[time-nuts] FEI-5660 Rubidium Oscillator

Chris Albertson albertson.chris at gmail.com
Thu Mar 27 21:24:34 EDT 2014

The audio marketplace is really weird.   For many the goals is not sound
quality but bragging rights "I spent more money then you did." or "My ears
are so good I can hear if a cable as been swapped end for end."   Some even
think they can hear the difference between gold and nickel pated AC mains
power plugs.

There is one good reason for long-term stable frequency reference in audio,
it's not in home playback equipment but in recording.  You like two one
hour recordings that have the same duration to also have EXACTLY the same
number of samples.  I've seen errors where two recorders where running
independently and later when played back using a common clock they got out
of sync because one had a very slightly different sample rate.  This is no
different then in the analog recording world if one tape machine is faster.
 They fixed this by using multi-track machines up to about 24 audio tracks

Rubidium makes some sense because tracks recored weeks apart and/or a
continent apart can then be exactly sample per sample in sync.

But for home use in playback.  It's like gold plated speaker wires, just
taking the "mark's" money.

On Thu, Mar 27, 2014 at 4:10 PM, Tom Van Baak <tvb at leapsecond.com> wrote:

> > Recently I happened across an eBay listing for an Antelope Audio
> Isochrome,
> > a device that apparently packages an SRI-PRS10 rubidium oscillator and
> > distribution amplifier in a box and sells to audiophiles for a price in
> the
> Bruce,
> There have been threads about this on time-nuts every few years. The
> consensus is that audio companies that use atomic clocks are naive. It
> makes good marketing, though.
> Then again, speaking from experience, many of us make the same mistake:
> first thinking that precise time is the goal, then thinking that precise
> frequency is what counts, and later thinking that stability is what really
> matters, and only eventually realizing that all of these metrics are
> functions of tau, and that tau ranges from MHz/microseconds to years. Phase
> noise plots along with log-log ADEV plots start to tell the whole story.
> In the case of digital music, as far as I know, L(f) phase noise in the
> audio band and ADEV(tau) frequency stability from microseconds to seconds
> is far more important to the fidelity of digital recording and playback
> than absolute SI-accurate frequency or long-term timekeeping. Consequently,
> most atomic frequency standards are actually a poor choice as a sampling
> reference clock -- because their jitter (short-term noise) is no where near
> as good as a free-running, undisciplined, high-end OCXO.
> True, the PRS10 is a better choice than other cheap telecom rubidium's but
> none of these comes close to the performance of a premium OCXO. For the
> ultimate audio reference clock you want to avoid Rb, or GPSDO, or Cs for
> that matter. Instead pick a 1e-12 or 1e-13 stable OCXO, strap it to a 100
> pound block of granite, and leave it alone.
> /tvb
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Chris Albertson
Redondo Beach, California

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