06.11.2014 15:39, David Henningsson wrote:
On 2014-09-30 15:59, Alexander E. Patrakov wrote:
30.09.2014 19:07, David Henningsson wrote:
On 2014-09-26 14:17, Tanu Kaskinen wrote:
A summary of my proposal:
To add LFE low-pass filtering, just hack the current remixer
implementation, no need for interface changes anywhere.
Actually, I think this could be good enough, at least as a first step.
Do you think it would be okay to:
- Implement a LR2 or LR4 filter by "hacking the current remixer
implementation"
For me, it would be okay, but I would prefer a slightly more complex
plan, purely to avoid the blame of the form "you demand fully rewindable
code everywhere from others but just wrote an LFE-remixer that doesn't
handle rewinds correctly". The plan is:
1. Implement functions to calculate the coefficients of the required IIR
filters for LR2 and/or LR4.
2. Implement, in a separate file, some set of functions that would allow
one to apply an arbitrary matrix of IIR filters on a memblockq. Make
sure they are fully rewindable (that's the PR part), write a test.
3. Connect functions from (2) to the existing remixer implementation. If
it turns out that it is impossible to form the rewind requests
correctly, write a TODO item.
(2), except the test, already sits on my laptop since the previous year
in the form of a virtual sink. I just need to refactor it from the
"parallel biquads" to the "chain of biquads" form (because both LR2 and
LR4 have pairs of identical poles which are inexpressible in the
parallel-biquads formulation) and remove the sink code.
Reviving this thread due to renewed interest from management. In short,
we should probably go ahead and write this filter. I can certainly try
to do it, but I assume you will just complain about me breaking the
math. :-)
That's OK.
Did you end up doing anything more with your existing code? Need a hand
anywhere?
No. In fact, I have not looked at PulseAudio code (except Peter's
patches) since the conference, and I don't have enough free time. The
earliest date when I can continue is this Sunday.
--
Alexander E. Patrakov
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