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Analogue audio via digital cables?

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Analogue audio via digital cables?

Postby Mike Senior » Tue Jun 18, 2013 6:34 am

Here's one for the techies -- my electronics knowledge has maxed out on it!

I recently bought a DB25 to eight-way TRS loom which purported to be for analogue connections, but when it arrived the multicore cable's external jacket was clearly marked "DIGITAL AES-EBU 110 OHM". Will this affect the analogue audio performance for line-level signals appreciably, and if so how?
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Re: Analogue audio via digital cables?

Postby John Willett » Tue Jun 18, 2013 8:50 am

110Ω digital balanced cable is fine for analogue audio - I use it all the time myself.

The AES3 spec was designed in the first place to use normal mic. cables - it's just that by using proper 110Ω digital balanced cable the digital signal will go about twice as far as on a bog standard analogue one.

So - yes - it's fine.
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Re: Analogue audio via digital cables?

Postby Mike Senior » Tue Jun 18, 2013 9:21 am

Great -- thanks John. That sets my mind at rest!
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Re: Analogue audio via digital cables?

Postby Goddard » Tue Jun 18, 2013 9:29 am

That cable itself is fine for either analog or digital carriage, and it's not uncommon to find AES/EBU digital cable being used for analog looms as well these days.

But if it is actually a digital loom (unlikely if it's using TRSs rather than XLRs) then watch out for the pin wiring on the DB25, as there are 2 different wiring schemes (pinouts) - the "TDIF" scheme (Tascam and Digidesign) which is pin-compatible with Tascam DB25 analog wiring, and the Yamaha scheme (also used by Mackie and Lynx amongst others) which is not pin-compatible with DB25 analog wiring.
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Re: Analogue audio via digital cables?

Postby Hugh Robjohns » Tue Jun 18, 2013 9:37 am

Mike Senior wrote:... the multicore cable's external jacket was clearly marked "DIGITAL AES-EBU 110 OHM". Will this affect the analogue audio performance for line-level signals appreciably, and if so how?


The only difference between bog-standard audio cables, and those optimised for AES3 digital audio is that the latter have a lower capacitance (and often better shielding) to preserve the wave shape of the digital pulses. AES3 has a fundamental frequency of 1.5MHz with lots of strong harmonics above that, and capacitance will kill those, resulting in reduced eye heights and jitter.

This reduced capacitance has no audible or measurable effect on the base-band audio, so you can use digital cable with analogue audio... and I do it all the time.

The only practical issue, normally, is that a D-sub break out intended for AES3 will have four male and four female XLRs since it carries four AES3 feeds in each direction, whereas D-sub breakouts for analogue will have eight XLRs of the same sex (male or female) as it carries eight channels in one direction only. In your case, with TRS plugs fitted, the point is moot.

By the way, the use of 25-pin D-subs for analogue and digital audio connections is now formally enshrined in the international standard AES59-2012, which is essentially the original Tascam standard but now fully documented and bolted down. The pin allocations (hot/cold/screen) for each channel is the same in AES59 whether the application is digital or analogue, and only the signal direction changes between the applications.

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Re: Analogue audio via digital cables?

Postby Hugh Robjohns » Tue Jun 18, 2013 9:50 am

Goddard wrote:But if it is actually a digital loom (unlikely if it's using TRSs rather than XLRs) then watch out for the pin wiring on the DB25, as there are 2 different wiring schemes (pinouts) - the "TDIF" scheme (Tascam and Digidesign) which is pin-compatible with Tascam DB25 analog wiring, and the Yamaha scheme (also used by Mackie and Lynx amongst others) which is not pin-compatible with DB25 analog wiring.

Actually, there were/are at least four different 'standard' pin outs for DB-25 plugs used for AES3 interfaces.

The original Tascam format was adopted by the likes of Digidesign and SADiE and is now the basis of the AES59 standard -- the only one that should now be used on new equipment.

Then there was the Yamaha format, which was adopted by Apogee, Mackie, Lynx and several others, as you say.

Euphonix had a third incompatible wiring format, and Genex added a fourth!

The very useful RME ADI-4DD digital format converter has moveable header plug inside which allows its external DB-25 socket to be reconfigured for either the Tascam (AES59), Yamaha or Euphonix formats.

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Re: Analogue audio via digital cables?

Postby Mike Senior » Wed Jun 19, 2013 2:02 pm

Thanks for the additional info and confirmation, Hugh!
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Re: Analogue audio via digital cables?

Postby Andi » Wed Jun 19, 2013 2:05 pm

Without standards all would be chaos; oh, hang-on a minute!
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Re: Analogue audio via digital cables?

Postby Hugh Robjohns » Wed Jun 19, 2013 2:19 pm

The audio industry loves its standards... that's why there are so many of them ba-dum-tish!

Thankfully, Tascam's bespoke standard for balanced analogue audio on 25-pin D-subs quickly became a de-facto industry-wide standard and is now finally enshrined permanently in AES59.

The allocation of AES channels on 25-pin D-subs was a nightmare, but sense has finally prevailed. It's a shame that there are so many Yamaha consoles out there with the now non-standard configuration, but hopefully the planet's manufacturers will converge now on the AES59 specifications which will make all out lives a lot easier in the years to come.

Shame it took the AES so long to pick up the reigns on that one, though. They really should have been pro-active rather than re-active in my view, but that's the way they seem to like to work.

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Re: Analogue audio via digital cables?

Postby Andi » Wed Jun 19, 2013 2:39 pm

Was it Groucho Marx "these are my principles, and if you don't lke them....well, I have others!"?

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Re: Analogue audio via digital cables?

Postby Hugh Robjohns » Wed Jun 19, 2013 3:00 pm

It was indeed!

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