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noisy output from aic3106

Donald Reay
Expert 1545 points

Has been discussed on OMAP forum but no conclusion reached.

Whether I use the test program supplied with the board or the PSP audioSample example I seem to get a lot of noise on both the line and high power outputs from the OMAP L137 EVM. Has anyone else experienced this? Is there a way of getting a cleaner output? Below is line output when 1kHz sinusoid is input to audioSample program. Result is very similar when test program supplied with board generates a 1kHz sinusoid using a lookup table.

 

  • 0
    TI__Intellectual 1305 points

    The amplitude of the sine wave seems to be very low. Have you tried increasing the input volume of audio?

    Also please try giving any song as an input and check the result.

  • 0 in reply to Nagabhushan Reddy
    Expert 1545 points

    The amplitude is limited by the aic3106 AGC acting on the input. If I change the gain specified in audioSample_io.c from 70% to 100% a larger output signal is possible but the noise appears to have a similar amplitude.

     

    Here's a bit of output for music input - AGC gain 100% - I think the same noise is apparent.

  • 0 in reply to Donald Reay
    TI__Guru 61456 points

    The output signal from the AIC3106 looks ok. The codec architecture is delta-sigma, which pushes (and shapes) quantization noise out of the audio band. What you see here is the high-frequency noise, which is expected and inherent to the design.

    If you hook this up to a speaker, the noise won't be audible due to its high frequency (it will all be shifted above the audio band, e.g. above 20kHz, if you sample at 44.1kHz).

    You can verify this by running the signal through a spectrum analyzer and looking at the result in the frequency domain.