Computer Audio Asylum

Posted by KeithC (A) on April 18, 2007 at 11:34:43

In Reply to: Limited right now, just put the damn computer on the rack, best anyways. posted by Gordon Rankin on April 18, 2007 at 06:50:02:

I have two USB extenders - an optical one - expensive, and doesn't like USB audio - you are correct about the supplied psu, but even with a better quality one it still drops out at the device level.

T'other is USB -> RJ45 to USB. No psu, decent quality, I run it with a 10m Cat 5 interconnect into a HagUSB, but the spec states a maximum of 50m. And it cost approx. 25% of the optical extender.

BTW, OS X Core Audio software defaults the Mac Mini optical output to 44.1K, and the USB to 48K. All audio is converted to linear PCM (32 bit) for HAL interfacing.

• Core audio what....... - Gordon Rankin 13:53:00 04/18/07 (2)
  In Reply to: Re: Limited right now, just put the damn computer on the rack, best anyways. posted by KeithC on April 18, 2007 at 11:34:43:

  Keith,

  What are you smoken... All the ports are setup for whatever the Fs rate is. The optical defaults to 44.1 and so does the USB. This of course would differ if you are using a device driver for your usb.

  Also the USB only sends the data it is suppose too. In my code for my USB controller I specify 16 bit data and it comes down that way and then I can either send it out I2S in any form I want. The controller on the dac side pads to 32 bits. I set my buffers for what ever I want and go from there.

  I got a USB Analyzer and look at the data all the time if you want me to post it I can.
  Thanks
  Gordon
  J. Gordon Rankin
  
  

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  • Re: Core audio what....... - KeithC 14:21:03 04/18/07 (1)
    In Reply to: Core audio what....... posted by Gordon Rankin on April 18, 2007 at 13:53:00:

    I started with Cog console diagnostics (most third party audio players are based on the Core Audio sdk), confirmed by reading Core Audio documentation, and proved by connecting a DAC with rate display & relay switching.

    If you use your own software and bypass HAL this may not be the case - MplayerOSX does identify & handle the audio i/f correctly.
    
    

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    • Re: Core audio what....... - Gordon Rankin 14:35:36 04/18/07 (0)
      In Reply to: Re: Core audio what....... posted by KeithC on April 18, 2007 at 14:21:03:

      Keith,

      Do remember that with the USB driver does change the characteristics of the stream to match the enumeration of the USB device. In most cases this means clipping the 32 bits to whatever the enumeration is set too 8, 16, 18, 20, 24 or 32. The enumeration cannot be overridden. You set the device type (USB Audio 1.1 etc) the output width (bit size), max buffer length per packet and the rates you support.

      Basically my setup is simple. I plug in one of my USB DAC's were I programed the USB controller as above. My USB analyzer is connected in line and my DSO is connected to the DAC. With iTunes or what ever on the mac, sometimes Faber Audio Suites test or on the PC with Dr. Jordan or my Prism dScope III and test the unit.

      I have never had a USB device on a mac come up with anything other than 44.1K.

      Thanks
      Gordon
      
      J. Gordon Rankin
      
      

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