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s/pdif 2 mono sources to one stereo input?

Discussion in 'Recording' started by jonnyadlib, Apr 22, 2007.

  1. jonnyadlib

    jonnyadlib Guest

    Hey guys I just joined the forums. Right now I'm doing Cubase based recording using a firepod. Recently we bought two M-Audio Tampa preamps for the studio (which btw sound amazing) and they each have a mono s/pdif digital output. The firepod has a single stereo s/pdif input (and output but that doesn't matter) and I was wondering what I need to find to hook both preamps up or even if I could. (this isn't the only input but if I could get the tampas running through the spdif I'd have 2 extra channels for scratch guitars and/or more drum sounds, etc.) I've been searching for y-cables but I'm figuring that since it is digital I'll have to do some sort of converting, like flipping one mono channel to the opposing channel of the stereo or whatever. Also will I be losing quality or gaining quality by going through the spdif? Any help would be great. Later.
  2. sheet

    sheet Well-Known Member

    No you cannot do what you are asking. You cannot combine two mono S/DIF outputs with a Y cable to connect them to a stereo S/DIF input.
  3. Boswell

    Boswell Moderator Distinguished Member

    Yes, I scratched my head over the decisions that M-Audio made when designing the Tampa. It looks a nice unit, but to have a 24-bit S/PDIF and AES/EBU output with the same signal in both L and R channels (i.e. mono) and no facility for daisy-chaining a second Tampa to use the redundant channel is really strange.

    I know of NO digital mixer or interface that has two S/PDIF inputs that can be mixed together (as opposed to being switched between), so to use more than one Tampa, you are forced into using the analog outputs. At least that will work, even if it means a loss of quality.
  4. sheet

    sheet Well-Known Member

    Well, AES and S/PDIF are the only two options really. Every other digital protocol is multichannel. So it was either use of two or one of eight.

    It is a drag. Maybe someone needs to make a digitail mixer/firewire computer interface with more S/PDIF. But, how would you sync it all? Not all digital outputing gear has sync options.
  5. Boswell

    Boswell Moderator Distinguished Member

    Some years ago I had to design a modular instrumentation unit that needed optical connection for electrical isolation reasons, and I chose ADAT as the data transmission protocol. Each module had an ADAT in and ADAT out. If an in was present, a unit would sync to the incoming stream and append its data as the next unused channel in the the ADAT channel list, and forward the updated stream to the ADAT out. As the sampling rate was only 25KHz, I could sub-divide a 50KHz 256-bit ADAT frame into 16 channels. In that way, up to 16 modules could automatically link together, synchronised.

    It would seem to me quite straightforward to have pro audio gear such as single and dual-channel pre-amps having something like an ADAT in and out, and auto-syncing to an input stream if present. Nowadays with sampling rates up to 192KHz, a dual-channel preamp could take up all the ADAT bandwidth, so maybe a higher rate protocol would be better. If optical connection were not needed, then a scheme based on the new external cable standard for PCI Express would give around 2Gb/s raw data rate per line of PCI-e. This is over 160 times the capacity of an ADAT lightpipe. This standard, and corresponding external connectors, will soon be appearing on computer motherboards, thus presenting a ready interface into a DAW.

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