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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: I'm not smart... posted by Presto on April 18, 2007 at 10:14:20:
The *less* circuitry and wires that you have, the better the end result. Complicated design just adds more opportunity to introduce jitter.What I'm looking for (which I haven't found yet) is an external multichannel DAC that has the following features:
- MUST use a *current generation*, flagship DAC chip (ie. BB PCM1794, AKM4396 or CS4398) capable of exceeding 120dB
- dedicated and switchable 44.1 and 48 clocks (NO PLL)
- located as close to the DAC chips as possible (to minimise EMI sensitivity)
- no upsampling
- The digital signal comes in ASYNCHRONOUSLY (ie. "unclocked") and gets clocked by the DAC itself - this can be a simple memory buffer but care must be taken that the wait states are consistent and predictable - static RAM would probably be betterUnfortunately, that rules out just about every DAC unit out there on the market today. Can't use Firewire - too much jitter. The only interfaces I can think of that supports asynchronous (other than proprietary ones) are USB and Ethernet. USB async mode is buggy in Windows XP, and Ethernet introduces too much latency.
So far, the only device that come anywhere close to the ideal (but still not perfect) is the E-MU 1820M, which uses a proprietary shielded (STP) cable to communicate asynchronously between the 1010 PCI card and the external AudioDock. Unfortunately the external unit also draws power from the PC via the STP (but I suspect E-MU wanted to minimise ground loop issues - as far as I can tell from looking at the board layout these guys are pretty smart and know what they are doing)
The only USB async device I've found is the Edirol SD-90, which uses a proprietary asynchronous USB driver written by Edirol (unfortunately, the unit only supports 44.1 and 48kHz sampling rates, and requires a "reboot" to change sampling rates). ThomasPf says the Audigy NX also supports async, but not sure whether Creative has written a proprietary async driver. Neither of those contain flagship DAC chips.
I would also include the Slim Devices Transporter (Ethernet connection, proprietary protocol) but only 2ch.
I'm thinking it should be possible to produce something similar to the 1820M, but using USB2 async and a proprietary driver (or the standard driver in Vista), and preferably using BB PCM 1794 in differential mode (or AKM4396). And externally powered. Such a unit should not cost much more than an 1820M, in fact potentially should be cheaper than a 1820M (if it is a DAC only and doesn't include ADC).
If you know of something like this, let me know. I think the problem is very few people (apart from myself) would buy such a unit. The market is obviously selling overpriced and overengineered SPDIF DACs to well heeled audiophiles. :-)
If I have spare time on my hands, I would build it myself. Unfortunately, I don't, so I keep hoping someone else would do it for me.
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Follow Ups
- Remember - KISS is best - Christine Tham 14:52:29 04/18/07 (3)
- Re: Remember - KISS is best - endust4237 14:06:48 05/01/07 (0)
- just a bit more information on clocks to help you understand - Christine Tham 18:13:39 04/18/07 (1)
- Thanks Christine. You're a walking wiki. That's a keeper. :o) nt - Presto 13:46:55 04/19/07 (0)
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