signal attenuation through EVAL-ADAU1452REVBZ analogue connectors

Hi there,

I've been trying to work out why when I try to make some reference sweep measurements through my eval' board I'm getting an attenuated signal.  To test this, I sent a 1 kHz tone at 2.56 Vrms to analogue channel 0 (measured at the connector on the eval board), and through a signal path with no attenuation or gain applied, then measure the voltage at the 3.5mm output connector and I'm only measuring 0.6 Vrms.  That's approx' -12 dBV difference through the board.  What is going on?  Where is my signal getting attenuated?

Kind regards,


  • 0
    •  Analog Employees 
    on May 10, 2020 2:47 PM

    Hello Mark,

    The EVAL-ADAU1452REVBZ has a full-scale analog input level of 1V RMS. The full-scale analog output level is also 1V RMS. I expect your test signal is clipping the ADC; this would look like attenuation on a level meter.

    I usually set test sources at 0.9V RMS so that the input filter op amps are not close to clipping. If you adjust your 2.56V RMS source to 0.9V is the attenuation still there?

    Also, if your tone source has high output impedance there could be attenuation through the evaluation board's input filter stage.


  • PDF

    Hi Joshua, thank you for your response.  Yes, I misread the data sheet and since my post (just this morning in Aus') have re-run my testing.  I am still getting attenuation.  The attached PDF indicates the steps I took this morning, I'll summarise as follows:

    STEP #1: this was me basically calibrating the levels to and from my soundcard analogue inputs and outputs.

    STEP #2:  I first generated a 1 kHz sine wave from within my measurement software (WinMLS) at -24 dBFS which resulted in a signal level of 0.69Vrms at the 3.5mm input socket terminals on my EVAL-ADAU1452REVBZ board.

    STEP #2 Observations shows voltages measured, and some strange readings.  Can you respond to these?

    I end up with just noise when I try and measure a signal through the EVAL-ADAU1452REVBZ board; the signal is attenuated too much...



  • Thanks for your responses, Joshua!

    Your responses to questions 1 thru 4 are great!

    Regarding question 5.  Yes, I have been using a sine sweep for my measurements.  I regularly measure lots of different audio equipment, including electronic measurements, but I have not seen such variability in responses when simply running the same measurement over and over...  When no settings have been changed of course...  Is there perhaps some dynamic processing in the AD1938?  What else could cause this?BasicLoopbackTemplate.zipI've attached one of my basic loopback testing projects so you can see that there is no other processing in-line...  

    Oh, I figured that since I could place an AD193x IC into my SigmaStudio design that I might also be able to interrogate the chip on the eval' board.  I'll try and work something out.

    Regarding scrolling in windows.  All my other TABS and settings windows have scroll bars, but the Hardware Configuration tab for the AD193x register controls does not.  It's the only one that doesn't...  Shame...  (Yes I confirmed Windows settings).  Any further ideas why this may be?

    Kind regards,


  • +1
    •  Analog Employees 
    on May 13, 2020 8:34 PM in reply to MDThommo81

    Hello Mark,

    Let me chime in here since I support the AD1938 and the ADAU1452. 

    One of the changes we did on the Eval-ADAU1452RevBZ verses the older Eval-ADAU1452MINIZ is that it is possible to change the codec to be controlled from SigmaStudio. I detailed those modifications in the user guide for the eval board. It is a bit involved of a mod but it is possible. 

    The codec will come up with the default settings with only a few exceptions when in standalone mode. The differences in standalone mode are detailed in the datasheet if I remember right. The volume controls will be up at 0dB with no attenuation when it powers up. Standalone mode will not change this at all.  

    Regarding the scroll tabs for the GUI. This is an older GUI and there are not very many controls for this part. Obviously the programmer did not enable scroll bars in the window object which I agree is an oversight. I have not noticed this since I usually have enough room on my screen. You might have to close out the output window or the Tree Toolbox window to make some room. 

    I reported this in our work request system for the programmers. 

    Now regarding your test inconsistency. I suggest you try to isolate if it is the input to the DSP or the output. 

    I have not looked at your project but you can do two things. You can setup an oscillator in the project to send out to the DACs. The oscillators are at 0dBFS so you can see how you are measuring this externally. You can change the frequency and test the performance. 

    Then you can use the meters to look at what level is coming into the DSP. Keep in mind that the meters in SigmaStudio are not meant to be precise reference level meters but they still can do a decent job of reading the level. The only thing that I wish were different is that the programmers set it up so that a 0dBFS signal will read as -3dB. So keep that in mind when looking at the incoming levels. 

    Dave T

  • Hi, Dave!  Thanks for your responses too!  That is very helpful.  

    I'm a little nervous about ruining my Eval' board, however the instructions in the updated User Guide for undertaking the modification seem pretty clear.  If you look at the example file I put together in the attached Zip file, I'm assuming that this is how I configure the software (after implementing hardware mods) to then be able to also interrogate the AD1938 IC?

    I can try your suggestion with oscillators to test the DACS, however, I'm not too concerned if there is an overall level difference through the device, what is very important is consistency.  I can easily reference the signal path through the Eva' board to overcome any frequency dependent anomalies, however, what I am seeing is a different IR every time I make a measurement through the board.  Therefore, referencing is not possible, and I can't confirm operational consistency. 

    I've also included a collection of IR measurements I have made through the Eval board, using the included simple SigmaStudio file.  Every measurement is different! 


    The similarity between concurrent measurements would ideally be identical, or almost identical (I'll also included some loopback measurements through my soundcard (SC) for reference.  My main focus is on the pre-ring in the IR's having significantly different amplitudes, and I'm wondering where the ringing is coming from (and hence my need to retrieve the Codec parameters so I can see what filtering etc is active to see if that is contributing).

  • Hi Dave,

    I have modified my Eval-ADAU1452RevBZ board as per your instructions in the user guide.  I appear to be able to read the settings from the Codec now.  However, now I am not getting any signal into, or out of, the SigmaDSP chip!  I can measure correct voltage at the analog input terminals, but they don't meter inside the DSP when monitoring using SigmaStudio.

    I setup a pink noise generator inside SigmaStudio to test the output, and whilst I do get metering inside the DSP now, there is 0V at the analog outputs!

    What has happened?  How can I get my eval' board working again?

    Kind regards,


  • 0
    •  Analog Employees 
    on Aug 21, 2020 3:49 PM in reply to MDThommo81

    Hello Mark,

    I have been a bit overwhelmed the last few months. Sorry I missed this message. Do you still have this issue?

    Dave T

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