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In short, the sound card I have is behringer fca610. Then I have an Analog to digital converter. when I connect the ADC to the sound card, even if I do not turn on the audio, there is still noise, crackling. I connect via ODT Toslink.

Audio goes through the chain, but still a lot of noise.

Maybe you need to configure the asio buffer or sample rate. Or where there is so much noise, or you can’t insert the converter into the sound card. And you need to insert into the amplifier or av reviser?

By the way, the sample rate of the ADC is 48,000 hertz. And the output audio is LPCM

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    Why are you chaining DACs? I don't see the point. If your second un-named DAC is causing cracking, then it's probably the DAC. s/pdif doesn't have a clock, it's carried in the actual samples themselves so has to be re-clocked by the receiver. Your receiver is glitching.
    – Tetsujin
    Sep 8, 2019 at 15:23
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    Is the Behringer set to sync to external audio clock? It has to use the clock pulse coming from external ADC, or otherwise you'll get crackling. Even if both the ADC and the Behringer are set to the same clock rate, if there are multiple clocks, they're bound to run at slightly different speeds, and inevitably at some point in time, clock A has produced one more sample than clock B, and what do you do then. Throw away a sample? Insert an extra sample? Sep 8, 2019 at 18:24
  • Is this even possible? I have the cheapest converter. Like you can see on this page amazon.co.uk/slp/analogue-to-digital-converter/4xqnt9yxgacn65r Sep 9, 2019 at 7:40
  • When I change the synchronisation settings (or sample rate) of the fca 610 then I connect the converter, the sound does not pass. As if the converter freezes. And if I just turn on the audio card and connect the converter, the sound goes, but with a noise and not at 48khz but at 41,000. Attached a screenshot of the settings. What is there to choose? Sep 9, 2019 at 7:46
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    The Behringer should be set to sync to External Clock. If there is an external device sending digital audio that cannot sync to the Behringer's clock, then the Behringer must be "slave". There can only be exactly 1 master word clock in a digital audio network. When you connect two digital audio devices together, it creates a network. By the way, why are using such a cheap external ADC - is there some reason why you can't use the Behringer's analog inputs? Is the sound so bad that using an external ADC is worth the trouble? Sep 9, 2019 at 8:38

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The Behringer should be set to sync to External Clock. If there is an external device sending digital audio that cannot sync to the Behringer's clock, then the Behringer must be "slave". There can only be exactly 1 master word clock in a digital audio network. When you connect two digital audio devices together, it creates a network.

If clocks are not synchronized, you get crackles in the audio.

Here are a few randomly selected web articles that explain word clocks and synchronization in digital audio connections

https://en.wikipedia.org/wiki/Word_clock

https://www.soundonsound.com/techniques/does-your-studio-need-digital-master-clock

https://www.sweetwater.com/sweetcare/articles/what-digital-audio-synchronization-differ-time-code-synchronization/

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