[Tril]

Andrew's S/PDIF Stuff

At the bottom of the page, it mentions someone using a 2.4Ghz video sender from Radio Shack to transmit S/PDIF data in his house.

It says that it works but I'm wondering how good/bad the clock is after that transmission. I'm guessing not very good for high quality audio. It probably does not reclock the signal (since it also works with video) although I don't know for certain if it doesn't.

It's the first time I heard about this.

Anyone tried it before?
What's your experience with this?

 

[ericj]

Well, those video senders are pretty low quality.

On the other hand, they use as much bandwidth as three 802.11g channels, so you'd think they could transmit something as piddly and slow as digital audio.

It's going to be lossy. Frames are going to get lost. Especially if somebody turns on the microwave.

It'll generally work. Probably better than using an FM transmitter. But not better than a wire.

 

[Tril]

wireless routers and wireless network cards can transmit digital data successfully. There's probably some error checking that improves thing a little and recovers data if there are errors.

What I'll say may be stupid but :

If it's possble with computer data, it should be possible with S/PDIF. Why is it not the case (at least, not perfectly)? Is the transmission of the clock signal the main difference?

Is this subject something where DIY can be used? I'm thinking that it may not be well suited to DIY engineering because the issue of transmitting radio waves on a device non approved by the FCC may be illegal.

I don't have a use for this currently but if technology evolves, it may come in handy someday (if it improves enough to equal a good S/PDIf cable).

 

[amb]

Computer wireless LANs ride on top of the TCP/IP software stack which provides data integrity checking and correction, including retransmission of packets, etc. if necessary. I don't know what protocol the wireless S/PDIF rides on, but if it's TCP/IP or something as good, then there is no reason why it shouldn't work well. Data latency may be a problem, so a good amount of buffering will be necessary for smooth, glitch-free audio.

 

[Garbz]

Actually I disagree jitter would be a massive problem. The TCP/IP spec provides for data arriving in the correct order and has no mention of data arriving given a certain time. It's easy to test this by simply starting a file transfer and unplugging a cable. The datatransfer holds untill timeout and resumes when you plug this back in. Sending S/PDIF in the same fashion will result in lost samples and lost signal lock. Whatever he's done to get it working I doubt normal networking protocols are it.

I'm not saying it won't work. Just not very well. I dare say at a minimum asynchronous reclocking would be required on the DAC side, as nasty as it is.

 

[Pat Kelly]

Marmitek has a nice solution to wirelessly send SPDIF. The Audio Anywhere 685:
http://www.marmitek.com/en/product-details/listen/wireless-music/digital-audio-transmitters/audio-anywhere-685.php
You can use both coaxial and TOSLINK together.
So for example Coax at the transmitter and TOSLINK at the receiver.