SPDIF Input Upgrade

[Ray P]

I'm currently considering my options for integrating streamed music into my main audio system (currently use a logitech squeezebox on the home cinema system) so a sort of hypothetical question to check something out.

Assume I have an upsampling CD player, equipped with 24bit 192KHz Burr Brown DAC chips - playback of CDs can be upsampled to 96KHz or 192KHz. The CD player also has an SPDIF digital input to allow the onboard DAC to be used with external sources, such as a squeezebox, but only supports upto 16bit 48KHz data. I assume it is possible to feed the DAC data at upto 24bit 192KHz but is there anyway (or preferably somebody capable) of upgrading the SPDIF input to achieve this, whilst retaining the upsampling option for CD playback?

There seem to be a number of CD players configured as I describe and it would be good to be able to feed their onboard DACs with high resolution download files as a cost effective solution to a mixed media environment.

Ray

[Nick]

It would depend on how it was all connected internally. If the CD source produces 16/44 i2s that was then upsampled and then to the DAC. It would in theory be possible to take the spdif signal directly into the dac bipassing the upsampling and so assuming the spdif input could handle 192/24 it would work. It may be that the spdif goes into the upsampler which is why its restricted to CD data rate.

[Ray P]

Thanks Nick, I believe the SPDIF is routed to the upsampler so that would need to be bypassed. I know there are 24bit 192KHz SPDIF inputs out there in the marketplace but its the execution I'm not sure of.

I assume that the SPDIF input would need a suitable 'module' to convert the hi-res data to I2S that would be routed to the DAC chip inputs but don't know enough about the technology to do anything practical. I guess there may also be a question about source switching at the DAC if you bypass part of the internal circuitry. I believe the DAC chip will automatically switch according to the sampling rate being received.

I think I would need to find someone who can offer an upgrade service.

Ray

[Nick]

This would do the first part

http://www.twistedpearaudio.com/digital/wm8804.aspx

This would do the second

http://www.twistedpearaudio.com/control/otto.aspx

The problem would probably interrupting the i2s lines, assuming the DAC was using i2s and not something else.

It would be a hack, but theoretically entirely doable.

[Ray P]

Thanks Nick, I'll peruse a bit later.

Ray

[andrew Ivimey]

At a more mundane level, my understanding is that spdif is not the best signal compared to what comes out of the coaxial digital socket of a DAC.

Am I correct in believing this?

[ed]

digital output of a dac?

[andrew Ivimey]

ha ha ha ha ha oops - christ I'm tired!

... co-axial digital output from a CD player.

[Nick]

ha ha ha ha ha oops - christ I'm tired!

... co-axial digital output from a CD player.

I think that normally is S/PDIF

http://en.wikipedia.org/wiki/S/PDIF

[andrew Ivimey]

okay and this is different from SPDIF is it? I really don't know.

[Nick]

I think it IS SPDIF.

[andrew Ivimey]

Which means it is not different, so ... am I right in thinking that SPDIF is inferior to coax digital ???

[Mike H]

Does he mean S/PDIF is coax digital?

Coax digital is S/PDIF, etc...

Can be both electrical or optical according to that wiki page

 

[Nick]

No, I am trying to say that SPDIF IS Coax Digital. Just to confuse things, the optical transmission via fibre and toslink connectors is also SPDIF. SPDIF describes the digital format (the sequence of high and low and what it means) and the physical medium, 75R coax or Optical.

[andrew Ivimey]

Ah, thanks for that.

I can hang on to that. Now, is an spdif signal degraded by being optical compared to the co-ax signal?