[pulseaudio-discuss] [RFC PATCH 0/6] LFE filter

[David Henningsson]

Hi!

Hui and I have been working on some LFE filter patches lately, and this
is our first draft for review/feedback.

First, I have greedily stolen the math from CRAS, because CRAS is BSD and
as I understand we don't have a problem with merging more liberal licenses.

The LFE filter is implemented in the resampler, which means it is done for
every sink-input rather than every sink - this might mean some additional
CPU processing if many different streams play back at the same time, but
putting it on the sink side would disable the possibility to mix a 2.0 stream
with a 2.1 stream.

The rewind part is very drafty and untested, and I'm not sure I choose the
best design here. But at least this is something that could act as base for
discussion.

Also, while testing we noticed that flat volumes acts a bit weird, making it
impossible to have a high subwoofer volume level but at the same time low
front speaker volume, but I'm not sure if that's a bug or just the (ahem)
normal weirdness of flat volumes.

David Henningsson (4):
  lfe-filter: Import code from the Chrome OS audio server
  lfe-filter: Enable LFE filter in the resampler
  lfe-filter: Add rewind support
  resampler: Make some basic functions for rewinding

Hui Wang (2):
  daemon-conf: enable the lfe remixing by default
  lfe-filter: change the crossover frequency as a parameter

 LICENSE                                    |   3 +
 man/pulse-daemon.conf.5.xml.in             |   7 +-
 src/Makefile.am                            |   3 +
 src/daemon/daemon-conf.c                   |   5 +-
 src/daemon/daemon-conf.h                   |   1 +
 src/daemon/daemon.conf.in                  |   3 +-
 src/daemon/main.c                          |   1 +
 src/modules/module-virtual-surround-sink.c |   2 +-
 src/pulsecore/core.c                       |   1 +
 src/pulsecore/core.h                       |   1 +
 src/pulsecore/filter/LICENSE.WEBKIT        |  27 +++
 src/pulsecore/filter/biquad.c              | 368 +++++++++++++++++++++++++++++
 src/pulsecore/filter/biquad.h              |  57 +++++
 src/pulsecore/filter/crossover.c           | 263 +++++++++++++++++++++
 src/pulsecore/filter/crossover.h           |  76 ++++++
 src/pulsecore/filter/lfe-filter.c          | 187 +++++++++++++++
 src/pulsecore/filter/lfe-filter.h          |  39 +++
 src/pulsecore/resampler.c                  |  49 +++-
 src/pulsecore/resampler.h                  |   7 +
 src/pulsecore/sink-input.c                 |   6 +-
 src/pulsecore/source-output.c              |   4 +-
 src/tests/remix-test.c                     |   3 +-
 src/tests/resampler-test.c                 |   7 +-
 23 files changed, 1106 insertions(+), 14 deletions(-)
 create mode 100644 src/pulsecore/filter/LICENSE.WEBKIT
 create mode 100644 src/pulsecore/filter/biquad.c
 create mode 100644 src/pulsecore/filter/biquad.h
 create mode 100644 src/pulsecore/filter/crossover.c
 create mode 100644 src/pulsecore/filter/crossover.h
 create mode 100644 src/pulsecore/filter/lfe-filter.c
 create mode 100644 src/pulsecore/filter/lfe-filter.h

-- 
1.9.1