[LAD] A little quiz about audio measurements...

[Ralf Mardorf]

Folderol wrote:
> On Fri, 28 May 2010 19:20:54 +0200
> Ralf Mardorf <ralf.mardorf at alice-dsl.net> wrote:
>
>   
>> Veronica Merryfield wrote:
>>     
>>> On 05/28/2010 02:31 PM, fons at kokkinizita.net wrote:
>>>   
>>>       
>>>> Hello all,
>>>>
>>>> This week I had to perform measurements on a audio
>>>> interface, and this resulted in some quite interesting
>>>> results. Before revealing what happened, I'll let you
>>>> have a look at some of the data and come up with your
>>>> own conclusions, see
>>>>
>>>> <http://www.kokkinizita.net/linuxaudio/quiz.html>
>>>>
>>>> (Free beer at the next LAC for the best analysis)
>>>>
>>>> Ciao,
>>>>
>>>>     
>>>>         
>>> You can't trust a loop back test. 
>>>
>>> Any instability or dither on the reference clock of card A (fifo clocking say) is not going to show in a loop back test. 
>>>
>>> Vrnc
>>>       
>> Is Veronica Merryfield the winner?
>>     
>
> I'm highly suspicious of the USB link, but can't quite put my finger
> on why.
>   

Card A is the USB card. For USB there could be several issues, but I 
don't have knowledge about buffering etc., but I guess it's card A and 
that there's  a "instability" = jitter. I don't know what dither for CLK 
is. I guess the winner is Veronica Merryfield.