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TLV320AIC3120EVM-U: Microphone Noise Gate Not Working

Scott Gaetjens
Intellectual 270 points
Part Number: TLV320AIC3120EVM-U
Other Parts Discussed in Thread: TLV320AIC3120

Hello,

I'm evaluating the TLV320AIC3120 for a voice amp application.  I'm writing 0x10 to register 0x1D (Decimal 29) to enable ADC to DAC loopback.  This works - I can hear my microphone being projected out through my connected speakers when I set the Analog Attenuation to -12.

My issue comes when I try to implement a noise gate using the AGC.  It never seems to activate.  Here are my settings:

With AGC enabled and my noise threshold set to -50, I still hear noise coming through my speakers.  When I gently rub the microphone (so I don't exceed the noise threshold), I can hear it coming through the speakers.

Am I doing something wrong or misunderstanding something about how the noise threshold works?

  • 0
    TI__Mastermind 30155 points

    Hi Scott,

    I think you're confusing Noise Threshold with Noise Gate. The Noise Threshold of the AGC is not a gate. It is the threshold at which the AGC kicks in, meaning that while the signal is below the threshold, the PGA is set to 0dB gain i.e. no extra attenuation. A noise gate would set the level to -inf, but since it controls the PGA, it would get stuck there and no signal would ever come through. 

    I hope this clears up the confusion,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Intellectual 270 points

    Thanks for that clarification, Jeff.  Is there a way to implement a noise gate on this part?  Not a big deal if it's not possible, but it would be nice if it could.

  • 0 in reply to Scott Gaetjens
    TI__Mastermind 30155 points

    Hi Scott,

    There isn't a dedicated gate available. You might be able to use the miniDSP to create your own gate, but I looked and didn't find a gate block already available. It wouldn't be very simple but I imagine it's possible.

    Best regards,
    Jeff McPherson