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PCM5122: The Output are always the same.

Andrew Buckin
Expert 2130 points
Part Number: PCM5122
Other Parts Discussed in Thread: DAC80502, DAC8822, DAC11001A, PCM5100A

Help me please with understand why this is so. PCM5122. I am studying the work of PCM5122. I'm using Raspberry Pi. Everything works well.

I can't figure out why the output always looks the same in any samplerate.

I expected to see something else. BCK and LRCK change correctly.

code and pictures on  karu2003/HiFiBerry_test (github.com)

where do these waves come from and why do they not change when the samplerate changes?

Thank you.

Andrew.

  • 0
    TI__Guru 53983 points

    Hi Andrew,

    This device features an interpolation digital filter.  The digital filter will create additional samples based on its architecture (there are a few options in the device).  From a practical perspective, the device will interpolate up to 384kSPS (for 48k× based samples) or 352.8kSPS (44.1k× based sample rates).  This means that the device can use the same output filter regardless of sample rates.  There are some options in the register map that you can use to disable this, but you will likely see degraded performance when using a lower sample sample rate.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Expert 2130 points

    Thank you.

    I found it. "selectable by writing to Page 0, Register 43, D(4:0)."

    just did not find where to turn it off. :( 

  • 0 in reply to Paul_Frost
    Expert 2130 points

    I looked at the driver for Linux. This setting can be changed through ALSAMIX.

    If i enable "Fixed process flow". I dont see Output.

    I need a program for "Fixed process flow".

    Where can you find sample programs for "Fixed process flow"?

    Andrew.

  • 0 in reply to Andrew Buckin
    TI__Guru 53983 points

    The fixed process flow is detailed in the device datasheet, but you can customize the values using PurePath Studio.  This lets you implement some BQ filters and a DRC.   Using the fixed process flow with custom DSP coefficients means that you have to write ~1000 registers to the device, so keep that in mind if you want to go this route.  

    If you are trying to disable the digital filter (I am not sure why you want this), you could change the setting in register 34 to the "octal" speed setting.

    Perhaps you could tell me what you are trying to implement in your system, and I can make a recommendation on the best device/configuration to use?

  • 0 in reply to Paul_Frost
    Expert 2130 points

    I want to make an single echosounder (Altimeter) on Raspberry Pi for my ROV. I have a proven AFE. I don't need filtering. Since there is analog flirtation in AFE. I need a signal with no output delays.

  • 0 in reply to Andrew Buckin
    TI__Guru 53983 points

    Hi Andrew,

    You could consider the PCM5122 using the low-latency filter, which is <2 samples of delay.  But if you want a true zero-latency, then you should look at our precision DACs.  You could consider a device like the DAC80502, or the MDAC DAC8822, or the ultra-high precision DAC11001A family of devices.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Expert 2130 points

    thanks for the help,

    DAC11001A for the future. :) i bought a PCM5100A for RPi.

    and made a sweep test generator. karu2003/sweep_gen (github.com)

    Now I will think how expensive it is to receive a signal.

    The topic can be closed.

    Andrew.