Guide for setting up external devices

Supported Hardware


Manufacturer Protocol Notes
Allen and Heath USB Audio  
Arrikis USB Audio  
AXIA\Telos RTP\Livewire  
M-Audio USB Audio  
Scarlette USB Audio 6i6
SoundCraft USB Audio  
Stellar Labs\USB XLR USB Audio PCM2902 chipset


Manufacturer Protocol Notes
Black Magic HDMI  

Please Report successful manufacturers of hardware devices that are not listed

USB XLR adapter

NB: Line level input signal (+4dBu) will require attenuation by -15db to -20dB.

 USB XLR Adapter

The USB XLR Adapter uses the Texas Instrument PCM2902 chipset, detailed specifications for which may be found here.

600 ohm in-line XLR attenuators (-20dB) are recommended for installation in +4dBu radio broadcast chain.

When the USB to XLR cable is connected, both input and output may be routed through balanced XLR connectors. When using the inputs on the adapter for audio bypass, source programming is muted during playback of alert messages. After the message completes, source programming resumes.

To use the XLR cable with the Alert Player:

Connect the cables

  1. Connect the USB end to any one of the USB ports on the Player unit. The adapter MUST be connected before_power up for the system to auto-configure the adapter.
  2. Connect the male XLR output connectors to the inputs of your sound board, transmitter or switching relay.
  3. Connect the female XLR input connectors to the output of your audio source. Use in-line attenuators (-20dB) on the inputs if connecting to +4dBu line level audio sources.

Configure Audio

  • On the Outputs Tab, set audio output mode to PULSE. Disable the Test Signal From Sources__Tab enable the __Audio In Source setting audio mode to PULSE.

  • If using the GPIO switching Relay, connect a serial cable from the Player to the Switching Relay. On the Emergency Alerts tab, under Advanced Settings, enable the RS-232 DTR Alert signal. The RS-232 Device Filename should be set to the serial port (/dev/ttyS0 for Port 1, /dev/ttyS1 for Port 2).

    When audio mode settings are changed, reboot. Once rebooted, audio slider controls will be present in the dashboard under PULSE to set input and output levels.

 Input Source

Restart the Player

If no audio output is heard, refer to Troubleshooting.

Improving Sound Quality

When using USB sound cards, there are three aspects of the audio signal quality that must be addressed. To achieve the best possible sound quality, each of these limitations must be addressed in the configuration:

Signal Attenuation

The USB-XLR adapter is designed for input at -10dBv (0.316V, or 316 mV). Transmitter feed signals are typically +4Bu (1.228V). The difference, in dB, between +4 dBu and -10 dBv is -11.78 dB, or about -12 dB. Therefore, between 10dB and 20 dB of attenuation is recommended to avoid distortion of +4dBv input signals.

In-line attenuators are available Here.

 XLR Pad

Instructions for DIY “H” or “T” pads may be found on the DIY-Maker-Space-Broadcast-Projects.

Signal Phase

The INPUTS on the USB-XLR adapter are wired are out of phase, causing a muffled or variable output signal. The photo below shows the wires in the original configuration. To fix, you will need to swap wires to pins 2 and 3 (i.e the red and white wires) in ONLY ONE of the female XLRs. This will require solder and a soldering iron. After swapping, the white wire would be connected to Pin 2, and the red wire to Pin 3.

 XLR Pins  XLR Pins

Signal Delay

The USB-XLR adaptor introduces a signal delay of ~ 0.5 sec. To overcome latency delay, it is necessary to use a switching relay that interrupts the source signal to inject an Alert Message.

Mechanical RS232 Switching Relay

Switching relay is not dependant on the Alert Player for functioning. In the event of power failure continues to pass thru the source signal (however, relays require power to be able to switch to the Alert feed). Configuration of the Alert Player to issue GPIO DTR signals to the relay are covered in Getting Started.

 Relay Box


Update Alert Player. Com Port(s) are enabled in BIOS (default=on)

Install Relay

 Ports Diagram Screenshot

Connect DB9 connector (female) to Com Port 1 (ttyS0) on the back (left) of player.

  1. Connect XLR Audio Program Feed to studio out or source material

  2. EAS Switched Output to main output to STL and transmitter. Audio should normally pass through, unaltered.

  3. Connect EAS audio output from player into the XLR Female marked EAS Alert Feed using Male XLR-USB cable or onboard audio 1/8” mini jack.

Energize Power Supply

Configure DashBoard

Changes required for default settings.

  1. Audio Source> Uncheck Enable Audio In Source

  2. Emergency Alerts>Advanced Settings Check Trigger RS-232 DTR on Alerts


Inject test alert, mechanical relay will engage when alert plays and resume normal pass through when complete.

LED Scrolling Sign


Update alert player. Com Port(s) are enabled in BIOS (default=on)

Install LED Screen

  1. Connect DB9 Female to RJ12 connector to Com Port2 (ttyS1) on the back (right) of player.

  2. Plug RJ12 cable into adaptor and into LED Sign

  3. Sources Tab> Check Enable LED Screen

  4. Plug in AC power to sign. Start up message will scroll.

 LED Sign Config Screenshot

To Test

Inject test alert. CAP test message text will scroll across LED screen.

Barix Exstreamer (Receiver)

Setup Static IP for Barix device. Use info that was setup in network, include DNS info

Save, Restart and login to new Static IP

Change password and set in Security (Defaults user = admin)

Test and save password in browser

Configuration> Advanced Settings

Stream 1 Reserved for Priority Stream

Stream 2 // (supplied from Instreamer in field)

Stream 3 // (suppplied from OBPlayer at studio)

Audio 80%

No Autoplay or USB

Disable Use SonicIP (don’t want IP spoken over air every reboot)

Instreamer (Encoder)

Setup manual IP for Barix device. Use info that was setup in network, include DNS info

Save, Restart and login to new Static IP

Change password and set in Security

Test and save password in browser

Set IP Streaming info to ICECast

Set IP to send to of the Icecast Server on LS box


Use password ICECast server is expecting to hear.

Use MP3 Codec

Select VBR (CBR Will not work)

Take screenshots of all config pages


OBPlayer ICEcast mountpoint

Create an encoded MP3 stream received by a Barix Exstreamer device hooked to transmitter. This combination creates a robust STL (Studio Transmitter Link)

From Streaming Tab in dashboard create mount point

Enable Streaming Save. Restart.

Mount point will show up in [//localhost:8000]

 BARIX IceCast Screenshot

CAP Alerts with Barix Exstreamer

OBPlayer creates an on demand IceCast mount point when an alert is present with a Barix Exstreamer receiver at transmitter to play CAP alerts. Stations normally will be supplying audio to Exstreamer at transmitter. Barix will be configured to detect and automatically switch to the generated alert mount point the new mount point stream, cut over and play alert, switch back to normal programming when alert stops. .


In order to make the priority streaming work, so that OBPlayer only outputs the alerts and nothing else, disable the scheduler, fallback player, audio in, and the test signal.

Configure OBPlayer

Streaming Tab Create a mount point on local machine’s IceCast server. Exstreamer will switch to the generated alert mount point and switch back when it stops. There is a minor delay in the switching with Barix Exstreamer. Set the lead-in delay to 1 second and the lead-out delay to 5 seconds to catch the whole alert cycle without having too much delay before and after.

Barix>Configuration Set the first URL as priority for the alert stream. Second URL is set to the normal stream coming from the studio.

IceCast Streaming Server

To allow the stream coming from OBPlayer set incoming password in local IceCast server editing config file. This will be the same password that was setup in the dashboard.

sudo nano /etc/icecast2/icecast.xml
    Sources log in with username 'source'
    Relays log in with username 'relay'

    Admin logs in with the username given below

Restart computer for IceCast service to enable saved settings or restart ICECast service from CLI


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