| Changes
In my and obviously others experiences the Measurements do change. This seems to be widely understood and dealt with. High end equipment makes a number of sweeps in each band to be sure of a result. There are 'quality indicators' provided to give an idea of how valid. Sometimes the result is rejected and one has to go again. I believe REW has this quality or confidence feature?
Two of us have suggested reasons why this happens at LF. i.e. The Stimulus signal is quite variable. If you stop a 63 Hz tone or third octave of pink suddenly, the waveform and energy content will be very different at each random stop. Also the period of the Waveform can be close to the first 10% of the slope used to derive EDT. Take a look at the waveform of some recorded third octave 63Hz and you will see what I mean.
I don't know if this old school tone burst understanding can be translated to Sine Sweep and MLS methods but I suspect similar anomalies will happen. I note REW does not do RT below 80Hz. Rather than present unreliable info John has left it out, a reasonable call IMHO.
Regarding the Non Linearity. That seems a bit deep, and Ethan can turn into a bit of a Terrier sometimes....:-) However, just out of interest, I also would like to see some numbers on the Non Linearity alluded to
i.e. what type of change, how much in level or time, at what frequency area, at what SPL?
Rufff, DD |