I have a GNU Radio Companion flow graph, where I have the following connections:

  • 440Hz cosine wave
  • throttle block
  • audio sink

Flow Graph Screenshot

All of the above blocks use the same sample rate (48KHz).

When I execute this flow graph, I don't get a continuous note, the way I expected. Instead, it pulses on and off, several times per second. Why is this?

How can I make it output a continuous 440Hz tone?

Removing the Throttle block makes it stop cutting in and out, but it sounds even worse when I do this.

I have tried this setup, with and without the Throttle block, at all common sample rates for sound cards.


1 Answer 1


I ended up figuring it out. I had to do three things:

  • remove the Throttle block
  • enable the "OK to Block" option in the audio sink
  • ensure the amplitude of the sine wave is less than 1
  • $\begingroup$ indeed; GNU Radio Companion will even tell you about not using hardware blocks with a Throttle block in the same flow graph $\endgroup$ Jun 16, 2019 at 10:26

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