Which high end, low jitter, SPDIF optical card?

[Andy8421]

I am building a high end HTPC. I have a decent AV processor (Krell Showcase driving Krell amps), so want to use its DACs rather than a sound card's audio outputs. Plan is to use optical SPDIF output from the PC to drive the Krell.

I want to ensure the SPDIF is as low jitter as possible and am prepared to pay up for a decent soundcard, understanding that the analogue components of the card will be unused.

I have seen reference to RME and Lynx as good quality cards - is there a good manufacturer who specialises in low jitter SPDIF that I should use?

Thanks in advance...

Edit: There are other threads on high end cards on the forum, but focusing on analogue outputs. I want the best SPDIF optical card - mod please move if this post is too similar to other threads.

[badbob]

I want to ensure the SPDIF is as low jitter as possible

Optical has something like 10x higher jitter than coaxial...so don't use optical.
I'm using a M-Audio Revolution 5.1, it has coaxial digital output (RCA) 44.1khz works (rather than displaying as 48khz on my Lexicon) , as does dolby digital & DTS for DVD's. DTS WAV files are a problem, not sure why..

[Andy8421]

Badbob,

Thanks for the reply. I will check out M Audio Revolution.

I too have heard that optical suffers from worse jitter, but I have never seen any real analysis to prove it. The attraction to me of using optical to keep any PC generated RFI away from the Krell, and to avoid ground loop problems.

Can you point me to any analysis on optical vs Coax?

[drummerjohn]

Originally Posted by badbob

Optical has something like 10x higher jitter than coaxial...so don't use optical.
I'm using a M-Audio Revolution 5.1, it has coaxial digital output (RCA) 44.1khz works (rather than displaying as 48khz on my Lexicon) , as does dolby digital & DTS for DVD's. DTS WAV files are a problem, not sure why..

Use ASIO for the the DTS WAV files. ASIO4ALL

[badbob]

Not sure what settings to use for the card in that util.
woot working in Winamp! Needed to install Asio plugin then change to asio4all. Last time it didn't work. DTS works in winamp :-) not working in WMP, WMPC or VLC. Got it working in foobar, again asio plugin required. I have left and right channels in foobar, do I just add one or both? If I add both then two asio4all options are available in output devices. It's stereo either way, if I just have one selected.

[drummerjohn]

I have only ever tried winamp and I when I installed ASIO4ALL I don't remember making any changes. I forgot to mention the out_asio.dll file that you can put in winamp plugin directory as well. Then configure winamp to work with the plugin. I can send it to you if you want - PM me.

[dogbert]

having a low jitter spdif port is completely and utterly pointless if the signal's receiver is a DAC which has been made in the last ten years. paying more for an SPDIF port than the minimum price is effectively paying idiot tax.

[Andy8421]

Dogbert,

The processor has to recover the clock from the SPDIF link, typically using a PLL or similar approach. The recovered clock is used to sample the SPDIF bitstream (to recover the data) and to set the clock rate for the processor. The jitter has to be extreme to cause input data errors, but even in a decent set-up which buffers and reclocks the DACS (the Krell I use buffers then oversamples up to 192KHz and 24 bits) the average clock rate of the processor has to equal the average clock rate of the input data. If the average rates aren't equal then the the DAC buffers will overflow or run out of data depending on whether the source is running faster or slower than the processor.

The effect of reclocking is to filter out the higher frequency jitter, but depending on the size of the buffer, and how closely the processsor tracks the SPDIF clock, lower frequency jitter still gets through.

Whether this is audible, or whether I am worrying about nothing is a different issue. Given the £££ I have frittered away on my system, I am happy to pay a few more £'s Idiot tax to have one less component in the chain to worry about.

[MI55ION]

Originally Posted by dogbert

having a low jitter spdif port is completely and utterly pointless if the signal's receiver is a DAC which has been made in the last ten years.

I don't understand that statement, could you please explain why it is pointless?