• Registered: 2013-05-02
  • Posts: 2

Topic: HDSPe MADI on Linux, doesn't get enough sample

Hi everyone,

I'm using HDSPe MADI on Linux setup for recording streaming audio to wave file. It's serving it's basic purpose just fine, we are able to create audio wave recording in 1 hour chunks.

But now we discovered that we don't actually end up with exact 48 kHz sample per second. When you play the files that suppose to read as 1 hour, it only registers as, say, 59m 58s. We ran some tests and we found out that it's missing a few microseconds with each samples.

Any hint what could we be missing? I heard something about time synchronization, or even using external clocks. Could this be the case? Can you give some ideas what I can try?

Thanks a lot!

2 Reply by MC

  • MC
  • MC
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  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 25,615

Re: HDSPe MADI on Linux, doesn't get enough sample

2 seconds deviation in 1 hour = 2/3600 = 0.000555 s deviation per second = 0.055 % = 55 ppm. That is a bit too much. The internal quartz of the card should give +-10 ppm. You are using the HDSPe MADI, where the internal clock can be freely adjusted to any value (SteadyClock, Pitch function). Most probably that value is set incorrectly in your Linux driver.

That said I doubt that the difference of 2 seconds has any meaning in real-world usage. You can also clock the card externaly to whatever source for playback and have it running for 2 hours or 2 hours plus 10 seconds or whatever, and you won't notice the small amount of audio pitch shitfting happening then.

Regards
Matthias Carstens
RME

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