Re: [Discuss-gnuradio] filter taps and delays

[Tom Rondeau]

On Sun, Jan 5, 2014 at 4:39 PM, Miklos Maroti <address@hidden> wrote:
> Hi Guys,
>
> If I use interp_fir_filter_ccc(3, [1, 2, 3, 4, 5, 6]) on a vector
> source containing [1, 0, 0, ...] then I get [1, 2, 3, 4, 5, 6, 0, 0,
> ...] as expected. However, if I use interp_fir_filter_ccc(3, [1, 2, 3,
> 4, 5]) then I get [0, 1, 2, 3, 4, 5, 0, 0, ...] so the samples are
> shifted to the right by one. For taps of length divisible by 3 there
> is no delay, and for others there is 1 or 2 sample delay introduced by
> the interpolation filter. Why is this?

Good catch, Miklos. I've identified the problem. I've put it into a
queue of patches that will be pushed soon.

> Also, maybe related to this, I see filter.declare_sample_delay(0) in
> generated code, and I do not know what it does and if it is strictly
> necessary.
>
> Miklos

No, that has nothing to do with it. That is a very specialized
function to instruct the scheduler how to handle tags when passing
through blocks with delay. The documentation of that function tells
you that it doesn't do anything with the signal processing of the
block:

http://gnuradio.org/doc/doxygen/classgr_1_1block.html#acad5d6e62ea885cb77d19f72451581c2

Tom