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AIC3101 AGC noise gate threshold

Steven Weng1
Expert 2200 points

Hi All,

I tried to use AGC noise gate threshold for reducing background noise in mic input at speech situation.

But it seems not work...the following is my AGC configuration, hope someone could give me some suggestion.

Left Channel:

reg: 0x1a=0x8f (AGC enable, AGC target level=-5.5db, attack time = 20 ms, decay time = 500 ms)

reg: 0x1b=0x4c (AGC maximum gain=19db)

reg: 0x1c=0x38(clip stepping is disabled, AGC noise threshold=-84db, Hysteresis = 1 dB)

reg: 0x22=0x7f(Signal Detection Debounce=32ms, Noise Detection Debounce=448ms)

Right channel's configuration is the same.

reg: 0x1d=0x8f
reg: 0x1e=0x4c
reg: 0x1f=0x38
reg: 0x23=0x7f

I have some question:

1) Read ADC Flag Register(Reg36), it always 0x55(D5 AGC Signal Detection Status always 0) with or without speech.That means the noise signal power is greater than or equal to noise threshold? But I tried to unplug microphone from phone jack. So there should be no noise signal...but the flag is the same. Am I missing something?

2) Could someone please tell me how to configure the noise gate threshold for reducing background noise?

Thank in advance

BR

Steven

  • 0
    TI__Mastermind 28585 points

    Hi Steven,

    By setting the noise threshold so low (-85 dB) you will always have signal, even with no input. You need to try a larger number. You want to set the threshold just bellow the lowest expected mic level. Try -40 dB or so.

    Best Regards,

    dave

  • 0 in reply to Converter Apps
    Expert 2200 points

    Hi Dave,

    Thank you. The problem solved.

    There are three audio codecs connected on our board. The following is one audio path of our usecases.

                                                            ---------> codec 1 i2s record                               ----------> codec 2 i2s record

                                                            |                                                                         |

    Analog audio -> codec 1 mic input ----------> codec 1 line output -> codec 2 line in ----------> codec 2 line out

    When I enable codec 1 AGC, the noise from the codec 1 input will be filter and the record audio in codec 1 is clear!

    But the record audio and line out of codec 2 still have noise...there should be some noise source from codec 2 line in on our board. So After I enable codec 2 AGC, the noise is disappear.

    Thank for your help!

  • 0 in reply to Steven Weng1
    Expert 2200 points

    Hi Dave,

    Sorry about another question.

    As I know, AGC will auto adjust the PGA gain to achieve target output level. If the input signal is less then noise gate threshold, it could be as the PGA gain applied zero?

    In AGC, the analog input bypass path(PGA->output to line out) will be affect as PGA->ADC path?

    Thanks!

    BR

    Steven

  • 0 in reply to Steven Weng1
    Expert 2200 points

    Hi! 

    Could someone answer?

    background noise below the noise gate threshold will be remove or just un amplified?

    Are there same effect in the PGA bypass path and PGA to ADC path at AGC enabled?

    thank 

    BR

    Steven

  • 0 in reply to Steven Weng1
    TI__Mastermind 28585 points

    HI Steven,

    The analog bypass path will also be effected by the AGC gain.

    Best Regards,

    dave

  • 0 in reply to Steven Weng1
    TI__Mastermind 28585 points

    Hi Steven,

    When the input level is bellow the noise gate value, the output will be muted. It will unmute as soon as the input exceeds the noise gate value.

    Best Regards,

    dave

  • 0 in reply to Converter Apps
    Expert 2200 points

    Hi Dave,

    Thank you very much!

    When the input level is bellow the noise gate value, the output will be muted.

    The output will be muted that means the ADC output will be muted? So the noise gate threshold is useless in the analog bypass path?

    Sorry for many questions.

    Thanks again!

    BR,

    Steven