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Using TLV320AIC3254 for stereo audio volume control before mixing

Nimesh Shah
Prodigy 60 points
Other Parts Discussed in Thread: TLV320AIC3254, PCM3168A

Hi,

I am using TLV320AIC3254 audio converter. I have two stereo audio inputs which needs to be mixed as:  X% of 1st input and (100 - X)% of 2nd input. As in the datasheet, I figured out that the audio inputs are mixed first and then gain control works on the mixed source. And there is no such provision to control the gain of the inputs before mixing.

So is there any way to mix two stereo audio with different volume gains, without affecting the stereo effect?

Thanks,

Nimesh Shah

  • 0
    TI__Guru**** 189401 points

    Hi, Nimesh,

    I have asked my colleague to help you with this.

    -d2

  • 0
    TI__Expert 6715 points

    Hi Nimesh,

    For the headphone output, you can directly route the left and right channels from IN1 if you don't need any miniDSP proccesing on one of the lines being mixed

    What is your system trying to do? Which output are you going to? What kind of signals are you mixing?

    There may be other ways as well, but I will need some more information about your system.

    Regards,

    ~John

  • 0 in reply to John Fedak
    Prodigy 60 points

    Hi John,

    First of all, Thanks for the reply.

    I have two Stereo audio inputs IN1 and IN2 at the same time, implying 2 left channels and 2 right channels. My requirement is to mix x% of IN1 with (100 - x)% of IN2, applying for both the left and right channels and route the mixed audio to the Line-Out outputs. The audio inputs used are single-ended.

    Please ask if more information needed.

    Regards,

    Nimesh Shah

  • 0 in reply to Nimesh Shah
    TI__Expert 6715 points

    Hi Nimesh,

    Unfortunately, because there is only 1 ADC on each channel inside the AIC3254, this has to be done outside of the chip if you are mixing to audio signals. You could use an audio op amp to increase the strength of one of the signals, but it would not be changeable on the fly.  Without knowing anything else about the system, you could use a PCM3168A instead of the AIC3254 and that would give full control of mixing many different audio signals.

    Regards,

    ~John

  • 0 in reply to John Fedak
    Prodigy 60 points

    Hi John,

    Sorry for delayed reply.

    Thanks for the information. I reviewed the datasheet of PCM3168A available on the TI page, but was unable to conclude whether it will be able to mix the stereo audio inputs in the required proportion and out the mixed audio to the line-out output. Is there any 'Application Reference Manual' or some other document which gives more details regarding its applications so that our use-case gets covered in it?

    Regards,

    Nimesh Shah

  • 0 in reply to Nimesh Shah
    TI__Expert 6715 points

    Hi Nimesh,

    Unfortunately, there is no Application Reference Manual like the AIC3254. However, after re-viewing the d/s, I don't think it will work in your situation as it doesn't mix the channels, it can just attenuate for its own dedicated output. My appologies for the mis-recommendation.

    There is actually a simple solution to this if it is a fixed percentage. Are you looking to change the values on the fly?

    You can setup a resistor divider in front of the AIC3254 input and change the input resistor values to get different levels on each of the inputs. For reference a micPGA of 0dB and a 10k input resistor has an effective 15k to ground. You will want to keep the resistor values around 1k to avoid creating noise on the line.

    Regards,

    ~John