Short connections (<1m): Buffered i2s or SPDIF? - diyAudio
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Old 3rd June 2008, 09:38 AM   #1
NeoY2k is offline NeoY2k  France
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Default Short connections (<1m): Buffered i2s or SPDIF?

Hi!
I'll need to transmit 8 ch of audio to a DAC, I'll be using a DICE to interface everything.

I can put SPDIF receivers inside the DAC box and run coax or optical cables.

Or I can run i2s, with a buffer chip (or symetrical line drivers?) for each signal. I'd like to run these lines in a sub-d.

Which one will lead to less jitter? What buffer to use for the i2s clock, a clock buffer? But won't there be too much time differences between data and clock? Do you know low jitter chips?

Thank you,
Nicolas
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Old 3rd June 2008, 04:03 PM   #2
kevinkr is offline kevinkr  United States
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I'd use something like National's LVDS differential line driver family to send I2S, and you would use the same device across the board for data and all clocks. You need to choose a device with guaranteed device to device skew specifications. (A few nS would probably be ok)

Not really sure about your choice of connector. Something designed for a controlled impedance environment and high speeds would seem like a better choice. What that would be I have no idea. (yet..)
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Old 3rd June 2008, 04:28 PM   #3
phofman is offline phofman  Czech Republic
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How about CAT5 cable and ethernet connectors, or the shielded version of both?
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Old 3rd June 2008, 04:49 PM   #4
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by phofman
How about CAT5 cable and ethernet connectors, or the shielded version of both?
Seems like a reasonable choice to me, cross-talk between the pairs could be a concern, but LVDS signaling should take care of that issue.
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Old 3rd June 2008, 09:48 PM   #5
NeoY2k is offline NeoY2k  France
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Thank you for your answers

Ethernet won't do the trick running balanced: I need to transmit 8 ch, so 4 i2s DATA + Frame clock + Bit clock.

Cables will be short, should not exceed 50cm.

I could use Ethernet unbalanced (there's only shielding), or use balanced connection on a hd sub-d 15...

I wish I would use some impedance specified cable/plugs, but I need to transmit 6 lines, and here lays the problem...
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Old 3rd June 2008, 11:31 PM   #6
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by NeoY2k
Thank you for your answers

Ethernet won't do the trick running balanced: I need to transmit 8 ch, so 4 i2s DATA + Frame clock + Bit clock.

Cables will be short, should not exceed 50cm.

I could use Ethernet unbalanced (there's only shielding), or use balanced connection on a hd sub-d 15...

I wish I would use some impedance specified cable/plugs, but I need to transmit 6 lines, and here lays the problem...
What's to prevent you from using several ethernet connectors? Balanced LVDS is really preferable to unbalanced, and standard I2S is not designed to be shipped long distances. (I'd say anything over about 5 cm without buffering.)
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Old 4th June 2008, 11:24 AM   #7
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what about some SCSI twisted pair interconnect ?
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Old 4th June 2008, 07:58 PM   #8
NeoY2k is offline NeoY2k  France
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Thank you all
SCSI twisted pair and balanced LVDS should do the trick.

What about the jitter?

Thank you,
Nicolas
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Old 5th June 2008, 07:40 PM   #9
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I use an RS423 driver and receiver for my I2S link and it works fine. I use cat 5 twisted pairs and 9 pin d type connectors over a metre or so and it works fine.

I believe balanced I2S is lower in jitter than SPDIF because of the difficulties caused in making SPDIF self-clocking, and (more importantly) the extraction of the clock at the receiver end.
I2S has none of that problem.

I suspect LVDS would be a better option, but it might be overkill. I recall professionally using LVDS to transmit DVB transport streams in parallel. So, that's 8 data lines and several clock signals in a bundle of twisted pairs running at about 8-10MHz quite happilly, over 10 metres or so (we didn't need to try any further).
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Old 5th June 2008, 08:29 PM   #10
peufeu is offline peufeu  France
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Clock = LVDS
Everything else = plain flat cable
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