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USB clocking for 44.1k?
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Posted on March 2, 2017 at 17:43:49 | ||
Posts: 559
Joined: September 21, 2001 |
I like the idea of async USB, since the hi-fi DACs clock is usually better than a PCs clock. However, it seems that USB chips use 12MHz clock, which is not an integer multiple of 44.1kHz. So a 44.1kHz digital audio signal goes through USB (not S/PDIF, nor I2S), will there be some artifacts like those from asynchronous sample rate conversion? |
RE: USB clocking for 44.1k?, posted on March 4, 2017 at 11:12:25 | |
A DAC....you saw had those, not every Dac has the same number of clocks or the same Hz. |
RE: USB clocking for 44.1k?, posted on March 6, 2017 at 08:21:56 | |
Posts: 4209
Location: Somewhere nice on planet dirt Joined: September 25, 1999 |
Hi, > Interesting, it was my understanding that recording studios routinely > used one Master clock to sync everything. > > Maybe I misunderstood. Maybe, instead of trying to understand how such systems work, you merely took away what you wanted and ignored most? You cannot slave/sync the USB (or Wifi, or Ethernet etc. etc.) Clock directly to studio clocks, for the simple reason that the clock frequency is wrong. The job of the "House Clock" is to synchronise the audio (and often video clocks) of multiple converters, so that multiple devices do not loose "sync". You can see the need when handling Video & Audio using separate converters. I think you can also appreciate the need if we (say) use three stereo ADC's to make a six channel recording. Each individual Quarz Crystal in a given oscillator will have a frequency that is just a tiny bit different. So if we wait long enough, they will no longer be synchronised. So while the need to synchronise clocks is obvious, there is a dirty little secret in that. Most Pro-Audio devices perform notably worse on external clocks, than when running on cheap internal crystals. And of course on top of that any non-audio clock in the system (e.g. USB, Ethernet etc.) will not be synchronised to the audio clock. You may find this article useful on the studio perspective: http://www.soundonsound.com/techniques/does-your-studio-need-digital-master-clock Thor At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need? |
Ahhhh Great Info THANKS!!!nt, posted on March 6, 2017 at 08:32:26 | |
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RE: USB clocking for 44.1k?, posted on March 6, 2017 at 08:42:21 | |
Posts: 4209
Location: Somewhere nice on planet dirt Joined: September 25, 1999 |
Hi, > Not Feasible?? Not really. You can sync the audio clocks, but Async USB operates the audio section from a local clock anyway and the USB clock is needed for the USB operation and not directly linked to the audio side. It probably is worthwhile for you to truly understand how Asynchronous USB works and what the implications are. This article may be of help: http://www.edn.com/design/consumer/4376143/Fundamentals-of-USB-Audio Thor At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need? |