Axe-FX II: SPDIF, AES/EBU and general digital I/O idiocy

swartzfeger

swartzfeger

Member
Gang, I'm really trying to avoid buying a new interface to go along with my new Axe-FX II. My Apogee Duet 2 is great -- solid preamps, very good conversion. I can never see needing more than 2 channels as I'll never be recording drums, recording more than a stereo acoustic, etc. The interface is virtually perfect for me except it doesn't have any sort of digital I/O.

The great thing I'm learning about the Axe is that 1) it has great converters and 2) can record via USB and both of those together mean I can avoid upgrading my interface for some time, but now I'm learning/reading that the Axe's USB audio out isn't 'free' in the sense that it does take a CPU hit. I can't say whether the presets I would create would/wouldn't be CPU hogs as I don't know how hard various effects and amps etc hit the CPU. That said, I'd like to avoid the CPU usage if I can.

Today, I realized (remembered) that Macs' 3.5mm audio inputs are also SPDIF... but looking on the back of the Axe, it looks like the Axe SPDIF is a RCA-style connector. If such a beast exists, is converting a spdif from RCA to 3.5mm 'reliable'? I'm guessing since it's digital and simple 1s and 0s, nothing's getting lost in the conversion, so to speak.

Also, I'm noticing on the I/O of a lot of products that not all SPDIF are the same, i.e., some are RCA style, and others are optical/toslink. I guess the same question applies. Is RCA<->optical reliable?

And another -- I'm thinking of getting a preamp (primarily for vocals) that could add some color as an instrument DI as well. Something like the Focusrite ISA One. Looking on the back of that (actually, the ISA's additional ADC card), it has SPDIF and AES. The AES appears to be a PC-like, trapezoidal 9 pin connector... but on the back of the Axe, the AES looks to be like some sort of round midi-style 3 pin connector. Ack, this stuff is so confusing.

My ultimate goal would be to do no conversion (use the Axe USB), don't hit the Axe CPU (don't use the USB) and not have to spend $2000 on a new interface like a Metric Halo ULN-2 just for digital I/O. I guess I could always buy a dirt cheap AI for just digital I/O and somehow create an aggregate device so the Duet still handles the conversion.

One last thing... I know Cliff has mentioned a few times (paraphrasing) that Axe's convertors are top notch -- are there any official specs on this and how they stack up against convertors out there? Are we talking Orpheus/Lavry etc or Mbox/Presonus or something in between.

Something's telling me I'm worrying waaaay too much about (one) conversion that could never ever be heard in a modern mix and just stfu and write and record, but if I can avoid converting a signal I'd like to be able to do that.

Not sure if this post was a question, soliciting advice, or an irritating whine. Thanks for any input. :)
 
simeon said:
huh? that's daft.
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Indeed. But I never saw myself using any sort of outboard gear, obviating the need for any kind digital I/O. Focusrite's Saffire Pro series has SPDIF at very affordable prices, so I'll research doing an aggregate AI w/SPDIF + Duet for conversion combo.
 
Stop worrying and just use the USB. The CPU hit is not going to be huge and unless you're creating some sort of crazy synth harmonizer patch you're unlikely to run into the limits of the Axe 2 CPU.
 
swartzfeger said:
Also, I'm noticing on the I/O of a lot of products that not all SPDIF are the same, i.e., some are RCA style, and others are optical/toslink. I guess the same question applies. Is RCA<->optical reliable?

And another -- I'm thinking of getting a preamp (primarily for vocals) that could add some color as an instrument DI as well. Something like the Focusrite ISA One. Looking on the back of that (actually, the ISA's additional ADC card), it has SPDIF and AES. The AES appears to be a PC-like, trapezoidal 9 pin connector... but on the back of the Axe, the AES looks to be like some sort of round midi-style 3 pin connector. Ack, this stuff is so confusing.
Click to expand...

S/PDIF and AES/EBU are sligtly different digital protocols, doesn't really say anything about how they are transferred. Most common is RCA and toslink termination for S/PDIF and XLR for AES/EBU though. The 9-pin d-sub on the ISA-card is probably just for a breakout-cable.

You can't go from coaxial to optical (Axe - Mac), unless you go through some thingy that convert the electrical signal to an optical one.
 
Thanks Trazan, very helpful. As laxu said above, I probably won't worry about it and jut go USB, but I do like to geek out when it comes to thinking about these things. The TC Electronics Impact Twin has both RCA and optical I/O and is affordable at $369 US, so there are options out there if I need them.
 
There is a device out there that converts OPTICAL to COAX with no protocol intervention. I believe it's called a CO3 (I have one down in the studio) and is made by M-Audio or someone like that. I have used it successfully in a number of applications, but have not tried it with the AXE FX II. I have recently seen some on e-Bay, but don't know if they are still in production.

BTW - as an aside, remember that all digital I/O on the Axe-FX II is done at 48Khz - no alternative. I stopped using the USB as a result, and take the AXE's outputs into my Fireface 800, as I do with my DI box (Radial J48). Sounds fine, even though there is one extra D/A -> A/D conversion cycle.

Pete
 
Just so you know - Saffire's have to be set as the master clock in order to communicate via Spdif. If you want to use the Spdif as an output on Axe-fx II it has to be the master clock. So you can't use the Axe-fx II with Spdif if you are running a Focusrite Saffire interface.
 
Trazan said:
S/PDIF and AES/EBU are sligtly different digital protocols
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This is true, but AES/EBU and SPDIF are close enough that sometimes a simple XLR -> RCA adapter works (there's an impedance mismatch which may or may not introduce jitter, depending on how well the chipsets in the two devices get along). If not, then the cheapest converters that I'm aware of (after searching for less time than it's taking me to write this post) are both around $90 from B&H (and they both go both ways, which adds costs that aren't needed in this case): AES/EBU <-> RCA and AES/EBU <-> Optical.

Trazan said:
You can't go from coaxial to optical (Axe - Mac), unless you go through some thingy that convert the electrical signal to an optical one.
Click to expand...
Yep. I found this RCA -> Optical adapter for $20.

(Note that this means that if you're lucky, you can go from AES/EBU -> Toslink for $20 plus the cost of an XLR -> RCA adapter and cabling.)

Incidentally, the cheapest USB audio interface with a SPDIF input that I could find is the Lexicon Omega Desktop Recording Studio for $150.

Oh, and I have no experience with any of these products, so I can't vouch for their quality or anything.
 
TheOtherDave said:
This is true, but AES/EBU and SPDIF are close enough that sometimes a simple XLR -> RCA adapter works
Click to expand...

Yeah, S/PDIF -> AES/EBU with often work fine with just an RCA -> XLR cable. Not sure about the other way around though, as p-p voltage of the AES may be more than 10 times that of S/PDIF!
 
Speculum Speculorum said:
Just so you know - Saffire's have to be set as the master clock in order to communicate via Spdif. If you want to use the Spdif as an output on Axe-fx II it has to be the master clock. So you can't use the Axe-fx II with Spdif if you are running a Focusrite Saffire interface.
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Thanks! That's why I love this site -- I had never considered the master/slave aspect of SPDIF. Having just looked at Focusrite's website, they don't advertise this on their Saffire Pro pages. And prospective buyers probably wouldn't find out until they bought the unit or downloaded the pdf manual. The Saffire Pro at most would be a lateral move compared to my Duet and probably has (negligible) inferior conversion. TC Electronic's Impact Twin looks great on paper (I know, I know) spec-wise and seems to fare extremely well in this AD/DA loop test.

Thanks for the heads up -- I now know to read more than just the marketing pages for products and read the actual manuals.

plyall said:
There is a device out there that converts OPTICAL to COAX with no protocol intervention. I believe it's called a CO3 (I have one down in the studio) and is made by M-Audio or someone like that. I have used it successfully in a number of applications, but have not tried it with the AXE FX II. I have recently seen some on e-Bay, but don't know if they are still in production.

BTW - as an aside, remember that all digital I/O on the Axe-FX II is done at 48Khz - no alternative. I stopped using the USB as a result, and take the AXE's outputs into my Fireface 800, as I do with my DI box (Radial J48). Sounds fine, even though there is one extra D/A -> A/D conversion cycle.

Pete
Click to expand...

re: 48Khz -- yes, knew that. No problem with that, although I can see how that may cause minor fits for other's and their workflows. My setup is pretty simple, although I've tons of sample libraries and I'm positive a good bit of them are at 44.1.

Radial J4? No fair! :razz

re: converting from RCA <-> optical... knowing nothing about clocks and jitter, I've got to wonder if something get's jumbled? I always assumed digital was simply (and always) just 1s and 0s, but now I'm not so sure.

I'm tempted to ask about the Axe's clock (per Speculum's note that the Axe must be set as the master), but I think it'd start going over my head.
 
No worries. I use a combo of USB and analog routing for reamping, sending line signals for fx, etc. and there doesn't seem to be any problem at all. It's a bit more wonky on stereo signals, but it ends up working out. The saffire pro line also has some pretty good mic pres, but I do use my Focusrite ISA One more often.
 
My AXE FX gets here Tuesday but I've already started reading a lot around here and fellow PT fan swartzfeger asked some great questions that help me as well. However my situation is a bit different.

I am using a MOTU Track16 (LOVE IT) via USB with ASIO drivers into Sonar X2. So far so good. Now if I use USB for the AXE FX, aren't I limited to only one interface at a time due to ASIO limitations ? I have an optical SPDIF in on the Track16 so would it make sense to connect the AXE to it via SPDIF ? Of just run audio line in via the Track16 ?

All help GREATLY appreciated and hopefully I didn't hijack your thread, swartzfeger :)
 
Gregmang said:
My AXE FX gets here Tuesday but I've already started reading a lot around here and fellow PT fan swartzfeger asked some great questions that help me as well. However my situation is a bit different.

I am using a MOTU Track16 (LOVE IT) via USB with ASIO drivers into Sonar X2. So far so good. Now if I use USB for the AXE FX, aren't I limited to only one interface at a time due to ASIO limitations ? I have an optical SPDIF in on the Track16 so would it make sense to connect the AXE to it via SPDIF ? Of just run audio line in via the Track16 ?

All help GREATLY appreciated and hopefully I didn't hijack your thread, swartzfeger :)
Click to expand...

No worries, Greg!

I'd say connect via SPDIF if you can, but via analog would be fine too. Try both. I think SPDIF may only make a slight difference when it comes to reamping, but I can't say for sure because like you, my Axe isn't here yet (not even ordered yet!)

ASIO limitations -- I can't speak to this as I'm a Mac guy. I know in OS X, I can create an aggregate audio device, i.e., I can link my Duet 2 with another interface via software and (ostensibly, I think) use one interface as I/O and another and another for conversion, etc. It works in theory as I've read many people have had great success with aggregate devices, and others have flakey performance (don't know if this is driver conflicts with OS X's Core Audio or what).

Not sure if there's an ASIO equivalent to an aggregate audio device.
 
Speculum Speculorum said:
Just so you know - Saffire's have to be set as the master clock in order to communicate via Spdif. If you want to use the Spdif as an output on Axe-fx II it has to be the master clock. So you can't use the Axe-fx II with Spdif if you are running a Focusrite Saffire interface.
Click to expand...

Is this something that occurs only in an aggregate setup? To use SPDIF input as clock source, all that should be needed is changing sync source from Internal to SPDIF in the mixer software.
 
Speculum Speculorum said:
Just so you know - Saffire's have to be set as the master clock in order to communicate via Spdif. If you want to use the Spdif as an output on Axe-fx II it has to be the master clock. So you can't use the Axe-fx II with Spdif if you are running a Focusrite Saffire interface.
Click to expand...

You sure about that? Having an S/PDIF input...surely one must be able to select it as sync source?
 
Bakerman said:
Is this something that occurs only in an aggregate setup? To use SPDIF input as clock source, all that should be needed is changing sync source from Internal to SPDIF in the mixer software.
Click to expand...

Yeah, that's what I thought to. I'm set up to have my Axe-fx II running as my input and my Saffire to run as my output. If I set up an aggregate device I can get wet or dry signal through the Spdif, but I can't make a dry or line-level signal run out to the Axe-fx II through Spdif because I just keep getting the "No input clock" message. So if I want to use the Axe-II to reamp (like I do with all my bass recordings) or as outboard gear it just won't work, therefore it is useless to me. Also, if I remember correctly no sound comes out of my speakers no matter what because both machines are vying for mastering the clock. Go figure.
 
Speculum Speculorum said:
Yeah, that's what I thought to. I'm set up to have my Axe-fx II running as my input and my Saffire to run as my output. If I set up an aggregate device I can get wet or dry signal through the Spdif, but I can't make a dry or line-level signal run out to the Axe-fx II through Spdif because I just keep getting the "No input clock" message. So if I want to use the Axe-II to reamp (like I do with all my bass recordings) or as outboard gear it just won't work, therefore it is useless to me.
Click to expand...

With SPDIF one way from Axe to Saffire, everything works, including being able to select SPDIF as sync source in MixControl? Good so far if true.

To use the Axe SPDIF input, the Saffire needs to be master. Once you choose SPDIF input on the Axe, it uses (or waits for) a signal to use as the clock source.
 
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