Music and XLR cables – Part 3

Marshall Chasin
June 5, 2012

This is the third in a series of blogs outlining some of what we know about optimal music recording.  When reading through these blogs one should be struck that we really know everything we need to know already when it comes to recording.  In some cases, what was learned in our first year audiology class provided “obvious” recording cues (such as ensuring a wide bandwidth) and in other cases, the information and concepts have been learned but may have applied to other fields than music recording.

The third question concerning recording musical instruments is which cable to use.  Now before your eyes start to roll up in your head, cables that connect the microphone to the recorder are important.  And they have great names such as RCA and XLR.  Where else in the field of audiology can we say the phrase, “XLR cable”?  Its use will guarantee that you will become the center of attention at your next party.

From the previous blog we discussed the differences and similarities between dynamic microphones and condenser microphones.  Condenser microphones require a power source and this can be a battery or a more remote source of power such as “phantom power” from the recorder itself.  Condenser microphones frequently use XLR cables.

Enough suspense!  XLR connectors for cables are characterized by three pins that are arranged in a triangular formation- two carry the signal and the third is the “hot” pin which supplies the power, and that’s why they are called XLR cables…. Well, not really.

The history of XLR cables is a bit more romantic.  Once upon a time Canon came out with a three-pin connector that was ideal for this use called the X connector, but the pins kept bending over in the receptacle.  Some brilliant design engineer filled in the receptacle with Rubber, leaving room for the three pins.  This improved things dramatically but in busy and rushed situations, the connector pulled out of its receptacle.  The solution was a Latch that improved the connection. And that is what the XLR mean in an XLR cable.

I know that you are quite excited about learning about the history of the XLR cable but that’s only the beginning.  The XLR cable can be connected to two sources- a low-impedance source and a high-impedance source.  This has implications for how long a cord you can get away with.  If you are recording something that is only several meters away from the recorder, there is no real difference between a high- and low-impedance system.  Many high-impedance systems are also called “balanced” and a feature of a balanced system is that you can use a 100-meter long cable or a 1-meter long cable and there will be no significant difference in the recording.  The same would not be the case with a low-impedance (unbalanced) system.  The 100-meter long cord would significantly degrade the signal in this case.

If you check the internet (an amazing source of incorrect information), there are many statements that a balanced high-impedance system is less noisy than a lower-impedance unbalanced one (such as one that uses ¼” jacks).  This is an urban myth.  There is no evidence that one is less noisy than the other- perhaps a secret plan by the manufacturers of XLR cables connectors?

Many recorders have a jack with ‘Hi-Z” written on it- this is the high-impedance balanced jack.  Other XLR jacks without this label may or may not be high impedance- you need to read the owner’s manual to get this information.

And to complicate things, if you looked at the connector panel on any audio-digital interface (which is the box that receives input from a microphone(s) on one side, and plugs into a digital recorder (such as your computer) on the other side, some connectors look like XLR connectors but also have a ¼” jack receptacle in the center.  These versatile jacks can receive both ¼” jacks and XLR connectors, but unless it says “Hi-Z” or “balanced” be careful about the length of your cable.

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