Educate me: AES cabling

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Matt Vivlamore

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Jan 11, 2011
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I’ve never looked into AES cables before and I have some products that can use the Digital AES (3pin).

What’s the difference between AES/EBU and DMX cable?

Are the XLR connectors different than the standard Mic XLR(NC3FX/NC3MX)?


Also, what will happen if I use regular Mic XLR cable while using all AES-XLR connections?
 
Re: Educate me: AES cabling

What’s the difference between AES/EBU and DMX cable?

Nothing as long as the cable is 110ohm cable, you're good

Are the XLR connectors different than the standard Mic XLR(NC3FX/NC3MX)?

Nope.. Same connector


Also, what will happen if I use regular Mic XLR cable while using all AES-XLR connections?

Not sure, I've only used the right stuff...
 
Re: Educate me: AES cabling

Mic cable is typically 75ohm, AES is 110. DMX is also 110 ohm, so you can use the same cable for either. Connectors are the same for all of them.

If you use regular mic cable it will probably work fine, up to a certain distance, at which point you'll have issues. The problem is that that distance can change, so what doesn't cause problems one day might the next. It would be best to use 110 ohm cable, and it's not super expensive. You can use 110 ohm cable for normal mic or line level signals, just not the other way around.
 
Re: Educate me: AES cabling

Shane Presley said:
Also, what will happen if I use regular Mic XLR cable while using all AES-XLR connections?
Click to expand...

For short patch, nothing. The impedance mismatch will mean your signal quality will degrade, but because this is a digitally encoded signal, signal degradation just means a lower transmission distance before errors, but it won't degrade the audio quality.

Lots of mic cable these days is in fact 110Ohm, since manufacturers realise that people like to have their mic & AES cable be interchangeable, and it makes no real difference to mic signals.

Once you start wanting to send AES a long way though, cable type matters a lot more, since there are practical differences between cables, other than just their impedance. It becomes important to look at the manufacturers spec. Not all AES cable is created equal.
 
Re: Educate me: AES cabling

Yup; Kevin is right, Brian is wrong: 120ohm.

I suspect you're ok unless you're pushing the length limits
 
Re: Educate me: AES cabling

There are two issues with DMX cabling - nominal impedance and capacitance. The latter matters less below 60mF, but is important to keep as low as possible, preferably less than 30mF. DMX is designed around a standard which is tested for 100 and 120 ohm connections. 110 is between the two and should behave perfectly fine.
 
Re: Educate me: AES cabling

Did I ever tell you all about wandering the world when I was young.

Occasionally we would have battles in which I did quite well.

I used a Nanochou which is 1000 times stronger than a Picochou.

Sent from my DROID RAZR HD
 
Re: Educate me: AES cabling

Shane Presley said:
What’s the difference between AES/EBU and DMX cable?

Nothing as long as the cable is 110ohm cable, you're good

Are the XLR connectors different than the standard Mic XLR(NC3FX/NC3MX)?

Nope.. Same connector


Also, what will happen if I use regular Mic XLR cable while using all AES-XLR connections?

Not sure, I've only used the right stuff...
Click to expand...

50, 75, 110, 600, is not cable. It is the terminating resistance at the receiver side of a connection. You would need a long cable to add up to 110 ohms.
Wiki states it this way with a 75 ohm Video definition -

Electrical termination of a signal involves providing a terminator at the end of a wire or cable to prevent an RF signal from being reflected back from the end, causing interference. The terminator is placed at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match AC impedance and hence minimize signal reflections

Cable does resist a signal, called impedance, depending in its length, thickness, capacitance and frequency being transmitted.
Capacitance is more of an issue for high frequency transmission than the resistance.

Cable is designed for the signal you are transmitting. But 1, 10, 100, 350, 1000Mhz can be moved on a coax, or a twisted pair.
 
Re: Educate me: AES cabling

Glenn Adams said:
50, 75, 110, 600, is not cable. It is the terminating resistance at the receiver side of a connection. You would need a long cable to add up to 110 ohms.
Wiki states it this way with a 75 ohm Video definition -

Electrical termination of a signal involves providing a terminator at the end of a wire or cable to prevent an RF signal from being reflected back from the end, causing interference. The terminator is placed at the end of a transmission line or daisy chain bus (such as in SCSI), designed to match AC impedance and hence minimize signal reflections

Cable does resist a signal, called impedance, depending in its length, thickness, capacitance and frequency being transmitted.
Capacitance is more of an issue for high frequency transmission than the resistance.
Click to expand...

Unfortunately the Wiki you quoted contradicts your assertion. The cable does have a characteristic impedance that does include capacitance, and the transmission line needs to be terminated to that impedance. If the input is self terminating no terminator is needed, but you cannot use "T" connectors to continue the signal run as the line will be multi terminated. If you can use T connectors the inputs are high impedance and a terminator must be used at the end of the line.

In the case of AES audio run, the inputs are generally terminating, and each input requires a dedicated source, you may not daisy chain AES signals.

The characteristic impedance of a cable is it's actual impedance over a predetermined length and includes all the elements of impedance R, L, and C.

For reliable operation AES3 balanced digital audio needs a twisted pair of 110Ω characteristic impedance, like CAT5, or DMX. AESid which is transmitted over coax requires 75Ω coax

You can find more information HERE or HERE.

Mac
 
Re: Educate me: AES cabling

A nice way to think about the characteristic impedance of an (ideal, lossless) transmission line is that it is the resistance you would see if you connected an Ohmmeter to one end of an infinite length of the line. And for an ideal line this is indeed a pure resistance, with no reactive component.

If such a line is terminated at any point in a pure resistance equal to the line's characteristic impedance, the impedance seen at the driving point remains unchanged. How are we to know, looking at the input, that there isn't just an infinitely long line out there beyond the terminator?

Real world lines have imperfections and losses which, in general, are a function of frequency. This loss per length is the principal property we look at when using coax to hook antennas to wireless gear.

As an aside, I got curious the other day and measured the characteristic impedance of the pairs in my Whirlwind mic snake and they came in right around 75 Ohms.

--Frank
 
Re: Educate me: AES cabling

mackerr said:
Unfortunately the Wiki you quoted contradicts your assertion. The cable does have a characteristic impedance that does include capacitance, and the transmission line needs to be terminated to that impedance. If the input is self terminating no terminator is needed, but you cannot use "T" connectors to continue the signal run as the line will be multi terminated. If you can use T connectors the inputs are high impedance and a terminator must be used at the end of the line.

In the case of AES audio run, the inputs are generally terminating, and each input requires a dedicated source, you may not daisy chain AES signals.

The characteristic impedance of a cable is it's actual impedance over a predetermined length and includes all the elements of impedance R, L, and C.

For reliable operation AES3 balanced digital audio needs a twisted pair of 110Ω characteristic impedance, like CAT5, or DMX. AESid which is transmitted over coax requires 75Ω coax

You can find more information HERE or HERE.

Mac
Click to expand...

I didn't say T tap. You better read it again.
 
Re: Educate me: AES cabling

Glenn, DMX is supposed to be transmitted over cabling that complies with the RS 485 serial specifications. In fact, DMX is pretty much a type of RS 485 serial interface. For these signals to reliably transmit, they require a certain set of electrical characteristics. Part of that is termination at each end of the chain, which is a 120 ohm (± a few) resistor, or in the case of interference, two 60 ohm resistors and a capacitor in the middle to create help filter the interference out. Either way, that is the ONLY way it is allowed to be terminated. Also, a chain is the only topology supported by RS 485, which is why splitting has to be done optically, which then gets sent out the split chains. This is all for the purpose of eliminating reflections.

Now - the cable itself also must have a certain characteristic impedance and capacitance within a set specification for the signal to be sent without degradation over a distance. This is why AES audio and DMX control needs particular cable - if the resistance by the cable presented to the driver isn't appropriate, the signal will distort (usually due to clipping). The capacitance degrades the signal itself, since the frequency of the signal may be too high for the cable to respond quickly enough. Personally, I think this is a more real issue with using improper cabling, especially over long distances. DMX data is transmitted at a frequency of 250kHz, and is basically a square wave. It won't look right on the other end through a mic cable.

Also, I've been reading through this TI paper on RS485: http://www.ti.com/lit/an/slla272b/slla272b.pdf
 
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