[time-nuts] Re: Accuracy of a sound card

[Chuck Harris]

Hi Poul,

I am quite aware that making a soundcard more accurate is gilding the
lilly.

But if you return to the middle of this thread, where I offered powerline
noise up as a reasonably accurate, ubiquitious timing reference, and had
my suggestion refuted by a gentleman with a soundcard based spectrum
analyzer, you would understand my point.

If you are going to use a soundcard as the basis for a spectrum analyzer,
and you are going to let your software readout 5 or 6 significant digits,
you are going to have to also realize that the oscillator in the sound card
is not very good, and your data is suspicious.

In an effort to illustrate this point, TVB made a graph of the characteristics
of his high quality sound card, and low and behold, it behaves just like it has an
uncompensated crystal oscillator...imagine!

There are no adjustments of any kind on these boards, let alone any for
frequency.  There is no reason to believe that they will be any more accurate
than musicality requires.

-Chuck

Poul-Henning Kamp wrote:
> In message <430B6A33.1090004 at erols.com>, Chuck Harris writes:
> 
> 
>>No one has yet addressed the actual oscillator that is on board the sound card.
>>What are they using on the Delta 44?  ... the Aureon Sky?  I would have much
>>more confidence if they would at least use a cheap TCXO module.
> 
> 
> Using a tcxo for a soundcard is the technical equivalent of using
> twelve handpolished and individually goldplated railroad tracks for
> loudspeaker cable:  It would look impressive but be pointless.
> 
> The A/D converters used and the heavyhanded analog anti-alias
> filtering means, that any sort term frequency change in the order
> of 1PMM/minute is not measurable or hearable by any current means:
> the phase difference only shows up as one nanosecond after 44 seconds
> of audio.
>