[Another late reply -- Easter and taxes got in the way]
At 09:59 -0400 09-04-2009, Chris Mack / N1SKY wrote:
Imagine this: if you were the mastering engineer for Elvis 50 years
ago, and if today's digital technology was available back then, would
you want to archive the King's record inside Iron Mountain on MP3?
Not really, you would want the most resolution possible for the re-
release onto 32-bit 384kHz whiz-bang chip media in the future. And
cumulative error for successive re-releases over the decade for
frequency drift and re-archival is maybe another concern.
What cumulative errors are going to impact digital->digital transfers??
For example, I am currently using a Rosendahl Nanoclocks (http://
www.rosendahl-studiotechnik.com/nanoclocks.html) for my house master
word clock and a $6k Eventide Orville for processing of audio. The
Eventide used to measure the Nanoclocks at 88200 Hz... now it
measures 88201 Hz 4 years later... something drifted.... The
Rosendahl uses normal ambient crystals (although they have trimmer
caps) and use 74ACT00 logic to drive the distribution outputs. The
Eventide, I assume uses normal ambient crystals too for the myriad of
DSPs in it....
(What do you mean by 'ambient crystal'? AT cut with minimal df/dT at
room temperature?)
So your Nanoclock drifted relative to your Eventide. Even assuming
that the absolute frequency shift of your converter clock was this
much, that translates to a pitch shift of 0.02 cent. Find me *anyone*
who can hear that in an ABX test. For that matter, try finding a
string instrument that stays within 0.02 cent of its tuning after a
minute or two of playing.
[snip]
I believe Mr. Lavry for his 127dB ADC uses an OCXO which helps
achieve the specs. http://www.lavryengineering.com/
productspage_pro_ad122_96mk.html
The fact that one good converter uses an OCXO doesn't mean that you
have to use an OCXO to build a good converter. The Grimm one
mentioned by Chris C gets by just fine without one, for example.
JDB.
[plus, all things being equal an ovenized oscillator has higher
Johnson noise than one running at room temperature]
--
LART. 250 MIPS under one Watt. Free hardware design files.
http://www.lartmaker.nl/
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