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Understanding Jitter in PC Audio

I have a fundamental doubt on the PC audio as a source. IN a traditional CDT/Dac combination we have a clock signal coming out in the SPDIF signal. Apologies if it sounds too silly but am planning of builing an HDD based transport as an alternative to my classe CDT1 :). was planning on a USB output from a dedicated PC and then use a good USB to SPDIF converter.

My Understanding is that in case of a HDD based transport, the File is converted into an Async format (Lossless) . This is then played via a PC/Mac and when given out as digital out, the clock that is synched to is the machines own clock (Am I right ?)

a) does this impact jitter of the Lossless file in anyway ? also what would the difference between an I2S and an USB interface be in this case as the clock is not really the original clock ?
b) Can the original information without any timing errors be reconstructed from this using an external reclocker like the empirical audio device OR Monarchy ?
c) If the clock is not present will an external DAC just assume the input to be as per its own clock. (If the rip were done by CDROM using the same clock freq as a DAc give any added benefit)
arj
detlof
1,899 posts
 
I hope Steve Nugent of Empirical Audio reads this so he can give you an expert answer.
As far as my own two ears are concerned, I feel I can put your "fundamental doubts" at ease. Even with a modest USB to SPDIF converter like the TRENDS, the sound holds its own with very much more expensive CDT/DAC combinations and using Steve's SPOILER with PACE CAR reclocker you get a practically jitter free signal, the sound of which easily surpasses both the Zanden Combo as well as the DCS stack in my rig in all the important parameters we audiophiles love.
shadorne's avatar
shadorne
7,333 posts
 
USB has no clock - it is an asynchronous protocol. If you use USB then you need to makes sure it handles 24 bits and the audio formats you need - that's all.

Jitter

- if you use USB then it all comes down to the clock in the DAC. (and these are all getting pretty good these days)

- if you use a toslink or SPDIF to feed to a DAC then you will undoubtedly have some jitter as most PC's or Imac devices have jitter and an "interface" tends to create jitter. In this case it boils down to the re-clocking algorithm's in the DAC and it may be important to choose the DAC accordingly. If you have a preferred DAC and it is not well regarded for excellent jitter immunity then a "pace car" would be anoher way to go.

As Detlof says - there is no reason you won;t be able to get excellent sound PROVIDED you get bit transparent data to the DAC (watch out for pitfalls in Digital volume controls, equalizers and just general software bugs...for example some verisons of iTunes are good if you know the proper settings and some versions are actually flawed.)
arj OP
68 posts
 
Thanks Shadorne and Detlof,

I already use a Reimyo DAP777 as my DAC.
So if the lossless file is going to be Clocked by either the DAC or by the Clock of the USB to SPDIF converter, it becomes very important that the clock input to the DAC is excellent. which could either be via the USB to SPDIF converter (now i undersand the impoertance to the I2S connection) OR via any external reclocker.

I guess the former would always be more preferable as the chain would be shorter. (?)

Now I do have a Trends converter. I have not really tried out the external battery option yet but it does tend to reduce the volume of output (net gain is lower ?) and the treble is not as detailed as my transport.

I guess that must be the result of the poor clock in it. I do not see any issues with the soundstage though..both the breadth and the depth are quite there...it is the tonality and the harmonics which seem to suffer..

That may be due to Jitter ?. i will also try out the old Monarchy DIP which has been out of the chain for quite some time !
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