FSAF (Fast subband adaptive filtering) measurement

[John Mulcahy]

I took FSAF, acoustic, and regular sweep measurements. Distortion levels differ by a factor of 10.

There are several differences.

• The stimulus is not the same
• Sweeps have low crest factor (the peak is only 3 dB above the rms level) so for a given rms level the signal peaks are much lower than for noise or music signals. As distortion is level-dependent that means lower distortion for a given rms signal level
• Sweeps measures harmonic distortion and THD, FSAF measures TD+N and so includes both harmonic distortion and intermodulation

Increasing signal level will initially improve signal-to-noise ratio as the signal increases but the noise does not, until the increased signal level brings distortion above the noise.

 

[sm52]

Thanks for answers. I have attached the measurements. Why does REW determine the peak time of the impulse of the FSAF measurements differently?

 

[John Mulcahy]

Noise floor looks high. Since input and output are on the same interface you don't need to use timing markers.

Why does REW determine the peak time of the impulse of the FSAF measurements differently?

I'm not sure what is happening with the file measurements. Does the track start quietly? REW may be struggling to correlate the track start with the incoming data, you can pick a start time further into the track where it has good levels to see if that helps.