Advanced Operations

Audio Configurations

There are several ways to inject audio alerts into the broadcast chain. CAP-CP alerts may be issued from the standalone alert player and put into the audio broadcast chain each with their own merits. When an alert is received, audio is sent out for your systems to receive in several ways. Generally there is no audio present unless a message is being issued; either a valid Pelmorex CAP message, Pelmorex test message or when a internal test alert is issued

On Board Audio Out

• Onboard analog stereo 1/8” mini output using Realtek ALC888S codec. Audio present only when a valid CAP message is being broadcast.

• GPIO trigger reverses DTR voltage on pin 4 using RS232 DB9 when CAP message is played to switch an external relay.

• Silence Detection using external third party hardware used to sense audio coming out of the Alert Player and mechanically switch a relay on your board.

• Windows playout machine may use free Silence Detection software from Pira CZ Silence Detector to switch broadcast audio source when CAP message is played.

Reimaging the Player

To restore the original factory configuration, obtain the disk image for your Player from your openbroadcaster.pro user profile.

  1. Use UNETBOOTIN or similar utility to create a bootable USB drive (min. 4Gb) from the disk image.
  2. Insert the USB drive into the OBPlayer, and power up the unit. The imaging process will start auotmatically. A progress bar will display. Be patient at 88% for a few minutes, it really is copying data. Observe activity on USB boot device.

  3. When the process has completed, remove the USB drive and reboot.

Monitoring FM Transmission

An inexpensive FM signal monitoring solution can be acheived using SDR (software defined radio) and a DVB-T USB Tuner based on the Realtek RTL2832U chip. Some clever reverse-engineering exposed the capability of these dongles as FM receivers.

The example below uses a software defined radio (SDR) receiver and a NooElec NESDR Nano RTL2832U receiver.

In order to use the USB DVB-T dongle, you first need to install the rtl-sdr software:

sudo apt-get install rtl-sdr

The dvb_usb_rtl28xxu driver (for enabling TV reception), distributed with newer version of linux, gets loaded by default. Therefore, the driver must be unloaded for SDR to work, each time the dongle is inserted.

sudo rmmod dvb_usb_rtl_28xxu

To prevent the default dvb_usb driver from being loaded on reboot, it can be blacklisted. Create the file (use sudo) in /etc/modprobe.d/blacklist-rtl.conf, add the following line :

blacklist dvb_usb_rtl28xxu

Now you can check if your USB device can be detected. Insert the USB dongle, and use the rtl command line utilities:

rtl_test -t

The FM reception may be streamed over TCP to allow remote monitoring of the broadcast signal, using the rtl_tcp utility, where host_ip is the IP address of the host:

rtl_tcp -a host_ip 

For example rtl_tcp -a 10.0.0.106

You should now be able to use SDR to remotely monitor the stream over the network, using gqrx for example.

sudo apt-get install gqrx-sdr

Launch the program with the command:

gqrx

The first window to appear is for configuring the input source and audio output. Set the Device option to ‘Other’ and type ‘rtl_tcp=host_ip:1234’ into the Device String (host_ip is the IP address used in the previous step).

Activate gqrx by clicking on the grey start/stop button just below the File menu. Noise should be heard from your speaker or head-phones, if not, check your audio volume control.

To tune the received frequency move the mouse pointer on any of the frequency digits and use the mouse wheel to change it. Alternatively you can move the pointer and click on the upper or lower part of any digit or use the Up/Down key to change it.

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