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TLV320AIC3104: Setting a fixed PGA gain level, without using AGC

Chris Fernandez1
Prodigy 50 points
Part Number: TLV320AIC3104

For my application, I am digitizing an audio signal and handing it to my company's custom software application, which handles audio leveling.

Is it possible to set a static amount of PGA gain without having the AGC engine adjust the PGA gain automatically? Like a constant +3dB or +20dB of gain? I do not want the AGC to constantly change the gain to reach some target output level. How can I control the PGA level directly?

I have experimented with having the AGC register disabled (Registers 26/29), and adjusting the PGA level from 0dB to +59dB (Register 15/16). But this did not have any impact on the volume of my recorded .WAV file. However, if I enable AGC, then I observe a significant increase in .WAV volume, and I can see the AGC gain increase as expected when I view the .WAV file in Audacity. Note that I am using the tlvaudioCODEC driver from the Linux tree.

How can I manually apply a fixed PGA gain, without using AGC?

Thanks,
     -Chris

  • 0
    TI__Mastermind 40475 points

    Hi Chris,

    Yes the PGA is fully controllable in a discrete manner. It should be as simple as changing Register 15/16. Can you share your set up script so I can see if something might be conflicting?

    Best regards,
    Jeff McPherson

  • 0 in reply to Jeff McPherson
    Prodigy 50 points

    Hi Jeff, 

    Sorry for the late reply. I'm not using a discrete setup script, I am using the snd-soc-tlv320aic3x driver in the Linux kernel.

    This driver sets up an Alsamixer control to change PGA gain by writing to Registers 15/16. However, it writes the same value to BOTH registers - there doesn't appear to be an option for individual control over the left and right PGA gain.

    Additionally, this driver sets bit 7 High when writing to Registers 15 and 16, which enables Mute. So no audio is recorded in the resulting .WAV file - the samples are all zeroes.

    Is there another way to implement the kernel driver to allow individual control over these registers?

         -Chris

  • 0 in reply to Chris Fernandez1
    TI__Mastermind 40475 points

    Hi Chris,

    Understood. Let me loop in our driver support team to address your findings.

    Best,
    Jeff McPherson 

  • 0 in reply to Chris Fernandez1
    TI__Intellectual 2550 points

    Hi Chris,

    Sorry for the late response, In the kcontrols, the volumes of the two channels are indeed configured together as below, but volume and switch controls are individual, you can set switch control to record audio.

    Original code:

            /* Input */
            SOC_DOUBLE_R_TLV("PGA Capture Volume", LADC_VOL, RADC_VOL,
                             0, 119, 0, adc_tlv),
            SOC_DOUBLE_R("PGA Capture Switch", LADC_VOL, RADC_VOL, 7, 0x01, 1),

    We can do some small changes in above code to configure two registers separately, just like below:

    Modified code:

            /* Input */
            SOC_SINGLE_TLV("PGA Capture Left Volume", LADC_VOL,
                             0, 119, 0, adc_tlv),
            SOC_SINGLE_TLV("PGA Capture Right Volume", RADC_VOL,
                             0, 119, 0, adc_tlv),                      
            SOC_SINGLE("PGA Capture Left Switch", LADC_VOL, 7, 0x01, 1),
            SOC_SINGLE("PGA Capture Right Switch", RADC_VOL, 7, 0x01, 1),
    Kindly check the changes and do let me know if it can work for your system.
     
    Thanks