[gstreamer-bugs] [Bug 567577] [audiofx] Add generic IIR/FIR audio filter elements

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-good | Ver: HEAD CVS




------- Comment #3 from Sebastian Dröge  2009-01-13 12:48 UTC -------
(In reply to comment #2)
> Looks good, some questions:
> 
> 1) Would it be easy to add one sample of how to use the kiss-ftt to calculate
> the kernel?

No, that'll be easy. I'll also add a sample for every element on how to use it
from C.

> 2) in The doc-blob for 'element-audiofirfilter':
>   2a) what is the relation of the configured latency and the number of
> coefficients in the kernel (is there any). Or are there some guidelines for
> setting a good latency. I mean just setting this to 0 would most probably not
> work, but then nobody wants latency.

The latency depends on the filter kernel. It could be from 0 to
kernel_length-1. For example if you have a kernel [0, 0, 1] the latency
introduced by the kernel would be 2 (the output of the filter would be the
input of the filter shifted by two samples).

>   2b) just link the first occurance of FIR to the wikipedia article and drop
> the later link (same for iir).

Good point :)

> 3) GstAudioFIRFilter::rate-changed: Why is the signal needed. What about
> notify::caps for the src or sink pad? Also isn't the signal dangerous, what
> about a bus message.

I used this signal instead of notify::caps because a user of the filter
probably doesn't want to know about gstreamer internals like caps and only
cares about the sampling rate. Also this could be improved a bit to be only
emitted if the sampling rate changes (and not always when the caps are
changing).

A bus message won't work because you usually don't want to start processing
buffers until the signal is completely handled (and a new filter kernel /
coefficients are calculated and set for the new sampling rate).


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