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

[Ralf Mardorf]

Ralf Mardorf wrote:
> Olivier Guilyardi wrote:
>> On 05/28/2010 07:36 PM, Ralf Mardorf wrote:
>>  
>>> Folderol wrote:
>>>    
>>>> On Fri, 28 May 2010 19:20:54 +0200
>>>> Ralf Mardorf <ralf.mardorf at alice-dsl.net> wrote:
>>>>
>>>>  
>>>>      
>>>>> Veronica Merryfield wrote:
>>>>>           
>>>>>> 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.
>>>     
>>
>> I mentioned the clock problem first ;-) However, I thought it the 
>> other way
>> around: I said that clocks being asynchronous that would generate 
>> artefacts, but
>> Veronica seems to say that these are hidden when using a single clock.
>>
>> That's pretty much the same thing to me :p
>>
>> -- 
>>   Olivier
>>   
>
> Did you also say for what card? A or X? If so, is Oliver the winner?
>
> Btw.:
>
> Ralf Mardorf wrote:
>> Gabriel Beddingfield wrote:
>>> On Fri, May 28, 2010 at 12:39 PM, Gabriel M. Beddingfield
>>> <gabrbedd at gmail.com> wrote:
>>>  
>>>> The 100 Hz (being 2x 50Hz, the power freq. in Italy)
>>>> suggests that it is probably related to some manner of
>>>> power supply.  However, I have no theory why we're
>>>> getting 2x 50Hz (and I think I need one :-)).
>>>>     
>>>
>>> Doh!  When the AC wave is rectified, it results in a signal that is 2x
>>> the freq. because the negative part gets inverted.  That's why we see
>>> 100 Hz instead of 50 Hz.
>>>
>>> -gabriel
>>>   
>>
>> On card A or X?
>> Why AM and not additive signals? 
>
> Is the jitter caused because of residual ripple?
>
> Summarized:
>
> Residual ripple for the DC could cause clock jitter and this for card A.

And more:

Clock jitter would cause AM (<-- not my knowledge, somebody else wrote 
it) instead of analog hum, that would cause an additive signal.

@ Oliver: Didn't you talk about syncing both cards? That's irrelevant.