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Noise in ADAU1361 recording

Hi,

I am getting continuous noise in background when I play the file recorded using Microphone. I have connected MIC on headphone Jack, there is no noise while playing other files (not recorded by MIC) on Headphone out.

Below is the schematics, Can you please suggest if I need to tune or modify anything in HW. Also please suggest if there are any Software configuration related to PGA or ALC that needs to be tuned properly. 

Regards,

Ani

  • Hello Ani,

    Unfortunately the schematic you uploaded is not very legible. It is too grainy and blurry for me to be certain how the mic is connected.

    Maybe try to upload in a couple of smaller parts of the schematic? Sorry for the trouble.

    Can you hear any of the desired microphone signal or is it just noise with no signal?

    If it is just noise then I suggest you take an oscilloscope and look to see if you can see the microphone signal at the pin of the codec input. So this would let me know that the microphone is at least putting out something.

    Next, I need the register settings of the codec.

    Are there other analog input sources that work? Do you have the Aux in being used or one of the other inputs? You mentioned that it is fine playing back recordings but that is just using the DACs. Is anything working on the ADC side of the codec?

    Keep in mind you can route the record signal directly to the output DACs inside the IC while the signal is still analog. This is also a good test of the microphone input.

    I know you are not using SigmaStudio but I suggest you download it and use it to see the signal flow. The diagrams are helpful and it will also help you see which registers you need to set.

    Thanks,

    Dave T

  • Hi Dave,

    Below is the schematic image. Hope its clear now.

    We are able to hear desired voice in recorded audio with lot of noise in background.

     We will use sigma studio and check the register settings.

    Adress 0x4000
    0x01
    Adress 0x4001
    0x00
    Adress 0x4002
    0x00
    Adress 0x4003
    0x00
    Adress 0x4004
    0x00
    Adress 0x4005
    0x00
    Adress 0x4006
    0x00
    Adress 0x4007
    0x00
    Adress 0x4008
    0x00
    Adress 0x4009
    0x00
    Adress 0x400A
    0x00
    Adress 0x400B
    0x00
    Adress 0x400C
    0x00
    Adress 0x400D
    0x00
    Adress 0x400E
    0x00
    Adress 0x400F
    0x00
    Address = 0x4010
    0x01
    Address = 0x4011
    0x12
    Address = 0x4012
    0x00
    Address = 0x4013
    0x00
    Address = 0x4014
    0x00
    Address = 0x4015
    0x00
    Address = 0x4016
    0x00
    Address = 0x4017
    0x00
    Address = 0x4018
    0x00
    Address = 0x4019
    0x00
    Address = 0x401A
    0x00
    Address = 0x401B
    0x00
    Address = 0x401C
    0x00
    Address = 0x401D
    0x00
    Address = 0x401E
    0x00
    Address = 0x401F
    0x00
    Address = 0x4020
    0x00
    Address = 0x4021
    0x00
    Address = 0x4022
    0x00
    Address = 0x4023
    0x96
    Address = 0x4024
    0x97
    Address = 0x4025
    0x00
    Address = 0x4026
    0x00
    Address = 0x4027
    0x96
    Address = 0x4028
    0x00
    Address = 0x4029
    0x00
    Address = 0x402A
    0x00
    Address = 0x402B
    0x00
    Address = 0x402C
    0x00
    Address = 0x402D
    0xaa
    Address = 0x402E
    0x00
    Address = 0x402F
    0xaa
    Address = 0x4030
    0x00
    Address = 0x4031
    0x00
    Address = 0x4032
    0x3f
    Address = 0x4033
    0x3f
    Address = 0x4034
    0x1f
    Address = 0x4035
    0x00
    Address = 0x4036
    0x03
    address 0x4011 = 0x12
    0x00
    
    

    Thanks ,

    Anirudha

  • Hello Ani,

    Thanks for making the additional screenshots. I know it is a hassle but this time I was able to read the details.

    I see that you are trying to operate the headset in the Capless mode. This works fine with just a headphone but not with a headset that has a microphone. Here is how it works.

    The headphone output pins sit at the common mode voltage (CM) which is ~AVDD/2.

    So does the mono out pin and it has good drive capability so it can be used as a node sitting at CM voltage. So now the speakers will work with no capacitors. You wired the common of the headphone speakers to the Mono Out pin which is sitting at the CM voltage.

    Now here is the problem. The microphone also uses the same common connection in the headset that the speakers so. It is labeled ground on the sleeve of the jack. You connected it to Mono Out.

    So this is the way you are using the microphone, as a single ended mic.   Here is the diagram in the datasheet.

    So you connected the hot signal correctly to the cap and the other side of the PGA to CM.

    But, look at the current path for the MICBIAS power. It comes from the pin through the 2K resistor then to the microphone and then through the microphone to the mic's ground pin but that pin is now connected to the Mono Out which is sitting at the CM voltage!

    You have the MICBIAS register set to the default which is AVDD x 0.9. Most mics want to see around that voltage. But the MONO out pin is sitting at AVDD/2, otherwise stated as AVDD x 0.5. So this means you are running the microphone at AVDD x 0.4 V which is really low. This is why you have such a small output and lots of noise.

    You will have to ground reference the headset. I don't see a way around that. Which means you will need to have caps on the speaker connections and configure them as ground referenced. You did goon in that you have the option in your design. I see the caps as DNP. Give that a try and I think you will have better results.

     

    Dave T

  • Hi Dave,

    We have tried your suggestion and modified circuit as attached. But still we are getting noise in recorded audio. The noise has increased more now.

    We have tested the jack to IC pin path using sine wave and found no issue while the signal reaches the IC pin.

    Please let us know for further any changes.

    Regards,

    Anirudha