AES cable used for Analogue Audio. Is this a bad thing to do?

[majickal]

Hi All,

This is my first post here and I wanted to ask a few questions of the community that have been widely discussed in my workplace regarding the differences between using 110 ohm cable and 600 ohm cable for microphone and line level signals.

Q: Firstly, is it OK to use AES/EBU 110 ohm balanced cable to pass a) line level signal b) microphone level signal, rather than 600 ohm microphone cable?

Q: Are there any implications for running (what is known in the audio industry as phantom power) +48v over the 110 ohm line?

Q: Should we expect to see a drop in dynamic range if 110 ohm cable is used to pass an analogue signal rather than a 600 ohm microphone cable?

Q: With regards to cable capacitance and signal integrity, which is the better choice for both microphone and line level signal?

Q: Are there any reasons other that those mentioned above that may suggest that running line level and microphone level signal over a 110 ohm cable is a bad idea?

Q: Can we expect any sort of artefacts to be present in an audio signal if it is transmitted over a 110 ohm cable?



http://recordmixandmaster.com/2010-02-mic-line-and-instrument-level-whats-the-difference"

[/PLAIN]
Line Level

Line level signals have a much higher voltage output than mic or instrument level, usually somewhere around 750 millivolts. As this signal is stronger it can be carried over a longer distance. 750 millivolts is the industry standard and allows for the interconnection of different devices from different manufacturers.

There are two types of line level:

consumer line level is at -10dBV
professional line level is at +4dBu (or dBm)

[/PLAIN]
Mic Level

When sound hits the diaphragm of a microphone very low voltage signals are produced. On a dynamic microphone these signals are typically around 1.5 millivolts. For a more sensitive microphone the voltage would be more like 70 millivolts.

Mic level is -56 to -40 dbm.

Whilst there are a number of questions, I am really struggling to get to the bottom of this.
I have read and been told that there is no problem using 110 ohm cable for microphone level and line level applications.

However, I have also head, from one source, that is is a massive "no no" and under no circumstances should this be undertaken.

I do hope someone will be able to provide me with some insight into the matter, so I can get a definitive answer and put this one to bed, once and for all.

Best Regards

m :)

 

[jsgruszynski]

Generally mixing impedances is not a good idea. The original technology was specified to have matching source, cable and load impedances for maximum power transfer. Mismatching will affect things like amplitude levels, dynamic range, etc. and could also introduce reflections depending on the cable length.

Now whether these degradations apply to the specific equipment you are using in a specific recording scenario, is beyond the scope of this forum. The analysis is potentially very involved and labor intensive.

These are probably better questions for your cable, microphone and equipment vendors. They probably answer these questions every day and may even have application notes published that address it.

 

[majickal]

Hi jsgruszynski,

Thanks for the reply, I have heard some of the thing you have mentioned, noted on other forums.

Interestingly the cable manufacturers say there is no problem running mic or line level over AES cable, also, my experience in doing just that yielded no audible signal degradation.

Many of the forums I have looked at, specifically around this question, do not seem to have a definitive answer either way, in fact most responses were in support of using such cable for mic and line level.

I guess I will keep hunting to see if I can find out once and for all where the issues lie.

Thank you for your response, I really appreciate it and will use the information you presented to further research the question.

Best Regards

M

 

[dlgoff]

As jsgruszynski said,

Generally mixing impedances is not a good idea. The original technology was specified to have matching source, cable and load impedances for maximum power transfer. Mismatching will affect things like amplitude levels, dynamic range, etc. and could also introduce reflections depending on the cable length.

For a little more on this,

As a general rule, the maximum power transfer from an active device like an amplifier or antenna driver to an external device occurs when the impedance of the external device matches that of the source. That optimum power is 50% of the total power when the impedance of the amplifier is matched to that of the speaker. Improper impedance matching can lead to excessive power use, distortion, and noise problems. The most serious problems occur when the impedance of the load is too low, requiring too much power from the active device to drive the load at acceptable levels. On the other hand, the prime consideration for an audio reproduction circuit is high fidelity reproduction of the signal, and that does not require optimum power transfer.

http://hyperphysics.phy-astr.gsu.edu/hbase/audio/imped.html"