Listen!

@John Mulcahy: Sorry, i got lost in a kaleidoscope.

Best regards
Bernd
Barkhausen, which is described by the same math as quantum mechanics, is not the simplest way to analyze the problem. Please let me think of a way to explain it through hysteresis. It may take a few days.
 

dcibel

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@dcibel: I replicated your hpf results. It is Barkhausen noise elevating your high frequency in TD+N graph. Listen!
Since you've posted the details of your measurement conditions elsewhere, I want to be clear that I am not questioning the ability of a driver to generate distortion products higher up in frequency when excited with low frequency signal. I am questioning how high frequency distortion propagates to the tweeter output in a 2-way passive speaker, and only in response to input stimulus, not directly correlated to cone excursion.

Your post here implies that you've tested a single driver, which is not a replication of my test or concern.
 

dcibel

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I think the primarily FSAF does not work well into subsonic frequencies, as Mike suggests in post 134.

I think part of my problem may be that Motu claims a DC coupled input, so subsonic noise is throwing things off a bit. For example, I found my repeatability problem with a questionable electrical switch contact helped a lot, but not a 100% resolution. Background noise is of primary concern, and I found I got more reliable results by lowering the IR length from 500ms to 200ms, however overall distortion level is increased when I do this, which again, is confusing.
 

Berndh

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2-way passive speaker
and now?
you blame REW for revealing...
you blame FSAF for revealing...

what is next to blame?

a switch... haha Wackelkontakt ...another thread cluttered with Wackelkontakt

Not the switch?
Not the "jig"?

tweeter output
You definitely measured the tweeter output? - how do I know that's nonsense? ;-)

Best regards
Bernd
 
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dcibel

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I'm just going to ignore you now. Right or wrong, your comments are not enlightening or encouraging, they are condescending. Nobody will see the light with that attitude.

I will continue evaluating on my own.
 
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FSAF

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dcibel

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Read through the document tonight. I like that it was presented in a manner that a basic human like my self could understand, and I particularly related to section 3.1 :)

Reading about measurement methods and noise reinforced that I am headed down the right path with my own speaker testing / evaluation regimen. I agree that displaying harmonics at their harmonic frequency is a better view of reality, though I usually don't present data in this way to others since it will just confuse things since harmonic data is usually presented differently.

It also suggests that I should consider my large condenser mic for distortion testing, so I will evaluate that. Mine is a low cost MXL 770, but with the diaphragm replaced with a nice "K 47" style 1" capsule.

FWIW, a driver that will soon see the gauntlet of FSAF is Wavecor WF120BD03. Displaying harmonics at the harmonic frequency shows that nice flat line 3rd harmonic, at a nice low level of 0.1%. It may not be until next week when I complete further testing however.
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