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TLV320AIC3206: Why is my microphone so quiet and how do I adjust the gain correctly?

Part Number: TLV320AIC3206

Dear forum members,

I am using a TLV320AIC3206. While playback works flawlessly, the microphone volume is currently way too quiet to be usable. The quality seems fine. I was wondering whether my setup might be wrong or if there is any other issue. 

What is the correct procedure to identify the correct PGA/ADC values? I am not using the AGC just yet, since I wanted to get a decent sound without the AGC first and then set the desired value later. I am also using amixer instead of writing directly to the bus. The following controls are exported:

ADC Level Volume							
ADCFGA Left Mute Switch					
ADCFGA Right Mute Switch					
AGC Attack Time							
AGC Decay Time								
AGC Gain Hysteresis						
AGC Hysteresis								
AGC Left Switch							
AGC Max PGA								
AGC Noise Debounce							
AGC Noise Threshold						
AGC Right Switch							
AGC Signal Debounce						
AGC Target Level							
Auto-mute Switch							
CM_L to Left Mixer Negative Resistor		
CM_R to Right Mixer Negative Resistor		
HP DAC Playback Switch						
HP Driver Gain Volume						
HPL Output Mixer IN1_L Switch				
HPL Output Mixer L_DAC Switch				
HPR Output Mixer IN1_R Switch				
HPR Output Mixer R_DAC Switch				
IN1_L to Left Mixer Positive Resistor		
IN1_L to Right Mixer Negative Resistor	
IN1_R to Left Mixer Positive Resistor 	
IN1_R to Right Mixer Positive Resistor 
IN2_L to Left Mixer Positive Resistor		
IN2_L to Right Mixer Positive Resistor	
IN2_R to Left Mixer Negative Resistor		
IN2_R to Right Mixer Positive Resistor	
IN3_L to Left Mixer Positive Resistor		
IN3_L to Right Mixer Negative Resistor	
IN3_R to Left Mixer Negative Resistor		
IN3_R to Right Mixer Positive Resistor	
LO DAC Playback Switch						
LO Driver Gain Volume						
LOL Output Mixer L_DAC Switch				
LOR Output Mixer R_DAC Switch				
Mic PGA Switch 							
PCM Playback Volume 						
PGA Level Volume 							

I assume that the following controls are interesting in the first step:

  • ADC Level Volume
  • PGA Level Volume
  • Mic PGA Switch
  • IN1_R to Right Mixer Positive Resistor
  • IN1_R to Left Mixer Positive Resistor
  • CM_L to Left Mixer Negative Resistor
  • CM_R to Right Mixer Negative Resistor

Can someone confirm and give me hints regarding the best procedure to set this up correctly? 

Thank you for your help!

  • Hi Max,

    What's the voltage (rms) that you're sending to the input pin? With 0dB gain, full-scale is only .5Vrms. You were right to ignore the AGC for now since it is just automating the PGA. You should be able to program the PGA directly to a volume that's satisfactory. You can also use the ADC digital volume control.

    There really isn't a "procedure" to follow here other than ensuring that you are giving a sufficient voltage to the input pin and that your PGA and ADC level settings aren't so extreme that you're boosting too much noise.

    Best regards,
    Jeff McPherson

  • Hi Jeff,

    thank you for your fast response!

    I had a wrong resistor in a voltage divider, which resulted in a very low signal. I have since replaced it with a higher resistor, which now gives me .1V - .2V on regular regular speech. However, this does signal is ground centered. Is that a problem? Should I add a bias of .75V? 

    Not quite sure if changing the PGA does make a difference, it does not really sound like it. I was wondering if the above configuration is the reason for that. Furthermore, increasing the values for either the ADC or PGA  too much results in the recorded audio to disappear completely. Does it get clipped somehow, if the signal gets out of specs?

    Thank you for your input so far!

  • Hi Max,

    As long as you have AC coupled the signal so that the device's common mode voltage is separated from the source's common mode voltage, it's fine. Double check 11.2.2.1 in the datasheet.

    The PGA should definitely be affecting the sound as long as it's enabled and you're listening to the ADC path. It's hard to tell without you're exact register configuration. I'm not very familiar with amixer but we can loop our software expert in if needed. 

    As for the sound disappearing, you may be entering the reserved area of the PGA register. You should only go up to a gain setting that is documented in the register map. You can cause clipping if you turn the PGA volume up too high but I wouldn't expect the sound to disappear completely.

    Best regards,
    Jeff McPherson