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-Broadcast.

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 GPIO Trigger Switching Relay

GPIO Trigger with RS-232 DTR on CAP-CP Alerts. When enabled and a matching CAP message is broadcast, an alert cycle starts, the serial port will be opened and the DTR line will be set. After the alert cycle has completed, the DTR line will be cleared and a relay will be closed. 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).

“Lead-In Delay (in seconds)”. This is the number of seconds of silence that will be inserted at the beginning of each alert cycle before the first alert starts playing, but after the DTR/icecast stream notifies that an alert cycle has started. The default is 1 second. Always leave it at 1 or greater. Setting this to 5 or so seconds will give time for buffering to occur.

“Trigger RS-232 DTR on Alerts” checkbox, when checked, will show the “RS-232 Device Filename” option. The device filename should be something like /dev/ttyS0, or /dev/ttyUSB0 if using a USB-to-Serial adapter. For initial setup, disable all RS-232 ports so there is only one available.

The “Trigger Icecast Stream on Alerts” setting will start and stop the icecast streamer module (in the streaming tab) the same as the serial port. In addition to this setting, you must also uncheck the “Play Stream on Startup” option on the streaming tab, or else the streamer will start playing when obplayer starts.

 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 Enable Trigger RS-232 DTR on Alert signal RS-232 Device should be set to serial port (/dev/ttyS0 for Port 1, /dev/ttyS1 for Port 2).


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)

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


Find a OBPlayer or OBServer Bug? Have a OBPlayer or OBServer feature request ?
We really appreciate your feedback!

Open Server Bugs

Open Player Bugs