Re: Timing problem on PPC based Macs (PortAudio)
Re: Timing problem on PPC based Macs (PortAudio)
- Subject: Re: Timing problem on PPC based Macs (PortAudio)
- From: Ethan Funk <email@hidden>
- Date: Sat, 21 Mar 2009 07:33:59 -0700
How does a modern Mac's CPU timebase accuracy compare against a
mid- price digital audio device's samplerate accuracy?
Would there be reason to expect that a Mac Pro's UpTime or
mach_absolute_time nanosecond measurement would be more long-term-
accurate, less long-term-acurate, or about the same long-term
accuracy compared to a nice mid-price audio interface like a MOTU
2408mk3?
I don't know how they compare, but one factor to consider is that
often these machines use NTP to synchronise their time APIs to a
network time base -- afaik the synchronisation algorithms calibrate
correction factors for the local clock rate vs. a network standard
time base, and this can become "pretty accurate" over time. I'm not
sure how tempurature affects things though.
Ross.
From a hardware stand point, everything except very high end
equipment, including computers, uses quartz crystals as the resonant
element in the time base oscillator. The frequency tolerance of a
typical quartz crystal is in the range of 20 to 100 ppm (parts per
million), and about 30 ppm drift over reasonable temperatures. So
the WORST case (extreme temperature difference included ) error
between two device clocks should not be more that 260 ppm, or aprox.
0.03% 100 ppm would be a realistic error to expect.
Ethan...
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