[cma-l] Audio crackling

Two Lochs Radio tlr at gairloch.co.uk
Mon Oct 31 13:10:01 GMT 2011 

Okay, no that doesn't sound like a buffer problem at all.

If the crackle continues during silent passages i would say it is a hardware problem, most probably a power supply filtering issue. (It could be, for example, a dried out electrolytic capacitor that cease to perform sufficient filtering as it gets a bit warmer.)

If the crackling disappears or changes greatly during silent passages, which it sounds like it does, I would say it was more likely a software problem. It does change a little as the sound gets louder, but this could happen as power loading changes with the volume.

It could also be a 'rectifying contact' - usually a dirty or tarnished one, or a cracked resistor among many posibilities.

There is very distinct almost continuous series of spikes at 204Hz (4.88ms period) which ought to give a clue, but doesn't immediately ring any bells, so to speak. 

If it is software, it might be something happening at high speed, for example if you are using the card to perform a sampling rate conversion (eg 44.1kHz to 48kHz), and it is failing to keep up with the pace, that could possibly produce crackle effects.

I don't think your hard drive is implicated, but it is possible that the crackle is a manifestation some data issues where the data is passing at a high rate beween the drive and the system - maybe a problem with DMA interrupts/speed of access, but my gut feel is that is not the most likely cause - it does sound more like audio hardware/power problems to me (as i stab in the dark!).

Alex
  ----- Original Message ----- 
  From: London Chinese Radio 
  To: Two Lochs Radio ; Tony Bailey 
  Cc: CMA-L 
  Sent: Monday, October 31, 2011 12:48 PM
  Subject: Re: [cma-l] Audio crackling


  Hi,

  Here is a sample of the audio. As you can see, it's pretty bad!
  It doesn't solve it by disconnecting and reconnecting the audio stream. But it does sound very software-y.

  The HD is an old IDE drive, but the motherboard, which has mostly SATA ports on it, had an IDE port, so I installed it. So it could be that...   I'm not properly trained, only find out things by overcoming problems like this...!

  Anyway, I am attaching a small sample from the stream... 


  Peter





  2011/10/31 Two Lochs Radio <tlr at gairloch.co.uk>

    Does the crackle stop for a while if you stop and restart the audio stream? If so, that would suggest a small bite rate mismatch is not being properly handled and is resulting in repeated buffer overflows, which depending on how well the software handles dumping the excess data can sound like a crackle or a 'glitch'.

    But the description 'crackle' can cover a multitude of effects. is it possible for you to post a little audio sample of it somewhere we can access (or email me a small pice directly if you want) in case the actual sound triggers any other thoughts.

    Alex

      ----- Original Message ----- 
      From: London Chinese Radio 
      To: CMA-L 
      Sent: Monday, October 31, 2011 10:41 AM
      Subject: [cma-l] Audio crackling


      Hi,

      I wonder if anyone has had problems with audio crackling? 
      I have recently changed to a different streaming PC, (because it was XP, and I had a Marian marc8 midi sound card which has 8 ins and outs, but doesn't support Win7), and it was fine for about a month, until it started crackling. I put all the audio on a seperate HD, and because they are quite close together, I also fitted a large fan next to them, which delivers quite an icy blast across the disks.
      It starts crackling after a few hours, and it ruins the stream. It is solvable by rebooting. I originally thought it could be something overheating, but since it is solved by rebooting, without the time for anything to cool down, I don't think that is it. 

      System info: 

      Airmate out into Soundcard in (channels 1 & 2)
      mAirlist (6 Channels) and computer audio (2 channels) via Soundcard outs into Airmate channels
      Asus P5K-VM motherboard with an Intel Core2 duo CPU. (it's a Red Sub computer with a few extra things I've added)  
      The CPU cooler is a bog standard one but with a funnel that directs the hot air out of a vent on the side. 

      Anyway, if you have an idea, I'd really appreciate any advice. 


      Peter Vautier
      London Chinese Radio
      -- 

      野火烧不尽，春风吹又生




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  -- 

  野火烧不尽，春风吹又生

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