Audio into ADV7842/ADV7511 evaluation board

The last hurdle is audio. Can you tell me how to bring audio into the ADV7842/ADV7511 evaluation board?

 Requirements are:-

  1) to digitize anlogue stereo audio (RCA connections and leads to i2s for input to the 7511.
  2) to record the analogue audio at up to at least 96khz/24 bit and 192khz/24bit if possible

  3) to convert digital optical audio (s/pdif) to I2S for input into the 7511. The source for this will be my laserdisc player which has an optical out connection. This in turn depends on whether I elect to use the laserdiscs analogue or digital audio channels and output connections. These channels are selectable from the laserdisc players remote. I have yet to decide on whether i want to use analogue or digital from my laserdisks.      

I have investigated i2s and it looks like there are problems with it on PCB to PCB conncetions. I am interested to hear what you say on this.

I have looked over your ADAU1761 chip - its a DAC as well as an ADC. I am just looking into DACs. Shall look into your ADAU1761 further.

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  • Video - FYI only

    This is according to information i  have obtained from  the internet.

    VHS cassettes - on these both the audio and video on these are stored  as analogue. Further the video is stored as Y&C, ie s-video. To me this means that the  the better the bit depth of the digital converter, to a point, the better the final digital capture and final TV  display. Someones opinion on the internet  says that VHS video was about 10 bit, just their opinion,  so possibly at 12 bit capture rate  there could be only 2 bits in excess of requirements.  However  if capture programming is correct then these 2 bits should have a value of binary zeroes anyway precapture and should remain so after capture. Or does capture work some other way?

    Whatever, these are the lines i am thinking along.

     Digital conversion only takes place on VHS players when the internal TBC and DNR are used and these both, as i understand it, use A-D-A conversions. The internal TBC+DNR are very good for TV display but for digital capture i will have to  test to see whether they can be dispensed with and use computer  software to replace use of the internal TBC+DNR. This will have the benefit of removing  those domain conversions from the capture, which should help improve the captured file a little bit.  Most likely the TBC+DNR A-D-A conversions are 8 bit but i have no information on this.
    Hopefully the VHS player does not process the s-video signal much, or the audio signal, and what is output at the ports is pretty much as whats on the VHS cassette (apart from TBC+DNR use of course).            

    Audio - needs your input

    Thanks for the liinks - i have looked these over.

    I am going to need your guidance here.  Your ADC audio chips look like a minefield for the uninitiated.

    Can you update me on i2s inter-PCB board connections? How are these connections made from one PCB board to another? In my case this will be from an audio PCB  board to your 7842/7511 evaluation board j4 header i2s input connections for combining into the 7511  output HDMI signal.
    Can you please explain more about how inter-PCB board I2S connections are made? The i2s connection is a concern due to what i have read about these connections. Internet information shows that 3, at least, maybe 5, of the i2s output connection cables need the same impedance or equal lengths of cable for connections to the receiving device or there could be synchronisation problems. Hence the reason I want to clear up how this inter-PCB board connection is made even before i think about the ADC audio chip i need to use.  

    Your ADC audio chips that i have looked at are the AD1871 and the AD1974. The AD1974 looks interesting as it has a 192khz sampling option. Also the ad2428w looked very interesting as the datasheet talked about i2s output but i couldn't understand much on its datasheet especially its outputs.

    I am disreguarding my DAC requirements at the moment but your ADAU1761 chip, with ADC and DAC facilities, is still very interesting. A combined DAC + ADC  approach may reduce external cabling and connection requirements and so simplify connectivity.      


  • 0
    •  Analog Employees 
    •  Super User 
    on Sep 10, 2021 4:20 AM in reply to RagTag

    1) VCR players will output audio in a analog format with maybe a equivalent 10-12 bit accuracy.  When capturing a 10-bit source with a 12-bit ADC, the lower 2 bits will be noise, not zero.  Our converters start a 16-bit and go up from there.  This is the same issue we talked about before, if the video is only 24bits per pixel, why go to 36 bits per pixel.  You can use streams with the extra bits but the extra bits are going to be noise or extrapolated data

    2) FYI Video and audio streams do not have to be 100% in sync.  You will not detect any sync mismatch if it's less then 16ms, one 60 Hz frame.  

    3) I2S only needs to be a 3 fly wire connection from board to board, CLK, WCLK and one DATA line.  The data will carry stereo or up to 8 channels (TDM8).  Both boards will have headers that you can connect the I2S bus to.  For testing using different eval boards, this should be fine.  If you look at the 7842-7511 I sent before you will find the 7511's SCLK, LRCLK and I2S0 pins go to a header where the fly wires would connect to.

    4) The ADAU1761 is able to capture and play audio at the same time.  I've attached how I'm using it.  PDF

    I think I linked the wrong page, check this out

    Almost any part on that link link will do,  Maybe the ADAU1361.  ADAU1401 if you really must have 192kHz sampling rate.  Even though a chip has more features then you want or need, you don't have to use them all.

    5) The AD2428W is a automotive A2B to I2S bridge chip.  Not what you are looking for.

  • Thanks for that last reply and the new links.  I think that we are now getting there.

    I have had a quick look at your ADAU1761 implementation and i really need to study it further.

    I had a look at your parametrics webpage. The ADAU1401A and the new ADAU1850 chips have caught my attention. Are these chips for me or am i looking at the wrong items?

    I do want the option of recording at 192khz available should i wish to use it (or at least give me something to play with). I also like the idea that both these chips include both ADC and DAC functions which may help to reduce external cabling requirements.

    I need some guidance of the differences between the ADUA1401A and the ADUA1850. The ADUA1850 is looking very good to me.

    The ADUA1850 has:-
                                              1) an evaluation board available
                                              2) 3 ADC input  - i am going to need more of these than DACs
                                              3) an almost unrestricted sampling rate.
                                              4) a computer program to run it and easily connect by USB.

    Question - does the ADAU1850 output i2s?     

    Will either of these chips solve my very last concern which is about the conversion of a optical (and cable)  digital (SPDIF?) signal from either my laserdisc player or TV into:-
                                             1) i2s - for inclusion with the 7511 HDMI output signal for TV display and PC capture.
                                                1.1)  Is this possible? I cannot see it from the datasheets.
                                                1.2)  Or is another chip required somewhere?

                                             2) analogue - for input into my hifi stero amplifier.  

    Finally the DAC input connections - are they cable or optical? The digital audio outputs from my TV and  laserdisc player are optical.    

    From what you have said it looks like there are no problems with I2S inter-PCB board connections so my concerns here  have gone away. I should be able to handle these.

    If i am heading in the wrong direction on anything let me know.  


  • +1
    •  Analog Employees 
    •  Super User 
    on Sep 14, 2021 12:24 AM in reply to RagTag

    1) both chips will do I2S

    2) If you really need SPDIF then the ADAU1442 or ADAU1466 have SPDIF interfaces.

    These are more complicated.  I'm working on the ADA1472 right, way over kill for what you need.

    3) DAC will have analog outputs with buffers to drive headphones or other line level devices.  Normally the DAC are driven by the internal audio stream.  Any of these chips have internal matrix arrays which can route the audio anyway you want and DSP functions to process the audio on the fly.

    4) SPDIF requires a special interface beyond just a normal I2S port.   The 7511 only works with I2S inputs.

    5) I've used the ADAU1442 before.  It has the features you are looking for, a good eval board programmed via SigmaStudio.  Check out the user guide.

    If you need SPDIF you might consider this.