Frequency response: nothing above 25kHz

JLM1948

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Thread Starter
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Jan 12, 2019
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124
Hi,
I have recently purchased a Cosmos ADC
and a Topping E30 DAC
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?
 

sam_adams

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Joined
May 23, 2017
Messages
285
You will have to change the DAC's output filter to the Super-Slow Roll-off filter:

46672


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

John Mulcahy

REW Author
Joined
Apr 3, 2017
Messages
7,212
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

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Jan 12, 2019
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124
Spot on, John! Cosmos ADC is now good at least up to 170kHz.
 

JLM1948

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Thread Starter
Joined
Jan 12, 2019
Messages
124
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)
 

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