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Re: [Discuss-gnuradio] First time user - fm radio tutorial has choppy au

From: Chris Hallinan
Subject: Re: [Discuss-gnuradio] First time user - fm radio tutorial has choppy audio
Date: Fri, 16 Jan 2015 14:20:57 -0500

On Thu, Jan 15, 2015 at 11:42 PM, Remington Furman <address@hidden> wrote:
Ok, here are the contents of my ~/.gnuradio/config.conf:

default_input_device = default
default_output_device = default
#period_time = 0.010                      # in seconds (default)
period_time = 0.100                      # in seconds
nperiods = 4                 # total buffering = period_time * nperiods
#verbose = false
verbose = true

The actual change I made was to increase audio_alsa/period_time from 0.010 to 0.100.  Play around with it until it works on your system.  My only guess is that perhaps the default ALSA buffer sizes are small enough that they are often consumed by ALSA before GnuRadio will fill them.

Ah ha!
Thanks, Remington.  That was my issue.  My first clue should have been that I was hearing intelligible signal, even though very choppy.  That alone suggest that my flow graph was properly configured with respect to sampling rates, rate conversion (resampling), etc.  Your settings did not work directly on my system (almost stock Ubuntu 14.04) , but improved my situation significantly.  After trying your settings, I got proper sound for about .5 seconds, followed by perhaps a quarter second of dropout.  Playing around, I got smooth audio using these settings:

period_time = 0.400
nperiods = 16

I guess I'm gonna have to learn more about ALSA than I ever wanted to!

Thanks much!



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