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PCM5121: Unable to get the Flat Frequency Response with respect to 20hz to 20KHZ.

Manimaran Murugesan
Prodigy 20 points
Part Number: PCM5121

Tool/software:

Hi,

We are verifying the Frequency Response with PCM5121 DAC in AP machine. But We are not getting the FLAT Frequency Response at anytime with respect to any of the "DSP Program" configuration.

We are always getting dip in the response at 1Khz to 2Khz and not stable. In respect to Vrms also we are seeing fluctuated VRMS values from 1.5Vrms to 2.896Vrms for 20hz to 20Khz.

How to achieve the Flat Frequency Response and constent VRMS for 20hz to 20Khz frequency. We were tried tuning the Gain, Volume and used Fixed Process Flow without any coeefficients applied, but still unable to achieve it. And then tried the same with PCM5121EVM-U with USB input and Analog Audio ROM process, There also we are not getting constent VRMS. Whenever Frequency increased VRMS gets decreased.

Could you please guide us to achieve constant VRMS and Flat Requency Response.

Regards,

Manimaran M.

  • 0
    TI__Mastermind 30241 points

    Hello,

    Can you please confirm the GUI and its version that you are using and send me few screen shots of your different testing so I can review and see what is going on.

    Thanks,

    Arash

  • 0 in reply to Arash Loloee
    Prodigy 20 points

    Dear Arash,

    Below Measurements are based on our product which is using PCM5121 as DAC.

    We have attached the Frequency Response and Different VRMS values comparison between 1KHZ_0db and 20Khz_0db sine waves.

    for 1Khz_0db = 2.076 Vrms & 20Khz_0db = 1.513 Vrms values.

    Frequency Response dip after 500hz, We have measured with AP(Audio Precision Tool). To avoid the ADC we have used Optical in and Analog Out(DAC out) for Measurement.

    We have used 5.95 PPS version for EVM and getting the same result. But we are expecting the Flat Frequency response.

    Could you please review and guide us to move forward to get Flat Frequency Response. We have tried tuning all Gain related registers but not helping us.

    Regards,

    Manimaran M.

  • 0 in reply to Manimaran Murugesan
    TI__Mastermind 46035 points

    Hi,

    Today is a holiday for our team in the U.S. We will follow up with you on Tuesday.

    Thank you for your patience,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    TI__Mastermind 30241 points

    Hello,

    The fact that you are plotting the gain and you see that your gain plot shows a similar behavior, makes me think something is going on with the internal set up.

    Can you load one of the preloaded ROMs and start from there or use  one of these codes that I am attaching in the zipped file below. It seems there is some filter being activated internally .

    Meanwhile, check the component connected to the DAC to make sure there is no LP filter with this signature attached to it, The correct way to debug is to disconnect the DAC from next stage and perform the test.

    1565.SLACC622_ sample code.zip

    Regards,

    Arash