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Configuring Balanced Audio Input for Capture Appliances
Last Updated: Feb 26, 2018 11:27AM EST

This article applies to:  Echo360 Admins

The balanced audio input on both the Echo360 PRO and Echo360 SCHD appliances use a five-pin Phoenix connector to provide a professional grade audio connection with flexible wiring options. However, improper wiring of the connector can lead to a variety of auto problems in the processed capture, including silent mono audio files (while stereo audio sounds fine) as well as audio in only one channel (one ear of your headphones, or only one of two speakers).

To avoid audio problems in the future, and to provide better instruction for checking or changing your current audio input configuration, the topic below covers how to properly wire the Phoenix connector for balanced audio input as well as how to avoid the phenomena that cause silent and single-channel audio files.

Wiring the Phoenix Connector

The Phoenix connector on the back of both the PRO and SCHD appliances contains five slots for two differential pairs. They are:

  • Left Positive (L+)
  • Left Negative (L-)
  • Ground (GND)
  • Right Positive (R+)
  • Right Negative (R-)

The below figure shows the balanced Audio inputs on the back of the Echo360 PRO appliance.

Balanced audio input on the back of the PRO

See Microphone Input on the Echo360 POD below for information on the single-ended stereo input on the POD appliance.

Stereo wiring

A stereo connection to the balanced audio input should use separate wiring for the left and right channels.

The left differential audio cable pair should be connected to the L+ and L- pins, and the right differential audio cable pair should be connected to the R+ and R- pins. The middle ground pin should be connected to the cable ground, which is usually the sheath.

If your stereo audio cable does not have two differential pairs it is not a balanced audio source and should be connected to the RCA input jacks. Care should be taken to ensure the + and - terminals match the cable's description.

The below diagram shows proper stereo Phoenix connector wiring.

Stereo Phoenix Connector Wiring

The below figure shows a example picture of the differential pin-out of an XLR audio cable with the pins/slots labeled for both the male and female

Example Differential Pin-Out of an XLR Audio Cable

Mono Wiring

Most microphone systems output single channel (mono) audio. This can be connected to a single channel pair on the Phoenix connector (L+,L- or R+,R-). However, when using this wiring option, stereo audio files will have audio in only one channel (resulting in playback in only one ear of headphones).

To avoid this, you may want to connect the mono output to both channels of the balanced connector. In this case the positive signal should be connected to both the L+ and R+ inputs and the negative signal should be connected to both the L- and R- inputs. The single ground/sheath should be connected to the GND input.

The below diagram shows mono Phoenix connector wiring. This generates mono audio output but because audio captures are processed for stereo, will result in audio playback over a single channel, a noticeable problem in headphones.

Mono Phoenix Phoenix Connector Wiring

The below diagram shows mono-to-stereo Phoenix connector wiring. This generates mono audio output that is properly processed as stereo and provides audio playback in both channels (though it is the same in both and is not "true" stereo).

Mono-to-Stereo Phoenix Connector Wiring

Microphone Input on the Echo360 POD

The microphone input on the Echo360 POD appliance is a single-ended stereo input that can suffer from the same phase cancellation issues as the balanced audio input if not configured correctly.

The problem actually occurs because the POD has a single 1/8" RCA input jack, and both balanced and single-ended microphone plugs LOOK the same.

If a balanced output microphone is connected to a POD's microphone input, the resulting connection will have the + connected to the right input and the - connected to the left input or vice versa. This results in normal stereo audio files but silent mono files, due to phase cancellation.

If the microphone you are using has balanced-output capability, be sure you select the R/L or single-ended option before using it with an Echo360 POD.

Wiring Pitfalls

One of the most widely known pitfalls of balanced audio wiring is phase cancellation. When mono audio sources are incorrectly connected to the balanced audio input you could end up with perfectly usable stereo audio files, but silent mono files. This is because the mono source is connected to the balanced audio input with the phases reversed, which results in phase-canceled audio after mixing down to mono.

There are two ways for this to happen with a mono source:

  • In the first scenario the cable is connected to the Phoenix connector with the pairing swapped where one cable is connected to the L+ and R- inputs and the other cable is connected to the L- and R+ inputs.
  • The second scenario has the balanced cable connected to the R+ and L+ inputs.

To avoid this, be certain your bare wire audio configuration matches that shown above.

For more information on details, causes and effects of audio phase cancellation take a look at the following YouTube video: https://youtu.be/_N0ER4A73QE

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