ADaU1442 R/L mixer issue

Hi Hans,

Could you please upload a simple version of the SigmaStudio .dspproj file to your post so I can look at it?

Dear Brett,

Please find the attachment.

Thanks and best regards,

Hans Xie,

S.FA Manager

Excelpoint International Trading (Shanghai) Co.Ltd.-Xiamen Branch

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发件人: BrettG analog@sgaur.hosted.jivesoftware.com

发送时间: 2011年3月12日 3:30

收件人: Hans Xie

主题: New message: "ADaU1442 R/L mixer issue"

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ADaU1442 R/L mixer issue

reply from BrettG <https://ez.analog.com/people/BrettG>; in SigmaDSP Processors - View the full discussion <https://ez.analog.com/message/20901#20901

please find the attachment.

Unfortunately there was no .dspproj file included in the attachment. Could you please try again?

Sorry,please find the attachemnt with pro.

Br,

Hans

Hi Hans,

Unfortunately, I do not see the same results as you are seeing. First I tested the output of the circuit with a white noise source. You can see I got a flat response:

Then I turned the noise source off and saw the noise floor drop:

Here's a close up of the spectrum with the mute disabled:

Here's with the mute enabled:

The level went down slightly, but the frequency response didn't change.

Then I tried to read back the signal levels directly in the project. With no mute, the white noise source's RMS level is 0.25, and the output's RMS level is 0.5, which makes sense because we're summing two noise signals together with 0 dB of gain:

When I activate the mute, I see that the level drops down 6 dB to 0.25, which is what we expect because one input to the mixer is inactive:

If there was any attenuation of high frequencies in the mixer, that number would definitely be less than 0.25. So, I definitely am not getting the same results as you.

By the way, the mixer's internal algorithm only uses addition and linear gain. It has no frequency-dependent operations, so it could not change the frequency response in any way.

I was testing this on the EVAL-ADAU1442EBZ evaluation board. It's possible that if you are using another board, the other hardware (such as converters) are playing a role on your measurements.

Dear Brett,

thanks for your great support, after long time debugging we find there is wrong configure from the I/O input LRC (POS)register.and the issue settled.

Thanks again, cheers!

Hans