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[ADV7482] About audio mute when changing Audio sampling frequency

Category: Software

Hi,

I have some questions about MUTE.

Q1) Does the ADV7482 automatically mute the 2-channel L-PCM audio stream

       if the Audio sampling frequency of the HDMI input device changes?

       My understanding is as follows. Is this correct?

       When the Audio sampling frequency of the HDMI input device changes,

       the n parameter and cts parameter of the ACR packet received by the ADV7482 change, and the Audio DPLL is unlocked.

       Therefore, audio mute occurs.

Q2) Also, is it possible to send an interrupt notification (INTRQ output) when audio mute occurs?

Q3) Does the ADV7482 take any action on the HDMI input device

       if the Audio sampling frequency of the HDMI input device changes?

       Will audio and video stop during this time?

Best regards.

  • Hi,

    I'm sorry, but I have an additional question.

    Q4) The answer to Q1 is assumed to be' YES', how long does it take for

           the Audio PLL to unlock after receiving the changed Audio sampling frequency?

    I would be grateful if you could answer as soon as possible together with Q1 to Q3.

    Best regards.

  • Hi Tatsuya San,

            Please find the below comments,

    Q1) Does the ADV7482 automatically mute the 2-channel L-PCM audio stream ?

            ADV748x integrates an advanced audio mute function So ADV748x can be configured automatically to mute a 2-channel L-PCM audio stream but audio muting related register is need to configure as per section 5.3.17.1 (Audio Mute Configuration).

          Kindly note, We can configure the corresponding mute related register as per table 35  in ADV7482 Hardware Manual (Page 116).

          Also audio mute occurs, if ACR packets are not received within one VSync .

      Q2) Also, is it possible to send an interrupt notification (INTRQ output) when audio mute occurs?

                       Yes, Interrupt notification related register for audio mute is available. Please refer below snap for reference.

      Q3) Does the ADV7482 take any action on the HDMI input device. 

            if the Audio sampling frequency of the HDMI input device changes?

             Will audio and video stop during this time?

                  When there is change in audio sampling frequency, mostly we will be in mute state to remove all extraneous noise and pops from a 2-channel LPCM audio stream when switching from different sampling frequencies upto 192 kHz .

                  So during the mute condition the output data becomes 0 (= mute) - i.e It is silent data.

    Thanks,

    Poornima

  • Hi,

    Thank you for your reply.

    I would be grateful if you could answer about Q4 as well.

    I would like to confirm one point about Q3.

    Does changing the Audio sampling frequency affect the video data?

    Is it correct to understand that the audio is muted and the video is output?

    Best regards.

  • Hi Tatsuya San,

           Please find the below comments,      

    The answer to Q1 is assumed to be' YES', how long does it take for the Audio PLL to unlock after receiving the changed Audio sampling frequency ?

              Generally any disturbances to the HDMI signal can cause a loss of lock, for example change in frequency, loss of clock, change in transmitted N values but we don't know about the exact unlock time.

    Does changing the Audio sampling frequency affect the video data ?

       No, It will not affect the video data.

    Is it correct to understand that the audio is muted and the video is output ?

       YES.

    Thanks,

    Poornima