[pulseaudio-discuss] [PATCH 2/6] lfe-filter: Enable LFE filter in the resampler
Alexander E. Patrakov
patrakov at gmail.com
Sun Feb 1 07:15:24 PST 2015
29.01.2015 03:14, David Henningsson wrote:
> When enable-lfe-remixing is set, an LFE channel is present in the
> resampler's destination channel map but not in the source channel map,
> we insert a low-pass filter instead of just averaging the channels.
> Other channels will get a high-pass filter.
That's a policy decision. Essentially, your code assumes that the LFE
channel, if present, is correct for the target speakers. Other possible
policies would be to add it to center and then always regenerate it, or
to add the regenerated content to the original LFE content.
But, for the time being, let's proceed with this policy.
>
> In this patch, the crossover frequency is hardcoded to 120Hz (to be fixed
> in later patches).
>
> Note that in current state the LFE filter is
> - not very optimised
> - not rewind friendly (rewinding can cause audible artifacts)
>
> Signed-off-by: David Henningsson <david.henningsson at canonical.com>
> ---
> src/Makefile.am | 3 ++
> src/pulsecore/filter/crossover.c | 79 ++++++++++++++++++++++++++++++-
> src/pulsecore/filter/crossover.h | 6 +++
> src/pulsecore/filter/lfe-filter.c | 97 +++++++++++++++++++++++++++++++++++++++
> src/pulsecore/filter/lfe-filter.h | 38 +++++++++++++++
> src/pulsecore/resampler.c | 34 ++++++++++++--
> src/pulsecore/resampler.h | 3 ++
> 7 files changed, 255 insertions(+), 5 deletions(-)
> create mode 100644 src/pulsecore/filter/lfe-filter.c
> create mode 100644 src/pulsecore/filter/lfe-filter.h
>
> diff --git a/src/Makefile.am b/src/Makefile.am
> index e37a22a..d200271 100644
> --- a/src/Makefile.am
> +++ b/src/Makefile.am
> @@ -911,6 +911,9 @@ lib_LTLIBRARIES += libpulsecore- at PA_MAJORMINOR@.la
>
> # Pure core stuff
> libpulsecore_ at PA_MAJORMINOR@_la_SOURCES = \
> + pulsecore/filter/lfe-filter.c pulsecore/filter/lfe-filter.h \
> + pulsecore/filter/biquad.c pulsecore/filter/biquad.h \
> + pulsecore/filter/crossover.c pulsecore/filter/crossover.h \
> pulsecore/asyncmsgq.c pulsecore/asyncmsgq.h \
> pulsecore/asyncq.c pulsecore/asyncq.h \
> pulsecore/auth-cookie.c pulsecore/auth-cookie.h \
> diff --git a/src/pulsecore/filter/crossover.c b/src/pulsecore/filter/crossover.c
> index 11a8c6e..c902099 100644
> --- a/src/pulsecore/filter/crossover.c
> +++ b/src/pulsecore/filter/crossover.c
> @@ -3,10 +3,10 @@
> * found in the LICENSE file.
> */
>
> -#include "crossover.h"
> #include "biquad.h"
> +#include "crossover.h"
>
> -static void lr4_set(struct lr4 *lr4, enum biquad_type type, float freq)
> +void lr4_set(struct lr4 *lr4, enum biquad_type type, float freq)
> {
> struct biquad q;
> biquad_set(&q, type, freq, 0, 0);
> @@ -23,6 +23,81 @@ static void lr4_set(struct lr4 *lr4, enum biquad_type type, float freq)
> lr4->z2 = 0;
> }
>
> +void lr4_process(struct lr4 *lr4, int samples, int channels, float *data0)
> +{
> + float lx1 = lr4->x1;
> + float lx2 = lr4->x2;
> + float ly1 = lr4->y1;
> + float ly2 = lr4->y2;
> + float lz1 = lr4->z1;
> + float lz2 = lr4->z2;
> + float lb0 = lr4->b0;
> + float lb1 = lr4->b1;
> + float lb2 = lr4->b2;
> + float la1 = lr4->a1;
> + float la2 = lr4->a2;
> +
> + int i;
> + for (i = 0; i < samples; i += channels) {
> + float x, y, z;
> + x = data0[i];
> + y = lb0*x + lb1*lx1 + lb2*lx2 - la1*ly1 - la2*ly2;
> + z = lb0*y + lb1*ly1 + lb2*ly2 - la1*lz1 - la2*lz2;
> + lx2 = lx1;
> + lx1 = x;
> + ly2 = ly1;
> + ly1 = y;
> + lz2 = lz1;
> + lz1 = z;
> + data0[i] = z;
In-place modification. Why?
> + }
> +
> + lr4->x1 = lx1;
> + lr4->x2 = lx2;
> + lr4->y1 = ly1;
> + lr4->y2 = ly2;
> + lr4->z1 = lz1;
> + lr4->z2 = lz2;
> +}
> +
> +void lr4_process_s16(struct lr4 *lr4, int samples, int channels, short *data0)
> +{
> + float lx1 = lr4->x1;
> + float lx2 = lr4->x2;
> + float ly1 = lr4->y1;
> + float ly2 = lr4->y2;
> + float lz1 = lr4->z1;
> + float lz2 = lr4->z2;
> + float lb0 = lr4->b0;
> + float lb1 = lr4->b1;
> + float lb2 = lr4->b2;
> + float la1 = lr4->a1;
> + float la2 = lr4->a2;
> +
> + int i;
> + for (i = 0; i < samples; i += channels) {
> + float x, y, z;
> + x = data0[i];
> + y = lb0*x + lb1*lx1 + lb2*lx2 - la1*ly1 - la2*ly2;
> + z = lb0*y + lb1*ly1 + lb2*ly2 - la1*lz1 - la2*lz2;
> + lx2 = lx1;
> + lx1 = x;
> + ly2 = ly1;
> + ly1 = y;
> + lz2 = lz1;
> + lz1 = z;
> + data0[i] = z;
Filters can overshoot. Please clamp to the range of short.
> + }
> +
> + lr4->x1 = lx1;
> + lr4->x2 = lx2;
> + lr4->y1 = ly1;
> + lr4->y2 = ly2;
> + lr4->z1 = lz1;
> + lr4->z2 = lz2;
> +}
> +
> +
> /* Split input data using two LR4 filters, put the result into the input array
> * and another array.
> *
> diff --git a/src/pulsecore/filter/crossover.h b/src/pulsecore/filter/crossover.h
> index 99a601c..aa1140f 100644
> --- a/src/pulsecore/filter/crossover.h
> +++ b/src/pulsecore/filter/crossover.h
> @@ -25,6 +25,12 @@ struct lr4 {
> float z1, z2;
> };
>
> +void lr4_set(struct lr4 *lr4, enum biquad_type type, float freq);
> +
> +void lr4_process(struct lr4 *lr4, int samples, int channels, float *data0);
> +void lr4_process_s16(struct lr4 *lr4, int samples, int channels, short *data0);
> +
> +
> /* Three bands crossover filter:
> *
> * INPUT --+-- lp0 --+-- lp1 --+---> LOW (0)
> diff --git a/src/pulsecore/filter/lfe-filter.c b/src/pulsecore/filter/lfe-filter.c
> new file mode 100644
> index 0000000..1597eca
> --- /dev/null
> +++ b/src/pulsecore/filter/lfe-filter.c
> @@ -0,0 +1,97 @@
> +/***
> + This file is part of PulseAudio.
> +
> + Copyright 2014 David Henningsson, Canonical Ltd.
> +
> + PulseAudio is free software; you can redistribute it and/or modify
> + it under the terms of the GNU Lesser General Public License as published
> + by the Free Software Foundation; either version 2.1 of the License,
> + or (at your option) any later version.
> +
> + PulseAudio is distributed in the hope that it will be useful, but
> + WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public License
> + along with PulseAudio; if not, write to the Free Software
> + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
> + USA.
> +***/
> +
> +#ifdef HAVE_CONFIG_H
> +#include <config.h>
> +#endif
> +
> +#include "lfe-filter.h"
> +#include <pulse/xmalloc.h>
> +#include <pulsecore/filter/biquad.h>
> +#include <pulsecore/filter/crossover.h>
> +
> +// An LR4 filter, implemented as a chain of two LR2 filters.
As a chain of two Butterworth filters. LR2 is not Butterworth.
Butterworth filter has Q == 0.707, LR2 has Q == 0.5.
> +
> +struct pa_lfe_filter {
> + float crossover;
> + pa_channel_map cm;
> + pa_sample_spec ss;
> + bool active;
> + struct lr4 lr4[PA_CHANNELS_MAX];
The allocation (and the fact that there is one filter per output
channel) is non-obvious here and should be commented better. For each
non-LFE channel, a trivial implementation would have one struct lr4 for
highpass filter and one struct lr4 for lowpass filter. Here you reduced
the number of the needed filters by pre-averaging non-LFE input channels
and running them through a single filter.
> +};
> +
> +pa_lfe_filter_t * pa_lfe_filter_new(const pa_sample_spec* ss, const pa_channel_map* cm, float crossover_freq) {
> +
> + pa_lfe_filter_t *f = pa_xnew0(struct pa_lfe_filter, 1);
> + f->crossover = crossover_freq;
> + f->cm = *cm;
> + f->ss = *ss;
> + pa_lfe_filter_update_rate(f, ss->rate);
> + return f;
> +}
> +
> +void pa_lfe_filter_free(pa_lfe_filter_t *f) {
> + pa_xfree(f);
> +}
> +
> +void pa_lfe_filter_reset(pa_lfe_filter_t *f) {
> + pa_lfe_filter_update_rate(f, f->ss.rate);
> +}
> +
> +pa_memchunk * pa_lfe_filter_process(pa_lfe_filter_t *f, pa_memchunk *buf) {
Maybe a comment is needed that this function expects an average of all
non-LFE channels in the would-be-LFE channel? Not sure how this would
mix with the alternative LFE channel generation policies.
> + int samples = buf->length / pa_sample_size_of_format(f->ss.format);
> +
> + if (!f->active)
> + return buf;
> + if (f->ss.format == PA_SAMPLE_FLOAT32NE) {
> + int i;
> + float *data = pa_memblock_acquire_chunk(buf);
> + for (i = 0; i < f->cm.channels; i++)
> + lr4_process(&f->lr4[i], samples, f->cm.channels, &data[i]);
So, this processes data and puts the result into the same channel. Now I
see why you thought this would be useful.
> + pa_memblock_release(buf->memblock);
> + }
> + else if (f->ss.format == PA_SAMPLE_S16NE) {
> + int i;
> + short *data = pa_memblock_acquire_chunk(buf);
> + for (i = 0; i < f->cm.channels; i++)
> + lr4_process_s16(&f->lr4[i], samples, f->cm.channels, &data[i]);
> + pa_memblock_release(buf->memblock);
> + }
> + else pa_assert_not_reached();
> + return buf;
So, this function always returns buf, and used only as:
buf = pa_lfe_filter_process(r->lfe_filter, buf);
If not PATCH 5/6, I'd tell you to make it void.
> +}
> +
> +void pa_lfe_filter_update_rate(pa_lfe_filter_t *f, uint32_t new_rate) {
> + int i;
> + float biquad_freq = f->crossover / (new_rate / 2);
> +
> + f->ss.rate = new_rate;
> + if (biquad_freq <= 0 || biquad_freq >= 1) {
> + pa_log_warn("Crossover frequency (%f) outside range for sample rate %d", f->crossover, new_rate);
> + f->active = false;
> + return;
> + }
> +
> + for (i = 0; i < f->cm.channels; i++)
> + lr4_set(&f->lr4[i], f->cm.map[i] == PA_CHANNEL_POSITION_LFE ? BQ_LOWPASS : BQ_HIGHPASS, biquad_freq);
> +
> + f->active = true;
> +}
> diff --git a/src/pulsecore/filter/lfe-filter.h b/src/pulsecore/filter/lfe-filter.h
> new file mode 100644
> index 0000000..25db8a0
> --- /dev/null
> +++ b/src/pulsecore/filter/lfe-filter.h
> @@ -0,0 +1,38 @@
> +#ifndef foolfefilterhfoo
> +#define foolfefilterhfoo
> +
> +/***
> + This file is part of PulseAudio.
> +
> + Copyright 2014 David Henningsson, Canonical Ltd.
> +
> + PulseAudio is free software; you can redistribute it and/or modify
> + it under the terms of the GNU Lesser General Public License as published
> + by the Free Software Foundation; either version 2.1 of the License,
> + or (at your option) any later version.
> +
> + PulseAudio is distributed in the hope that it will be useful, but
> + WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public License
> + along with PulseAudio; if not, write to the Free Software
> + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
> + USA.
> +***/
> +
> +#include <pulse/sample.h>
> +#include <pulse/channelmap.h>
> +#include <pulsecore/memchunk.h>
> +
> +
> +typedef struct pa_lfe_filter pa_lfe_filter_t;
> +
> +pa_lfe_filter_t * pa_lfe_filter_new(const pa_sample_spec* ss, const pa_channel_map* cm, float crossover_freq);
> +void pa_lfe_filter_free(pa_lfe_filter_t *);
> +void pa_lfe_filter_reset(pa_lfe_filter_t *);
> +pa_memchunk * pa_lfe_filter_process(pa_lfe_filter_t *filter, pa_memchunk *buf);
> +void pa_lfe_filter_update_rate(pa_lfe_filter_t *, uint32_t new_rate);
> +
> +#endif
> diff --git a/src/pulsecore/resampler.c b/src/pulsecore/resampler.c
> index b4e84f2..34e58e4 100644
> --- a/src/pulsecore/resampler.c
> +++ b/src/pulsecore/resampler.c
> @@ -40,7 +40,7 @@ struct ffmpeg_data { /* data specific to ffmpeg */
>
> static int copy_init(pa_resampler *r);
>
> -static void setup_remap(const pa_resampler *r, pa_remap_t *m);
> +static void setup_remap(const pa_resampler *r, pa_remap_t *m, bool *lfe_filter_required);
> static void free_remap(pa_remap_t *m);
>
> static int (* const init_table[])(pa_resampler *r) = {
> @@ -302,6 +302,7 @@ pa_resampler* pa_resampler_new(
> pa_resample_flags_t flags) {
>
> pa_resampler *r = NULL;
> + bool lfe_filter_required = false;
>
> pa_assert(pool);
> pa_assert(a);
> @@ -390,7 +391,15 @@ pa_resampler* pa_resampler_new(
>
> /* set up the remap structure */
> if (r->map_required)
> - setup_remap(r, &r->remap);
> + setup_remap(r, &r->remap, &lfe_filter_required);
> +
> + if (lfe_filter_required) {
> + pa_sample_spec wss = r->o_ss;
> + wss.format = r->work_format;
> + /* TODO: Temporary code that sets crossover freq to 120 Hz. This should be a parameter */
> + r->lfe_filter = pa_lfe_filter_new(&wss, &r->o_cm, 120.0f);
> + pa_log_debug(" lfe filter activated (LR4 type)");
> + }
>
> /* initialize implementation */
> if (init_table[method](r) < 0)
> @@ -412,6 +421,9 @@ void pa_resampler_free(pa_resampler *r) {
> else
> pa_xfree(r->impl.data);
>
> + if (r->lfe_filter)
> + pa_lfe_filter_free(r->lfe_filter);
> +
> if (r->to_work_format_buf.memblock)
> pa_memblock_unref(r->to_work_format_buf.memblock);
> if (r->remap_buf.memblock)
> @@ -450,6 +462,9 @@ void pa_resampler_set_output_rate(pa_resampler *r, uint32_t rate) {
> r->o_ss.rate = rate;
>
> r->impl.update_rates(r);
> +
> + if (r->lfe_filter)
> + pa_lfe_filter_update_rate(r->lfe_filter, rate);
> }
>
> size_t pa_resampler_request(pa_resampler *r, size_t out_length) {
> @@ -534,6 +549,9 @@ void pa_resampler_reset(pa_resampler *r) {
> if (r->impl.reset)
> r->impl.reset(r);
>
> + if (r->lfe_filter)
> + pa_lfe_filter_reset(r->lfe_filter);
> +
> *r->have_leftover = false;
> }
>
> @@ -731,7 +749,7 @@ static int front_rear_side(pa_channel_position_t p) {
> return ON_OTHER;
> }
>
> -static void setup_remap(const pa_resampler *r, pa_remap_t *m) {
> +static void setup_remap(const pa_resampler *r, pa_remap_t *m, bool *lfe_filter_required) {
> unsigned oc, ic;
> unsigned n_oc, n_ic;
> bool ic_connected[PA_CHANNELS_MAX];
> @@ -740,6 +758,7 @@ static void setup_remap(const pa_resampler *r, pa_remap_t *m) {
>
> pa_assert(r);
> pa_assert(m);
> + pa_assert(lfe_filter_required);
>
> n_oc = r->o_ss.channels;
> n_ic = r->i_ss.channels;
> @@ -752,6 +771,7 @@ static void setup_remap(const pa_resampler *r, pa_remap_t *m) {
> memset(m->map_table_i, 0, sizeof(m->map_table_i));
>
> memset(ic_connected, 0, sizeof(ic_connected));
> + *lfe_filter_required = false;
>
> if (r->flags & PA_RESAMPLER_NO_REMAP) {
> for (oc = 0; oc < PA_MIN(n_ic, n_oc); oc++)
> @@ -863,6 +883,9 @@ static void setup_remap(const pa_resampler *r, pa_remap_t *m) {
>
> oc_connected = true;
> ic_connected[ic] = true;
> +
> + if (a == PA_CHANNEL_POSITION_MONO && on_lfe(b) && !(r->flags & PA_RESAMPLER_NO_LFE))
> + *lfe_filter_required = true;
> }
> else if (b == PA_CHANNEL_POSITION_MONO) {
> m->map_table_f[oc][ic] = 1.0f / (float) n_ic;
> @@ -945,6 +968,8 @@ static void setup_remap(const pa_resampler *r, pa_remap_t *m) {
>
> /* Please note that a channel connected to LFE doesn't
> * really count as connected. */
> +
> + *lfe_filter_required = true;
> }
> }
> }
> @@ -1315,6 +1340,9 @@ void pa_resampler_run(pa_resampler *r, const pa_memchunk *in, pa_memchunk *out)
> buf = remap_channels(r, buf);
> }
>
> + if (r->lfe_filter)
> + buf = pa_lfe_filter_process(r->lfe_filter, buf);
> +
> if (buf->length) {
> buf = convert_from_work_format(r, buf);
> *out = *buf;
> diff --git a/src/pulsecore/resampler.h b/src/pulsecore/resampler.h
> index 0580f85..f60f3b1 100644
> --- a/src/pulsecore/resampler.h
> +++ b/src/pulsecore/resampler.h
> @@ -26,6 +26,7 @@
> #include <pulsecore/memchunk.h>
> #include <pulsecore/sconv.h>
> #include <pulsecore/remap.h>
> +#include <pulsecore/filter/lfe-filter.h>
>
> typedef struct pa_resampler pa_resampler;
> typedef struct pa_resampler_impl pa_resampler_impl;
> @@ -103,6 +104,8 @@ struct pa_resampler {
> pa_remap_t remap;
> bool map_required;
>
> + pa_lfe_filter_t *lfe_filter;
> +
> pa_resampler_impl impl;
> };
>
>
--
Alexander E. Patrakov
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