REW 5.40 beta 104: Measurement - frequency scaling issue

[ska]

Hi John,
Recently I tried to measure frequency response of my DAC at 44.1K SMPS using the latest REW beta version.
I noticed strange droop of the response starting from 18K. Then I switched sampling frequency to 48K and response became exactly like simulated for 44.1K.
In order to proof that the problem is in the REW software, I thoroughly measured the amplitude at 44.1K by digital oscilloscope. The real response was flat to 20KHz, as predicted. Please check frequency scaling in Measurement. Looks like frequency scale is a bit shrunk, like if you multiplied by (44.1/48) twice for shifting from 48K->44.1K.
Regards

 

[John Mulcahy]

REW can only control the interface sample rate if you use ASIO or WASAPI Exclusive Java drivers (device names starting EXCL). If you use the standard Java drivers the OS will resample the data to the rate in REW if the device sample rate is different and you will see the effects of the resampling.

 

[ska]

John,
Thanks for the prompt reply.
I double checked the setting, the issue is still there.
Verified using averaged periodic white noise as well.
Please look at the attached images.

But digital scope (LeCroy 500MHz) still displays absolutely flat response at 20K as predicted by math.
Regards,
ska

 

[ska]

Ooh, sorry. I forgot to check E1DA (ESS A/D chip) response at 44.1K. That might be the root cause.

 

[John Mulcahy]

Could be. There's nothing in REW that could roll off the response.