FSAF (Fast subband adaptive filtering) measurement

sm52

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Mar 14, 2019
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As I assume, for FSAF you need to choose a signal level at which the noise level will be minimal. And this is not the highest signal level. As the signal level increases from the optimal level, the noise will also increase. Well, it's worth waiting a little. So John can implement improvements.
It will take me a few days to check-in and upload the update, and then John will be able to integrate it.
 

Berndh

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Sep 19, 2023
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Please let's not jump to conclusions.
Yes, sir
Simply adding the low pass gets rid of the crackling, the high frequency products are now absent despite the driver producing the same bass output.
No, sir

This time it is more complicated ;-)
Attached are two (FSAF residual audio) files:

The "rew filtered" file was made with full range grey noise file set for excitation.
The filters set in REW FSAW were: L-R8 hpf 40 Hz and L-R8 lpf 2kHz

The "pre filtered" file was made with pre filtered gray noise file set for excitation.
The gray noise was low pass filtered in audacity with 48dB/oct low pass filter at 2kHz, exported as .wav.
The filters set in REW FSAW were: L-R8 hpf 40 Hz (and L-R8 lpf 20kHz)

So the (audible) excitation while performing the measurement was the same for both residual files.
(even the crackling above 2 kHz was audible same while measuring.)

Now please listen:


@FSAF : why?

Best regards
Bernd
 

Attachments

  • 20241114 filtered residuals .zip
    2.7 MB · Views: 1

dcibel

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Sep 10, 2017
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If I understand correctly, you are comparing two "identical" files, one is a pre-filtered file, and the other is filtered by REW.

I reproduced your test, however using REW's generator for pink noise. In Audacity, I set HP 20Hz/12dB, and LP 1000Hz/48dB. In REW, I used 20Hz/BU12 and 1000Hz/BU48.

Comparison of measurement has slightly different output level, because of the HP applied to the pre-filtered file, the RMS level of the rest of the spectrum is slightly elevated. Not enough to make a big difference for this comparison, but difference would be even greater had I used 40Hz HP.

The residual produced is rather similar on my end, and I think any difference can be observed by review of the accompanying charts and graphs.

Compare FR - REW is somehow able to extrapolate the entire frequency response of the driver using a pre-filtered audio file that effectively produces no output beyond 3kHz.
1731617378446.png


Distortion levels are resulting from change in SPL: only, and small difference is observed at 10kHz at the driver breakup.
1731617512422.png



Reviewing the fundamental, because REW has extrapolated the entire frequency response for the pre-filtered measurement, there is a difference in fundamental present, somehow extrapolate from noise.
1731617575418.png


To confirm, noise floor is very similar between both measurements.
1731617667703.png
 

Attachments

  • filter comparison.zip
    5.3 MB · Views: 44

dcibel

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Sep 10, 2017
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246
Difference in level was 3dB between pre-filtered and REW filtered measurement. When I adjusted the level by 3dB, overall distortion levels are very comparable. This in interesting, however has not changed the conclusion I jumped to earlier ;).

1731619244544.png
 
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