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For many communications systems, latency and turn around time may be a concern.  The following test setup was used to measure the end to end latency of an USRP based receiver against a conventional analog receiver.  The USRP and analog receiver were configured to demodulate a NB-FM (Narrow Band FM) audio signal.  The test transmitter was keyed and then one of its DTMF (touch tone) buttons was pushed to generate an audio signal.  The stereo input of a stand alone system were used to capture the audio streams from both devices.  Using a standard audio capture program, it was possible to measure the delay between the channels.

Test Setup

The following chart shows an end to end delay of 48mS.  The audio board sample rate was set to 192KHz and the time scale at the top of the application is set to display samples.  Note the latency of this system includes the USB 2.0 interface, GNU radio processing and filters, and ALSA sound driver.

GNU Radio System Latency.


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