Stereocoder 38Khz multiplex not working on adau1451

Hi,

I build de stereocoder in adau1451 from the schema in adau1701. It works accept the 38Khz won't come out.

Did try to change the clock settings and sample rate but solves nothing.

Stereocoder-1701.dspprojstereocoder-1451.dspproj

  • 0
    •  Super User 
    on Oct 16, 2021 11:56 AM

         Hello,

         The ADAU1701 has buitt-in converters and can easily switch sample rates with no HW mods except perhaps the DAC output filters.  On the other hand, the -1451 needs an external codec to provide analog in and out -- and the codec sample rate is set separately.  What hardware are you running your project on?   If it's a stock eval board or anything that uses a AD codec in standalone mode, the DAC remains at 48K even when your 1451 project is at 192 K.  You'll need to run both the -1451 and the codec at 96K (or 192K if outputting both MPX sidebands).

         Best regards,

         Bob

  • Hi Bob,

    I am using a raspberry pi 3b with a hifiberry dac-dsp on top. Using the spdif input and the analog out by the dac pcm1502a.

    Am I understanding correctly that the spdif is interfering with input and output? because I don't use any codec yet.

    Can I test a setup without audio input, so that I can at least isolate the problem?

    Thanks in advance for your answer.

  • 0
    •  Super User 
    on Oct 16, 2021 8:58 PM in reply to BenM

         Hi Ben,

         Thank you for attaching your project as it makes clear what you're working on.  You can test without audio input by substituting oscillators.  The arrangement shown has both in-phase and out-of-phase signals so it should provide both baseband and MPX outputs.  Note that the VCO input voltage needs to be reduced 4x to get your 19K & 38K outputs at the 192K sample rate -- hopefully that's the only thing that's wrong!  If not it will take some more digging.

         The data sheet for the PCM5102A DAC shows that it can adapt via internal PLL to your 192K rate as long as hifiberry set it up that way (I think).  Do they show how to set up the -1451 clocks for 192K operation -- either in the docs that come with the board or on their support site?  I'm afraid I cannot help with the clocks because my 1452 eval board has its AD1938 DAC stuck in 48K standalone mode.  As soon as make any change to the Clock Gen1 settings the audio mutes, and I've learned (the hard way) not to suggest anything that hasn't been tested.

         Best regards,

         Bob

  • Hi Bob,

    I made your input working on the 1701 and the 1451. On the audio part its working but as you can see on the images the MPX shows up @ 10KC (mpx(wrong) 1451 and look @ the correct output from the 1701.

    1451 audio and output pilot 19KC and mpx 10KC Did also made a 38KC directly from a sine wave but outputs the same

    1701 audio and output pilot 19KC and mpx 38KC

    I

  • 0
    •  Super User 
    on Oct 17, 2021 5:18 PM in reply to BenM

         Hi,

         I like your analyzer readings!  In your project the MCLK setting calls for a 24.6 MHz crystal.  Most boards I've seen use a 12.288 MHz crystal, so if hifiberry employed a 12.288 MHz crystal on the board, change this setting.  The base Fs refers to whether it's 48K or 44.1K and does not concern the higher rates.

    You can also perform this test:  Make a copy of your project (so the copy project has the same HW settings).  Replace the MPX circuitry in the copy project with just one 20 kHz oscillator feeding the DAC output directly, then read this output with your analyzer.  If the output frequency is other than 20 kHz then your HW sample rate isn't 192K -- and thus your clock generator(s) are not set correctly.  The -1451's HW sample rate settings involve the PLL for the core clock which remains at about 295 MHz, so we don't need to change this.  But then a set of clock gens do the sample rate and other functions.  These confuse me, yet there's various threads on EZ which may help you get all this set correctly.  One of them is here.  Once you get your copy project to output 20 kHz, duplicate the new HW settings on your MPX project.

         If it still isn't working, hopefully a ADI SE will chime in during the work week.

         Best regards,

         Bob