Frequency response: nothing above 25kHz

[JLM1948]

Hi,
I have recently purchased a Cosmos ADC

Cosmos ADC | index

e1dashz.wixsite.com

and a Topping E30 DAC

E30 Multi-input PCM768\u0026amp;DSD512 DAC-TOPPING

The ADC is supposed to offer a HF limit of about 190kHz at 384k SR.
I'm not so sure about the DAC, which may be limited to about 90kHz.
I have installed the latest version of REW (32bit) on my notebook. I use FlexASIO. The OS sees both the ADC and the DAC.
I have tried to measure the response of the complete chain, but got only garbage.
So I connected my analog signal generator that goes up to 200kHz to the ADC input, and visualized levels in REW.
I found out that the level indication falls rapidly after about 24kHz. I've repeated the test many times and I came to the conclusion that there is a filter that cuts off HF; now, is it in the ADC or in REW? Am I wrong in assuming that the meters should not low-pass teh signal?

 

[DanDan]

REW is probably running at 48K

 

[sam_adams]

You will have to change the DAC's output filter to the Super-Slow Roll-off filter:

You will also need the driver for the E30 DAC when using it on Windows.

 

[JLM1948]

REW is probably running at 48K

If it did, why would it show 384k in the Preferences?

 

[JLM1948]

You will have to change the DAC's output filter to the Super-Slow Roll-off filter:

even with the steepest filter, response is supposed to go up to 0.35Fs; that would be in excess of 130kHz.

You will also need the driver for the E30 DAC when using it on Windows.

I use the dedicated driver, wrapped in FlexASIO

 

[John Mulcahy]

Check the sample rate for the default format on the Advanced tab of the Windows audio properties for the ADC, ASIO wrappers can still be affected by the underlying Windows settings.

 

[JLM1948]

Spot on, John! Cosmos ADC is now good at least up to 170kHz.

 

[JLM1948]

After some tweaking, I got both the ADC and DAC working, but it's not quite satisfactory.
See the frequency response. The graph shows the response in all 6 different filter modes, which apparently default to the same at 384k.
Below is the same type of graph at 96k SR (from the brochure)