1 Topic by mike G (edited by mike G 2022-12-25 11:36:00)

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Topic: Why is s/pdif not so popular?

Just curious why more external FX units and even interfaces don't take advantage of more s/pdif I/O on the back? I don't know if optical ADAT is considered the new alternative, but I've heard from a few people that it can suffer from jitter. I won't speculate on that because I don't know. But as far as s/pdif goes, it seems to work great for me. It not only transfer midi data, but my reverbs, delay and chorus's comes into the computer all digital with no conversion. And s/pdif does not seem to suffer from noise as it's just 1s and 0s going down the line.

It just seems like a no brainier to me, that s/pdif would be cheap to implement. If you're lucky most interfaces will give you one, some don't give you any. I know on my T.C M1 FX unit, you can assign 2 independent stereo channels with the correct FX routing with one s/pdif in-out. The Right and Left each go to their own engine in the M1 and then are summed into stereo as two separate FXs. If there were 2 or 4 s/pdif connectors on modern interfaces, you could have more external FX units coming in all digital.

I know software plugins are the popular thing today, but there is still a huge advantage to using external units with regard to taking a load off the CPU. Especially with dense reverbs.

  • cyrano
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Re: Why is s/pdif not so popular?

It's not so cheap to implement, since you need AD/DA added.

It's not expensive either, but as not many manufacturers add it, it isn't popular. And as it isn't popular, nobody feels like they need it.

Me, I've been an ADAT nut for years now. I can shuffle sets of eight channels between three computers and some peripheral gear.

Optical means electric isolation, so no ground problems between setups.

Long optical cables also don't pick up any environmental noise. And they're dirt cheap these days, compared to copper.

And with the two ADAT to UTP boxes from appsys.ch I can run 32 channels over an ethernet cable up to 80 meters or so, so the heavy multi can stay in it's box.

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3 Reply by ramses (edited by ramses 2022-12-25 13:15:01)

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Re: Why is s/pdif not so popular?

mike G wrote:

Just curious why more external FX units and even interfaces don't take advantage of more SPDIF I/O on the back? I don't know if optical ADAT is considered the new alternative, but I've heard from a few people that it can suffer from jitter. I won't speculate on that because I don't know.[…]

With RME you have Steadyclock and by this you do not need to worry about clock jitter from digital inputs.
It successfully eliminates clock jitter even from heavily jittered signals and refreshes the clock signal.
SteadyClock [FS] is being implemented in all RME recording interfaces, preamps, and AD/DA converters.

https://www.rme-audio.de/steadyclock-fs.html
https://www.rme-audio.de/de_steadyclock-fs.html

In addition to SteadyClock FS, ADI-2 DAC/Pro have a design so that their internal FS clock is being used for the final D/A conversion. From what I read here in the forum, this is a unique feature of these reference converters.

For devices of other vendors, this might be different.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

4 Reply by mike G (edited by mike G 2022-12-25 20:27:12)

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Re: Why is s/pdif not so popular?

Good answers guys.
By the way, one correction to what I said above: When I said, "why are there not more on FX units and Interfaces." I meant just interfaces, I don't think you need more then two on an FX units. Anyway.

Regarding ADAT. So it sounds like from all the past rumors, it was really the clocking that was the issue, not the optical. Good to know. The reason I was questioning it was,  I remember my recording engineer friend telling me this. And he always used a BIG Ben from Apogee. But that was like 25 years ago. I've never used ADAT, but they seem more popular today.

That was interesting what cyrano said about UTP boxes from Appsys getting 32 channels. That sounds pretty damn versatile. But if you were to increase your sample rate, would that number go down?

5 Reply by ramses (edited by ramses 2022-12-25 20:26:20)

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Re: Why is s/pdif not so popular?

ADAT = 8ch@single-, 4ch@double-, 2ch@quad speed
SPDIF = 2ch @single - quad speed (44.1 - 192 kHz)
Simply two different protocols over the same type of link.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

6 Reply by mike G (edited by mike G 2022-12-25 20:38:18)

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Re: Why is s/pdif not so popular?

I have seen that chart you posted ramses. I just wasn't sure if that applied to what cyrano said about the UTP boxes from appsys. How is he getting 32 channels from ADAT unless he has 4 ADAT cables on his interface and he is running at 44.1 hz?
I would assume if he increased his sample rate to 48hz, he would only get 16 channels?

7 Reply by ramses (edited by ramses 2022-12-25 20:41:19)

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Re: Why is s/pdif not so popular?

single speed  = 44.1/48 kHz     = 8ch per ADAT port x 4 ADAT ports =  32 channels in total
double speed = 88.2/96 kHz     = 4ch per ADAT port x 4 ADAT ports =  16 channels in total
quad    speed = 176.4/192 kHz = 2ch per ADAT port x 4 ADAT ports =   8 channels in total

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

8 Reply by mike G (edited by mike G 2022-12-25 22:38:21)

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Re: Why is s/pdif not so popular?

Forgot to post something someone said at another forum when I was responding. He said " TOSLINK was often regarded as having higher jitter. The trouble I suppose is that while great for 16 bit, the spec was originally limited to 20 bits, later extended to 24 bit, with some compatibility issues, of course, between equipment." It sounds like all that's been fixed. Just wanted to mention it for sake of (myself) trying to understand how this rumor came about.

I was not aware that, as was explained somewhere:
---

  • A normal Toslink is the optical version of S-PDIF or ADAT and only two channels.

  • A lightpipe, although it uses the same cable, is capable of multi-channel.

TOSLINK is a connection type. It is the same for ADAT and optical S/PDIF. While ADAT and S/PDIF are not compatible, they can both use a TOSLINK connector and cable. There are devices that can put both ADAT *or* S/PDIF through their TOSLINK connector, but it has to be the correct format on both sides (either ADAT *or* S/PDIF).
Coaxial S/PDIF is S/PDIF with an RCA connector, non-optical. Same format, different connection type.

---

This was all new to me till just this morning.


Regarding the last chart ramses, looks good. Thanks

Speaking of light pipe, this -> https://www.researchgate.net/publicatio … ws-the.png is wild.

And this https://api.army.mil/e2/c/images/2012/0 … ax1200.jpg

  • ramses
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Re: Why is s/pdif not so popular?

TOSLINK is the connection type and you can run two types of protocols over this optical link (ADAT, SPDIF).
SPDIF protocol can also be transferred via copper -> coaxial SPDIF.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
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Re: Why is s/pdif not so popular?

Good to know ramses. Thanks brother
This stuff had my head spinning today

11 Reply by ramses (edited by ramses 2022-12-25 23:05:03)

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Re: Why is s/pdif not so popular?

While we are at it … SPDIF can also be transferred via AES (in consumer format).
Pinout of AES to SPDIF cable is documented in RME manuals.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

12 Reply by mike G (edited by mike G 2022-12-26 00:34:24)

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Re: Why is s/pdif not so popular?

ramses wrote:

While we are at it … SPDIF can also be transferred via AES (in consumer format).
Pinout of AES to SPDIF cable is documented in RME manuals.

That's the adapter setup I'm using that came with the UCX II. I'm running consumer SPDIF via the AES adapter connector. From what I understand, AES is kind of more or less an open interface-bridge. So it's not tied to any sampling rate or audio standard, but more like a way to interface all the different connector types mentioned above.

13 Reply by mike G (edited by mike G 2022-12-26 07:19:15)

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Re: Why is s/pdif not so popular?

One last thing. someone on another forum had asked me where I was getting my info from when I said that "Toslink only supported two channels." Even a google search says Tos only supports 2 channels. But now days Toslink is the connector for ADAT and it is NOT limited to two channels.

I found this link below that explains the history. Looks like you can transfer 8 channels with the Toslink, not just two. Not sure why everyone out on the net keeps associating Toslink with only two channels. Maybe it's the PCM aspect? The more I look into this the more I'm confused.

Here is a quote from the link below:

"The Toslink format had, until then, been used for carrying the stereo SPDIF digital audio format over optical cables. But Alesis adopted the format to deliver 8 channels of digital audio at 48K/24bit and was christened officially as the ADAT Optical Interface, and more commonly known at the time, as the ADAT Lightpipe."
https://www.pro-tools-expert.com/produc … at-is-adat

14 Reply by ramses (edited by ramses 2022-12-26 08:23:26)

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Re: Why is s/pdif not so popular?

See post #9.

TOSLINK is the "physic" … you can run two different protocols over it (ADAT, SPDIF).

SPDIF is the two channel protocol which supports up to 192 kHz.

ADAT protocol supports 8ch, but only at single speed (44.1/48 kHz) otherwise the bandwidth would not be sufficient.

Therefore, if higher sample rates are needed, ports are multiplexed to achieve the higher bandwidth requirements (of higher sample rates) per channel.
For double speed you need to "bundle/multiplex" two, for quad speed 4 channels.
Therefore, you have a variable number of ports with ADAT depending on the sample rate.

With SPDIF, where you have per protocol / design only two channels, the bandwidth is fully sufficient from single up to quad speed (44.1 - 192 kHz).

Please note, that RME uses TOSLINKs with a higher bandwidth in their products, which should be more or less the de-facto standard for studio products.
But this is not the case for every consumer product. Some have TOSLINKs built-in which support only a lower bandwidth, and by this only 96 kHz for optical SPDIF.

I had such an issue with an Oehlbach 4:1 TOSLINK switcher, where the vendor claimed on the package to support 192 kHz.
But it had the wrong TOSLINKs built-in with lower bandwidth and supported only 96 kHz.
Now is an Optosel 4:1 Mk II version out which supports 192 kHz.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

15 Reply by mike G (edited by mike G 2022-12-26 07:42:01)

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Re: Why is s/pdif not so popular?

That's a good point ramses.
I think people are mixed up talking about how many channels the connector supports when in fact it has more to do with the speed multiplexing as you mentioned that is the real factor.

And I think Toslink is what's used for ADAT as the connector right?

Thanks for all the help and support you've given.

  • ramses
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Re: Why is s/pdif not so popular?

Please re-read, I added information.
https://forum.rme-audio.de/viewtopic.ph … 15#p195315

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

17 Reply by ramses (edited by ramses 2022-12-26 07:44:39)

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Re: Why is s/pdif not so popular?

mike G wrote:

That's a good point ramses.
I think people are mixed up talking about how many channels the connector supports when in fact it has more to do with the speed multiplexing as you mentioned that is the real factor.

Thanks for all the help and support you've given.

I would say it the other way around, the multiplexing is a result of different protocols.
SPDIF is - like AES - a two channel protocol per design. ADAT a 8ch protocol (at single speed).

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

18 Reply by ramses (edited by ramses 2022-12-26 07:57:23)

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Re: Why is s/pdif not so popular?

The transmission of data has three things
Protocol header, data, a certain form of synchronization, either inside of the protocol or by using extra control wires.

The protocol header of SPDIF / ADAT are different, they are different protocols (over the same physic, TOSLINK).

Information about ADAT/SPDIF protocol, e.g. from here:
- ADAT https://ackspace.nl/wiki/ADAT_project
- SPDIF https://www.st.com/resource/en/applicat … ronics.pdf

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14

19 Reply by mike G (edited by mike G 2022-12-26 08:29:13)

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Re: Why is s/pdif not so popular?

Excellent example in post #14 and #9
And yeah, that was pretty shady regarding the Optosel 4:1 Mk II. I know some SSD manufactures do the same thing. Computer memory company's do the same thing advertising the transfer rates in the module name rather then the speeds because it sounds better. Never the less, that was a good example of how much the implementation matters.

By the way, ramses. Are you like an electrical engineer for RME?
Just curious. You seem like you know you're stuff. You do a great job explaining things for the common user. But something tells me you can really go deep into it. Some of this stuff can really be tricky when you brake things down to electrical theory and protocols themselves. Very interesting topic though. I've learned a LOT.

I find the db and dbv voltage stuff confusing when you get deep into it, but at the basic level, I do understand them enough to that I'm staying about 6db under 0 db for my line levels. 0 DBFS (fullscale) being the max bit's of a file. But man, I ran across some sweatwater page that started out simple and then lost me.
https://www.sweetwater.com/insync/speci … on-summit/

In any case, there's always room for improvement no matter what it is. My next venture is EQing and putting elements of a mix in their own space.  Never ends..lol

20 Reply by ramses (edited by ramses 2022-12-26 08:52:42)

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Re: Why is s/pdif not so popular?

This is simply my hobby. I learn a lot myself by explaining things to others.
Also about different products, vendors and why it is beneficial to invest into RME products.

BTW .. Maybe easier to understand:
https://www.sweetwater.com/insync/under … udio-gear/

And .. Sengpiel is a must, sry, english version of this page not available anymore:
http://www.sengpielaudio.com/Rechner-db-volt.htm

I added a screenshot of an excel sheet to this blog article (https://www.tonstudio-forum.de/blog/Ent … ses-EN-DE/):
https://www.tonstudio-forum.de/attachment/2915-overview-adi-2-dac-pro-dbu-auto-reflevel-ranges-snr-v002-jpg/
There you can see nicely the dependency between reference level, volume control, resulting SNR/dynamic range for the products ADI-2 Pro and DAC FS. This illustrates the benefits of the feature auto-reflevel of this product.
And also gives you the resulting values for, e.g.,  Voltage according to formulas on Sengpiels page.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
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Re: Why is s/pdif not so popular?

Lots of talk about AES, coax and TOS signal quality. Naturally they have always been compared, but I have yet to see some scrutinizing testing of these claims in a general sense.

ADI-2 DAC, ADI-2 PRO, DigifaceUSB, UCXII, ARC, HEGEL.h80, KEF.ls50, HD650, ie400pro _,.\''/.,_

22 Reply by mike G (edited by mike G 2022-12-26 09:25:29)

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Re: Why is s/pdif not so popular?

@ ramses
That's funny you posted this link
https://www.sweetwater.com/insync/under … udio-gear/

I was just reading that page before I checked your post. The other link got way too crazy so I had this easier one bookmarked.

Yeah, regarding RME. I did a LOooooooooooooooooooooooT of reading across different fourms to see what people were saying when comparing interfaces around the same price range. There are a few things that were very impotent to me and the deciding factor as to why I went with RME.

  • They support their products for a long time. They write drivers even for old products and utilize an open standard of drivers.

  • They have great sounding converters. Don't know about the pre amp, I have not even tested it yet, I have my John Hardy M1, but the converters are very transparent and natural sounding for this price range.

  • They write excellent software from everything I've read and it seems this IS the case in my experience so far

  • They are German, and Germans tend to make really good quality things, and I'm German..hehe..lol I've got a little Italian in my blood but I'm mostly German. Just kidding about that being a factor, but kind of being serious also. Germans tend to make great stuff

But regarding what I said about supporting their drivers. I was going to by from Apogee, their converters are great, but they discontinued support on almost all their middle of the line products and only seem to care about their high end Synthogy line. People spent $ hundreds to thousands of dollars on their products only to find out that they won't get driver updates. I will NEVER buy from them until they change their tune. I stand behind RME. They seem like a company that cares about their end users. Company's that discontinue support don't get my money. If a company is still in business there's no reason they can't write drivers or interfacing technology to keep something that someone loves running. Even if I have to pay for a driver update for a legacy piece of equipment I love, I would be glad to. But don't just drop support on your end users. Apogee is off my book.

@happy_amateur
You sound like you're about to get technical..lol
My recording engineer friend use to say that ADAT suffered from jitter, but that was like 25 years ago. I would imagine that the modern clocks improved some of that?

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Re: Why is s/pdif not so popular?

A few interesting information are collected in this article.

https://www.lowbeats.de/jitter-fakten/

I have the impression that this article is not too bad.

To the chapter "Die zehn wichtigsten Fakten"

to 7) if you have such an external player with a fix clock, then you can use it as clock master for a RME based setup as RME devices with SteadyClock [FS] technology are an ideal clock slave. Additionally RME products like ADI-2 Pro and ADI 2/4 Pro have a built-in SRC where you can isolate the fix clock and use for the rest of the environment the sample rate of your choice.

to 8) with RME it is solved by SteadyClock

to 9) clock is refreshed in RME products like ADI-2 DAC / Pro and ADI 2/4 Pro and the final D/A conversion is being performed with the internal FS clock, better is not possible.

BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14
  • cyrano
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Re: Why is s/pdif not so popular?

mike G wrote:

I have seen that chart you posted ramses. I just wasn't sure if that applied to what cyrano said about the UTP boxes from appsys. How is he getting 32 channels from ADAT unless he has 4 ADAT cables on his interface and he is running at 44.1 hz?
I would assume if he increased his sample rate to 48hz, he would only get 16 channels?

These Appsys boxes convert 4 ADAT IOs (16 channels) to one UTP cable. Intended for distances where optical can become a problem, eg between 15 and 80 meters.
See:

https://appsys.ch/en/products/extenders

The protocol over UTP isn't TCP/IP, it's just a smart electrical conversion to another kind of transport medium.

And you can also send MIDI, if you can spare one of the four optical inputs to do that. I've never used it though.

I also never use sample frequencies over 48 kHz, but that should be possible, halving the number of channels at every step, like Ramses explained.

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Re: Why is s/pdif not so popular?

ramses wrote:

This is simply my hobby. I learn a lot myself by explaining things to others.
Also about different products, vendors and why it is beneficial to invest into RME products.

BTW .. Maybe easier to understand:
https://www.sweetwater.com/insync/under … udio-gear/

And .. Sengpiel is a must, sry, english version of this page not available anymore:
http://www.sengpielaudio.com/Rechner-db-volt.htm

@ Ramses: I agree best audio links on the net

Check here...

http://www.sengpielaudio.com/Calculations03.htm

I think the web pages is translated here

best regards S-EH

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Re: Why is s/pdif not so popular?

Hi all

Late to the party…
S/PDIF (Sony/Philips Digital Interface) is more popular in the consumer / hi-fi world.
It not only can transport two PCM audio channels but also data streams containing multichannel streams (DTS, AC3, MPEG2). 
Interesting read here: https://www.epanorama.net/documents/audio/spdif.html

Regards, Oliver

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Re: Why is s/pdif not so popular?

The point about S/PDIF is special indeed. It is a rock solid protocol, easy to implement (nowadays even some microcontrollers use it) and as a "b1b2" code it has best options for clock recovery regarding the the number of transformed bits required.

To respond to the TO: I have no idea why not more gear is offered to use as "plugin" into the digital consoles. I am using S/PDIF for almost two decaded now to connect my self built gear. Moreover I established it as a transmission layer in industrial devices.

The S/PDIF's "brother" - the manchester code - has even been used to synchronize the electronics to control the magnets of particle accelerators effectively.

I am using it to transport MIDI data in between devices.