[pulseaudio-discuss] New Module: module-lfe-lp

Tanu Kaskinen tanuk at iki.fi
Thu Mar 21 00:38:05 PDT 2013

On Wed, 2013-03-20 at 17:50 +0600, Alexander E. Patrakov wrote:
> 2013/3/20 Matthew Robbetts <wingfeathera at gmail.com>:
> > Ah sorry, I see what you mean. Yes, you're right.
> (except for the typo: 2 -> sqrt(2))
> > Either, the
> > coefficient design code should be changed to the arbitrary filtering
> > correctly (probably quite a lot more code to do this), or the the user
> > interface should be constrained to only actually allow the user to ask
> > for second-order Butterworth. I agree that the latter is probably more
> > suitable.
> >
> > I clearly have not added very much here. Sorry for the noise!
> No need to say sorry. We do need your eyes for the next round of DSP reviews.
> Tanu: I am still waiting for your reply regarding the best way to do
> clickless rewinds in IIR filters (i.e. one of: "disallow rewinds",
> "keep full history of the intermediate state", or some creative
> solution).

Oh, I didn't realize that a reply was needed. Your description of the
problem and the suggested solutions were pretty spot on.

Keeping a full history of the internal state would be the best solution,
as far as I can see. "Full" means
pa_memblockq_get_maxrewind(u->memblockq). Changes to the maxrewind value
can be caught in sink_input_update_max_rewind_cb().

Disallowing rewinds would probably be easier to implement, but it can
cause unacceptable latency for volume changes etc.


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