Most of my previous suggestions were intended for Frantz and his own requirements (while Bruce could answer us -both-).
Thanks for the long reply. I was really replying to both you and Frantz.
Bruce said that he preferred SPDIF to USB or Firewire. I am not sure whether his preference was specific to output from a computer or if it referred to both input and output.
> I was wondering if it could help to improve the accuracy in case I decide to use an external
> Hi-End PRO DAC. In that case, I would send the digital data from the Delta to an external DAC.
For an ADC device, the same clock can drive the ADC process and generate the clock portion of
the SPDIF stream that is sent to a computer. In the computer, the digital data stream will normally be stored without a digital-to-analog operation for which low jitter might matter. The simplest implementation is fine.
For SPDIF output from a computer to a DAC box, the simple implementation is not so fine. You don't really want the clock embedded in the SPDIF stream to drive the d-to-a operation. So we might need a fancier DAC implementation to reduce jitter in the clock recovered from the SPDIF stream. Fancy PLLs, async resampling and big buffers are possibilities.
We might also consider sending a clock signal from the DAC box back to the computer to be used to drive the SPDIF output. There are some disadvantages:
- Since not every DAC can supply a suitable clock output, we are narrowing our choice of DACs.
- Since not every soundcard (or onboard sound) can accept a clock input, we are narrowing our choice of soundcards.
- An increasing number of audiophiles choose a laptop or a computer like a Mac Mini that has no PCI or PCIe slots. Have you seen a laptop that accepts a clock input for use in audio output?
- You might want to be able to output a mix of 44.1, 48, 88, 96, etc. content and have the DAC sense the clock rate of the input stream. When the DAC is generating the clock for the SPDIF, you may have to manually set the clock rate on the DAC every time you want to output something at a sample rate different from that in use.
Don't just assume that using SPDIF with a word clock cable from the DAC to the computer is your only option or the best option.
Most people who design DACs functionality will tell you that the lowest jitter solution is one where the clock is generated very close to the actual DAC chip and does not have to be adjusted to an incoming data stream and clock. PCI, USB and Firewire based interfaces can all achieve very low jitter and provide a good control interface for automatically adjusted to output sample rate and setup. All sorts of new async mode USB DACs are coming out now at various price points.
A comment on the RME ADI-2 and the Babyface. RME packages similar AD/DA functionality in a number of products with PCI, USB, Firewire and just SDPIF/AES/EBU interfaces. It is up to the buyer to select the product that fits his needs. RME gear is more expensive than M-Audio or Echo or some other pro-audio brands. Driver quality is one reason to buy RME.
I used the Babyface as an example of a RME product that provided a complete computer interface and DAC function. The ADI-2 is just an outboard AD/DA. The Babyface or a used RME Multiface are possibilities I'd consider.
Similarly, the TC Electronic BMC-2 appears to have similar DA capabilities to the Firewire based Konneck 6. Both products are on my short list for a DAC change.
MADI and jitter reduction: You provided a link to RME's description of their jitter reduction technology. The example of treating a jittery input clock from a MADI stream is scary. The jitter on the MADI stream is quite high. The level of jitter after RME's jitter reduction is lower but not low by the standards of async mode USB DACs like wavelength's and Ayre's. Is the difference in jitter levels audible?
Why value would MADI give you? Do you need long runs? Do you need many channels?
A comment on number of channels in Pro Gear: M-Audio, Echo, ESI, E-MU and others have solutions for 2 or 4 channels that are cost effective. The Lynx L22 card is a two channel version of the Lynx Two card.
Bill
. Unfortunately most of professional DACs (not all) have the ability of being AD/DA and, most of them have been designed to "deal" with many channels. I agree with you that it is a pity (i.e. waste-of-money) to get a 14 or even only 6 DAC analog outputs for our needs: just 2 analog channels... 
