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Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?

To: [email protected]
Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?
From: Andy Talbot <[email protected]>
Date: Wed, 25 Apr 2012 14:46:00 +0100
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Has anyone tried using an external USB soundcard with a separate
locked clock?   Most work from a 12MHz crystal which can be replaces
with a GPS locked source without too much effort. But I can't help
wondering if there will be subsequent USB synchronisation glitches
upsetting the input sampling.

Although I have used many different USB soundcards and chips, somehow
never managed to get round to actually trying this myself - so hoping
someone else has....

Another thing I was wondering, the soundcard chip wants 12MHz  (well,
the PCM2900 does anyway) and a USB hub chip can have a 6MHz crystal
option. So... is there any value in synchronising this 6MHz by
dividing down from the Soundcard clock.  Could there still be USB
slippage?

My old simple 8 bit PIC serial A/D still offers an absolutely phase
coherent sampling as it chucked the data up a non-coherent serial port
so none of the potential slippage issues USB seems to give.
Why does the nice ubiquitous USB port seem to have been a backwards
step in this respect.

Andy
www.g4jnt.com


> That can happen when multiple phase glitches occur on the PC, sound output.
> Try to use a different sample rate, maybe 44100 instead of 48000.
> Try to run SL exclusively, i.e. no other programs and internet usage
> (everthing that may take a high CPU load) and see if it makes a difference.
> The signal of DJ8WX is clear. That reduces the possible errors...
>
> 73, Stefan/DK7FC


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