[time-nuts] from Sputnik to CD

[Magnus Danielson]

From: "Tom Van Baak" <tvb at LeapSecond.com>
Subject: Re: [time-nuts] from Sputnik to CD
Date: Fri, 5 Oct 2007 17:46:46 -0700
Message-ID: <000701c807b2$5fe363d0$0800a8c0 at pc52>

Tom,

(or is that Tom-Tom?)

> > OK, not really a time related post...except for the clock in the CD 
> > player...which begs the question, any time nuts play with creating a 
> > more precise CD player using a precision oscillator?  Think it would 
> > make a difference?  I can see the selling point now "Our CD player is 
> > Rubidium controlled!"
> > 
> > Tom Frank
> 
> Tom,
> 
> The question, as if often the case with matters of timekeeping,
> is do you want a precise CD player or a stable CD player?
> 
> The link about CD mastering and Rubidium clocks is:
> http://www.rogernichols.com/EQ/EQ_95-09t.html
> I thought some years ago there was a separate web page
> about his atomic CD mastering system; can't find it now.
> 
> I tried to contact him about his this but never connected. As
> far as I can tell he misses the point; atomic clocks (at least
> Rubidium) are not known for their superb short-term stability.
> Here is where high-end SC- or BVA- quartz is still supreme,
> sometimes 10x to 100x over a typical Rb.
> 
> I'm not an "audiophile" bit it seems to me that phase noise, or
> milli- and microsecond adev, is the critical parameter. A spec
> like long-term stability, such as what you get with an Rb or Cs
> or GPSDO frequency reference, is mostly irrelevant to the
> fidelity of sound reproduction.
> 
> If the sample rate is 44.1 kHz then the adev below 1 s, even
> down to 10 us, or jitter, or the phase noise above 1 kHz are
> they key parameters; not long-term drift. In this case I'd take
> a nice 10811A over a typical Rb any day. Does anyone know
> for sure, or am I off base here?

No, I meant to say the same. The phase-noise in the 10-1000 Hz region is
surely what will mostly affect the sound, so we are looking at side-band
phase-noise rather than Allan dev plots. However, slow modulations even up to
a minute is known to be perceptible, but the tolerance levels is not flat.

But even for taus of 100 s I think a good OCXO such as the 10811 outperforms
any Rb and especially for the money.

If anyone is interested in learning about serious reasoning behind acheiving
high dynamic digital audio, look up Julian Dunn, who has written a few very
good papers. He also did work for the AES/EBU jitter limits and also wrote some
stuff for Audio Precision. Great stuff and a sensible reasoning on these
things.

It should be noted that for lower modulation frequencies, the side-band will
be so near that the ears masking-effect will cancel it out unless it is
strong, so tolerance levels rises for lower frequencies.

Cheers,
Magnus