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TLV320AIC3254EVM-K differential microphone

Mario Raffin
Expert 2405 points
Other Parts Discussed in Thread: TLV320AIC3254EVM-K

Hi,
with TLV320AIC3254EVM-K, I configured Audio Recording as Differential On-Board Microphone and if I try to record a wave file I have a DC component, as you see in the image.


There's a way to avoid this DC component?

Best Regards.

  • 0
    TI__Mastermind 46195 points

    Hi,

    There is a table of common jumper configurations (including differential) in the EVM schematic. This is available in the TLV320AIC3254EVM-K User Guide. Have you checked these setting are correct?

    Thanks,

    J-

  • 0 in reply to J-
    Expert 2405 points

    Hi J-,

         thank you for the support. The jumper settings seems to be correct according to the user guide.

    I have:

    W2 IN 

    W3 IN

    W4 OUT

    W4 IN

    W6 IN

    W7 IN

    W8 2-3

    Best Regards.

    mario

  • 0 in reply to Mario Raffin
    TI__Mastermind 46195 points

    Hi Mario,

    Here is what I get with my EVM:

    The offset is around -0.005 FFS.

    I think I know what is going on. The descriptors of our previous USB audio firmware version (2.03) causes our USB controller to identify itself as a microphone. On Windows Vista onwards, this causes the OS to automatically add ~30dB of digital gain. This correlates to the fact that you are observing around -0.15 FFS of offset (0.005*30dB = 0.16 FFS).

    We updated our USB firmware as a line input so that Windows will not perform this automatic gain boost. The latest f/w files can be found in http://www.ti.com/lit/zip/slac563. You can reflash the f/w by following the steps in 'AIC3254 CS > EEPROM Writer'. Once updated, I recommend you to uninstall the previous USB-miniEVM in Device Manager and reconnect the USB cable. It should then show up as a USB-AudioEVM in the AIC3254 CS main panel, version 3.04 (or newer).

    If you run into any trouble, please refer to this wiki page: http://e2e.ti.com/support/data_converters/audio_converters/w/design_notes/2790.how-to-revive-an-aicdacadc-evm.aspx

    Thanks,

    J-

  • 0 in reply to J-
    Expert 2405 points

    Hi J-,
        I understand.  Apart from the gain, in my application the offset is not negligible compared to the signal and this produce some issue on the post processing. 

    So  I wonder whether there is a workaround available to remove this offset, hardware or software (miniDSP?).

    We already developed a board with this codec and I absolutely need to remove the offset from the signal.

    Best Regards,

    mario

  • 0 in reply to Mario Raffin
    TI__Mastermind 46195 points

    Mario,

    You can do a high pass biquad filter in the miniDSP. Use the 'multi-biquad' component. This will remove any offset to 0.

    Again, the offset you showed is not really the offset from the AIC3254 itself.

    Regards,

    J-

  • 0 in reply to J-
    Expert 2405 points

    Hi J-, 

       thank you for the reply. I think that the IIR filtering is not a good idea for my application since the echo cancellation algorithm does not like this kind of processing. I could implement an HP-FIR or maybe it could be easier to apply an offset which removes the one introduced by the adc.

    In any case, since I am working on a new design, I would like to understand if it is possible to remove this 0.005 FFS (more than 7 bit) with some design trick.

    Thanks,

    mario