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Date: Thu, 10 Mar 2011 19:18:41 +0000
Message-ID: <AANLkTimN8Qb6rDFd5FMAYqdcmWeC6PPpBZseXDPp7NTv@mail.gmail.com>
From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: LF: Re: VLF Stability and soundcard locking
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Have you tried a proper upmarket high quality USB sound interface?  I have
an Edirol UAX-1 here - although its attached to an old LP recrod deck at the
moment (been transcribing old LPs) .  It'll be worth seeing if that suffers
the same issues.  Bet its just as bad

Andy

On 10 March 2011 18:57, James Moritz <james.moritz@btopenworld.com> wrote:

> Dear Andy, Wolf, Markus, LF Group,
>
> I tried some further experiments with the same USB sound card and an
> additional computer (the one I am writing this mail on). The "real" offset
> in sound card clock rate is fairly stable (within a couple of ppm) at
> +48ppm. I reset data in the Spec Lab calibration table to 48000 samples/sec
> nominal and re-measured the sample rate error with the lap-top PC; this was
> -115ppm. I then transferred the USB sound card and calibration source to
> this desk top PC and left it running during the day, checking the sample
> rate error from time to time. The SR error showed small drifts consistent
> with the thermal drift of the sound card clock crystal, together with much
> larger step changes in sample rate, which occured when there was "activity"
> on the PC like opening files or applications, plugging in a USB stick,
> checking e-mail etc. Once the step had occured, the sample rate would stay
> very close to the new rate until the next step occured. It became clear
> there were discrete step sizes - I observed:
> +48ppm (for a frustrating few minutes...)
> -33.5ppm
> -114.9ppm
> -277.7ppm
> -359ppm
>
> If you subtract the +48ppm actual clock offset, you get offsets of:
> 0ppm
> -81.5ppm
> -162.9ppm
> -325.7ppm
> -407ppm
>
> if you calculate what this is in samples/sec at 48k sample rate, it is
> close to: 0, -4, -8, -16, -20 samples/sec, so it looks like samples
> evaporate in groups of four... interesting, if not directly useful! I will
> be interested to try this with other PCs to see if the result is the same.
>
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
>

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<div>Have you tried a proper upmarket high quality USB sound interface?=A0=
 I have an Edirol UAX-1 here - although its attached to=A0an old LP recrod=
 deck at the moment (been transcribing old LPs) .=A0 It&#39;ll be worth se=
eing if that suffers the same issues.=A0 Bet its just as bad</div>

<div>=A0</div>
<div>Andy<br><br></div>
<div class=3D"gmail_quote">On 10 March 2011 18:57, James Moritz <span dir=
=3D"ltr">&lt;<a href=3D"mailto:james.moritz@btopenworld.com">james.moritz@=
btopenworld.com</a>&gt;</span> wrote:<br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8e=
x; PADDING-LEFT: 1ex" class=3D"gmail_quote">Dear Andy, Wolf, Markus, LF Gr=
oup,<br><br>I tried some further experiments with the same USB sound card=
 and an additional computer (the one I am writing this mail on). The &quot=
;real&quot; offset in sound card clock rate is fairly stable (within a cou=
ple of ppm) at +48ppm. I reset data in the Spec Lab calibration table to=
 48000 samples/sec nominal and re-measured the sample rate error with the=
 lap-top PC; this was -115ppm. I then transferred the USB sound card and=
 calibration source to this desk top PC and left it running during the day=
, checking the sample rate error from time to time. The SR error showed sm=
all drifts consistent with the thermal drift of the sound card clock cryst=
al, together with much larger step changes in sample rate, which occured=
 when there was &quot;activity&quot; on the PC like opening files or appli=
cations, plugging in a USB stick, checking e-mail etc. Once the step had=
 occured, the sample rate would stay very close to the new rate until the=
 next step occured. It became clear there were discrete step sizes - I obs=
erved:<br>
+48ppm (for a frustrating few minutes...)<br>-33.5ppm<br>-114.9ppm<br>-277=
.7ppm<br>-359ppm<br><br>If you subtract the +48ppm actual clock offset, yo=
u get offsets of:<br>0ppm<br>-81.5ppm<br>-162.9ppm<br>-325.7ppm<br>-407ppm=
<br>
<br>if you calculate what this is in samples/sec at 48k sample rate, it is=
 close to: 0, -4, -8, -16, -20 samples/sec, so it looks like samples evapo=
rate in groups of four... interesting, if not directly useful! I will be=
 interested to try this with other PCs to see if the result is the same.=
=20
<div>
<div></div>
<div class=3D"h5"><br><br>Cheers, Jim Moritz<br>73 de M0BMU <br><br></div>=
</div></blockquote></div><br>

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