John Bowen Synth Design

John Bowen wrote:Hi marzz,
I've been told that there's some lack of clarity to the S/PDIF specification when it comes to defining the higher sample rate of 96kHz. The engineer will look into it more this week.

john

I'm interested to see how this plays out. I want to get a new audio interface, and the thought of running the Solaris digitally into a Metric Halo ULN-8 has got me pretty excited. Can anyone see a reason why I couldn't connect the rca spdif out of the Solaris into the ULN-8's AES/EBU port with the right adapter cable?

The Solaris S/PDIF is optical, not RCA.

-john b.

Thanks for pointing that out, John. For some reason I thought Solaris had both rca and optical outputs. I've seen converter boxes that solve this interfacing problem, but it's a messy solution. Oh well...

John Bowen wrote:Hi marzz,
I've been told that there's some lack of clarity to the S/PDIF specification when it comes to defining the higher sample rate of 96kHz. The engineer will look into it more this week.

john

JB- thanks for looking into this. I would love to be able to run everything at 96K, and the idea of taking the direct digital out of the Solaris and using the (possibly higher quality) Apogee D/A convertors is appealing.

Oh, and don't forget PolyAT response in the MIDI spec!! thx!

In what we could find (both myself and the engineers), S/PDIF is identified as the 'consumer' version of AES/EBU standard. While the data is (mostly) compatible, the consumer spec is only there for 48, 44.1, and 32 kHz. It's also the case, however, that the spec says the format has "no defined data rate". Note this quote from a Wikipedia post:

"S/PDIF is used to transmit digital signals of a number of formats, the most common being the 48 kHz sample rate format (used in DAT) and the 44.1 kHz format, used in CD audio. In order to support both systems, as well as others that might be needed, the format has no defined data rate. Instead, the data is sent using biphase mark code, which has either one or two transitions for every bit, allowing the original word clock to be extracted from the signal itself."

It is this lack of definition that has the engineer uncertain as to what is possible with the built-in S/PDIF processor of the SHARC chip.

As to bit depth, I am told the intention is to use 24-bits. Again, from Wiki:

"S/PDIF is meant to be used for transmitting 20-bit audio data streams plus other related information. To transmit sources with less than 20 bits of sample accuracy, the superfluous bits will be set to zero. S/PDIF can also transport 24-bit samples by way of four extra bits; however, not all equipment supports this, and these extra bits might be ignored."

Further testing next week should provide confirmation on this.
-john b.

It is my understanding that SPDIF is also not properly defined for any sample rate above 48 KHz. I have asked Eventide about this because I wanted to use my H-8000FW with SPDIF but they said: "it might work but it's definitely not recommended".

ADAT is also not directly defined for anything above 48 KHz. You can get 96 if you sacrifice bandwidth, for instance one could have say 8 channels at 48 KHz or 4 channels at 96 KHz, with a technique which is called multiplexing.

In my opinion the best way to go 96 KHz is first AES/EBU and then Firewire. It's my understanding that all internal processing in the Solaris is done at 96 KHz so it would be cool to have that signal directly out of the instrument with no conversion whatsoever.

John, did you consider AES/EBU or was that, for some reason, not an option?

Regards,
Yannis

ThreeFingersOfLove wrote:It's my understanding that all internal processing in the Solaris is done at 96 KHz so it would be cool to have that signal directly out of the instrument with no conversion whatsoever.

Basically my sentiments exactly.

The fact of the matter is that putting AES instead of S/PDIF would have added even more to the cost. And it's not just the physical connectors - you have to add an additional transformer as well. (Not to mention installing those XLR connectors is not so fun!)

Now, given the ongoing pricing of the Solaris (which is sure to increase once it goes through the dealer network as well), I can hear people saying that the Solaris is already hitting the 'deluxe' price point, so what's another couple of hundred $$ for AES? Well, maybe you'd be right - but this is something we'll have to address in a future 'super deluxe' version.

By the way, the guys here (in Germany) ARE looking into a way to get 96khz to work with the S/PDIF connector. It seems that there's a possible path by having the Solaris determine the rate from the S/PDIF Input signal, and adjust the Output accordingly.
-john b.

Perhaps the AES connectors can be sold as a separate upgrade option? I/O upgrades are quite common in high-end gear.

As far as a "super deluxe" version, mine would have a polyAT keyboard!

I am fully willing to pay more for AES/EBU on the Solaris. I'd love to see it happen. (That's it for my hardware wishlist.)

lotus-eater wrote:I am fully willing to pay more for AES/EBU on the Solaris. I'd love to see it happen. (That's it for my hardware wishlist.)

Me too. Just make it happen and everyone will be happy!

Still in Germany today - our preliminary tests yesterday Using a Scope system running at 96 kHz as Master, we sent the S/PDIF Output from the Scope board to the Solaris S/PDIF input, and then back from the Solaris S/PDIF Output to a different board S/PDIF Input (An older Pulsar card, but still running Scope software, of course) and we successfully got Solaris to run the signal at 96 kHz!

Full investigation will continue....
-john b.

Back home a week now...only to return for Frankfurt Messe the end of this month!

It does seem that you can get the Solaris to output at 96kHz in the manner I described - it is 'slaved' to the S/PDIF input rate, and will then run the output at the same rate.

JB

My little firewire interface will do 96KHz/24-bit either in or out on SPDIF. So Solaris running at 96KHz/24-bit is great with me.