Wolfson's Elastic Buffer SPDIF receiver ?

[percy]

Found this AES paper from Wolfson's website - http://www.wolfsonmicro.com/uploads/...Oct%202006.pdf

But I couldn't find any of their spdif receiver products that have this architecture ? Did wolfson ever start production of this kind of receiver ?

Does anyone else make an spdif receiver that works on the same principal ?

[Iain McNeill]

Call me a naysayer but I think all these schemes are flawed. This one appears to have a small buffer and then they continually speed up or slow down the data out clock to stop the buffer over/under-flowing. Not particularly original.

By keeping the output clock fixed for short periods of time and occasionally making incremental changes, the instantaneous jitter is reduced by an order of magnitude - Bravo! But there are still going to be small temporal distortions over the time frame of a song/album/movie.

I'm still not convinced that the ASRC method which is currently in vogue is any better. Here, the incoming data, which we assume has been recorded with a jitter free clock is arriving at a non-constant data rate. The idea of upsampling to a massively oversampled clock and then phase interpolating the samples to the output clock points in time is equally disruptive.

Ideally, you'd just output those precisely recorded samples at a constant rate.

I still think the best way is to have a HUGE buffer, I'm talking like a GB or so and just play everything back at 0.1% slow to a rock solid clock. OK by the end of the movie you'd have accumulated a couple hundred meg of buffered data, the movie would go on for a few minutes after the DVD stopped spinning. No biggie, small price for perfect playback.

[Wodgy]

For what it's worth, the eye diagrams in the AES paper you link to are reproduced in this white paper analyzing the performance of the WM8804/5:
http://www.wolfsonmicro.com/uploads/...May%202007.pdf
So it's probable that the WM8804/5 do include "elastic buffers" even though this isn't specifically mentioned in their datasheet.

[percy]

Wodgy, yes I saw that paper too, but I was hoping to find a more definite confirmation. Even the functional block diagram of the chips in both their datasheets as well as this paper don't reveal anything specific in that matter.

[percy]

The only other unofficial reference I found to this is - http://www.electronicsweekly.com/Art...chitecture.htm

It does say that "The firm’s WM8804 and WM8805 chips include the new scheme"

[percy]

this becomes interesting - contacted Wolfson directly, I was told their current spdif receivers (wm8804/5) do NOT have the elastic buffer technology. I wonder how in the world then are they able to acheive that feat ?? As shown in a chart (pg 5, fig 2) jitter rejection in the wm8805 starts as early as 100hz and increases dramatically by 1-2Khz.

[tritosine]

haha , good to know, thanks percy , maybe they should discontinue their dac and put that receiver into production