Re: [Discuss-gnuradio] gr_delay behavior

[Martin Braun]

On Mon, Feb 22, 2010 at 10:42:08AM +0100, Carlos Aviles wrote:
> gr_delay is intended to delay the input of the signal by n samples.
> I've been doing some testing with that block and I have observed that
> the delay is applied to the chunk of data that the block receives as
> input (on my case that was some 8000 samples) and applied again to the
> next chunk.
> 
> I see two problems with that.
> 
> - I'm not able to apply the delay once (to the very beginning of the
> signal). This is actually a very trivial problem that could be solved
> building a custom block.
> - If the delay I want to apply is larger than the size of the data
> that the block receives (say a delay of 10000 samples when the block
> receives the data in chunks of 8000 samples), the signal is set to 0
> as if applying an infinite delay.

If you'd have pasted some code, the diagnosis would have been a bit
simpler, but I'll give it a try:

gr_delay works as you explained. If you set delay to N, the first N-1
outputs will be zero, after that, everything will work as expected.
Of course, you must send at least N items before you get anything at
the output.

Concerning your second point: what do you mean by chunk size? Are you
talking about what GNU Radio passes between blocks? If so, ignore that,
GNU Radio will do the right thing. Or have you set itemsize to 8000 *
gr.sizeof_gr_float? In that case, remember you have to pass 800000000
samples (in blocks of 8000 samples each) through gr_delay before you've
reached a delay of 10000.

Please post your questions such that the answer requires less guesswork.

MB

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