FSAF (Fast subband adaptive filtering) measurement

[dcibel]

Thanks John. This FSAF stuff is really impressive, thanks for incorporating it to REW! I think it may take some time for it's use and benefits to really sink in to the general public however, but given some time perhaps FSAF will be as common of a term as HD or IMD.

 

[dcibel]

John, from some discussions at DIYAudio, should one expect some loopback test with a known harmonic distortion level and sine sweep stimulus, to provide the same overall distortion level when comparing HD sweep to FSAF? I would expect not, but I am also having a hard time determining the cause of a significant discrepancy in distortion level.

Here's a simple loopback test I completed, with an amplifier that exibits some power supply noise, result in the HD plot is effectively transformer hum and noise floor, not much else. I kept the signal level low to make sure the hum is clearly shown in the HD plot, and "show harmonics at harmonic frequency" used to make easier interpretation for direct comparison.

For FSAF, I used the signal generator in REW to export the same sine sweep at the same level to file. Confirmed level when running the measurement is very similar. Sweep is 0 to 48kHz, 5.5second long, no filters, and FSAF is configured for 500ms IR, and "no mic" selected since this is a simple loopback result.

You can see here, that the amp hum is much more discernible here, clear as day approaching 10%. It's probably not meant for such direct comparison, but I am just trying to understand the differences and put some context to the results of FSAF. Michael Tsiroulnikov seems to not be engaging with the public anymore, so any insight you can provide is helpful.