[Discuss-gnuradio] Re: Some questions about audio output and under-runs on a custom block....

[Steve Glass]

Hi,

I've got my custom block producing mono audio at 8KS/s which
I am sending to an audio_sink(8000, "plughw:0,0") and have some
questions.

First question: what is the range of values that each
output sample can assume before clipping? Since they're floats I am
assuming its -1.0 .. +1.0. Is that correct?

Second question: for now I am providing audio silence but get a
constant stream of aU events displayed on the console. I am a little
bothered by that because general_work always produces exactly what its
asked for:

int  
custom_block_ff::general_work(

int nof_output_items, gr_vector_int& nof_input_items, gr_vector_const_void_star& input_items, gr_vector_void_star& output_items)
{
      // handle inputs
      ...

      // produce audio (silence for the time being)
      consume(0, nof_input_items[0]);
      float *out = reinterpret_cast<float*>(output_items[0]);
      fill(out, out + nof_output_items, 0.0);
      return nof_output_items;
}

(and continuing... entering tabs above moved the focus to "send", a space sent the half-complete message. Sigh)

This block consumes its input in a very lumpy manner. A lot of samples are read that produce no output. Then a lot of output is produced at once as the frame is decoded and the output becomes available. That's why I have it producing silence just now... the idea is to smooth the lumpy output and produce whatever output is required even if that is silence.

void
custom_block_ff::forecast(int nof_output_items, gr_vector_int &nof_input_items_reqd)
{
   const size_t nof_inputs = nof_input_items_reqd.size();
   fill(&nof_input_items_reqd[0], &nof_input_items_reqd[nof_inputs], nof_output_items);
}

So, why the audio underruns? Is there a better forecast implementation that will help the scheduler to deal with my "lumpy" output?

Kind regards

Steve

-- 
The highest human happiness is not the exploitation of the present but the preparation of the future.