FSAF (Fast subband adaptive filtering) measurement

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.

FSAF said:

It will take me a few days to check-in and upload the update, and then John will be able to integrate it.

Click to expand...

dcibel said:

Please let's not jump to conclusions.

Click to expand...

Yes, sir

dcibel said:

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.

Click to expand...

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

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.


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



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.


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

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 .

Berndh said:

The "rew filtered" file was made with full range grey noise file set for excitation.
The filters set in REW FSAF 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 FSAF were: L-R8 hpf 40 Hz (and L-R8 lpf 20kHz)

Click to expand...

So virtually no LP/lpf was used in REW FSAF for measuring and generating my residual with the already LP filtered file.

@dcibel Thank you for replicating my experiment. And a big thank you for publishing your residual audio. "Hidden" in red letters is my guess. (If you allow me to guess ;-) )

@FSAF and @John Mulcahy : Thank you very much!! I see no need to change anything.

Best regards
Bernd

Sorry, perhaps I did not complete a perfect replication of your test. When measuring with the pre-filtered file, I turned filters in REW off entirely, and included the HP in the filtered file, so the comparison was entirely pre-filtered pink noise from file, vs REW fitlered pink noise on playback. A 20kHz LP seems a bit redundant since the file I created was already low passed at 1kHz.

dcibel said:

I turned filters in REW off entirely

Click to expand...

No, sir, you did not ! Period.

Both residuals were obtained with a 2kHz lpf, set in REW FSAF.