30 Aug
2010
30 Aug
'10
2 p.m.
Hi,
I want to make is a DSP module that improves the sound quality
of the sound coming from the laptop builtin speakers by applying DSP
(FIR/IIR filters).
I want to route all audio played back (from for
instance an offline WAV or MP3 file, from a movie, or streamed from the internet) to
pass through the
DSP plugin whenever headphones are NOT connected. When headphones are connected no
processing should be applied.
I
want to place the DSP module as close to the hardware as possible to
make sure all audio is really routed through the DSP plugin so I always
can enjoy
the DSP improvements made to the sound.
Where should I place this module/DSP code?
- As a plugin to PulseAudio?
- As a plugin to ALSA?
- As its own virtual sound card?
- In the audio driver for my built-in sound card?
- As a kernel module?
I have tried loading the LADSPA-module using the module-ladspa-sink in PulseAudio but I am
not sure this is the best solution.
I need to remove some limitations in module-ladspa-sink to get it working properly (
multichannel audio, only DSP processing for internal speakers).
My requirements:
1) Must be able to detect if headphones are connected
2) Must be able to process stereo and multichannel (5.1/7.1) formats. I
need the multichannel formats to perform binaural downmixing to
stereo.
So it is important that I can receive multichannel audio and mix it down to stereo and
output it to a stereo soundcard.
/Kim
30 Aug
30 Aug
2:18 p.m.
On Mon, August 30, 2010 5:00 am, Kim Therkelsen wrote:
Hi,
I want to make is a DSP module that improves the sound quality
of the sound coming from the laptop builtin speakers by applying DSP
(FIR/IIR filters).
I want to route all audio played back (from for
instance an offline WAV or MP3 file, from a movie, or streamed from the
internet) to
pass through the
DSP plugin whenever headphones are NOT connected. When headphones are
connected no processing should be applied.
I
want to place the DSP module as close to the hardware as possible to
make sure all audio is really routed through the DSP plugin so I always
can enjoy
the DSP improvements made to the sound.
Where should I place this module/DSP code?
- As a plugin to PulseAudio?
- As a plugin to ALSA?
- As its own virtual sound card?
- In the audio driver for my built-in sound card?
- As a kernel module?
I have tried loading the LADSPA-module using the module-ladspa-sink in
PulseAudio but I am not sure this is the best solution.
It is the recommended solution if you are using PA for your sound server.
I need to remove some limitations in
module-ladspa-sink to get it working
properly ( multichannel audio, only DSP processing for internal speakers).
My requirements:
1) Must be able to detect if headphones are connected
IIUC, PA gets this info from ALSA
2) Must be able to process stereo and multichannel
(5.1/7.1) formats. I
need the multichannel formats to perform binaural downmixing to
stereo.
I'm not sure how the dolby multichannel support is in ALSA. It may depend
on the internal capabilities of the device.
So it is important that I can receive multichannel
audio and mix it down
to stereo and output it to a stereo soundcard.
This may better handled in app.
--
Patrick Shirkey
Boost Hardware Ltd.
2:48 p.m.
I have tried
loading the LADSPA-module using the module-ladspa-sink in
PulseAudio but I am not sure this is the best solution.
It is the recommended solution if you are using PA for your sound server. 2) Must be
able to process stereo and multichannel (5.1/7.1) formats. I
need the multichannel formats to perform binaural downmixing to
stereo.
I'm not sure how the dolby multichannel support is in ALSA. It may depend
on the internal capabilities of the device.
So it is important that I can receive
multichannel audio and mix it down
to stereo and output it to a stereo soundcard.
This may better handled in app.
3:08 p.m.
On Mon, August 30, 2010 5:48 am, Kim Therkelsen wrote:
Why is it better than loading it using the ALSA LADSPA plugin loader
module?
To me it seems better to load it into ALSA because it does not depend on
whether PulseAudio is used or not.
If it should be used in different Linux based operating systems I can not
always rely on PulseAudio being present.
The idea is that I perform the same processing no matter what user
application is used to playback the audio/video.
The plugin must receive the raw six (or eight) channel audio PCM stream.
So I do not want to make the DSP processing specific to some special
application only.
It's a noble goal but as you are attempting to cater to such a varied
range of systems that it is hard to recommend a perfect solution. You
should really isolate the core requirements and minimum apps that it will
work with then it will be easier for people to make a suggestion that fits
your needs.
--
Patrick Shirkey
Boost Hardware Ltd.
I have
tried loading the LADSPA-module using the module-ladspa-sink in
PulseAudio but I am not sure this is the best solution.
It is the recommended solution if you are using PA for your sound
server. 2) Must
be able to process stereo and multichannel (5.1/7.1) formats.
I
need the multichannel formats to perform binaural
downmixing to
stereo.
I'm not sure how the dolby multichannel support is in ALSA. It may
depend
on the internal capabilities of the device.
So it is important that I can receive
multichannel audio and mix it
down
to stereo and output it to a stereo soundcard.
This may better handled in app.
3:45 p.m.
The idea is
that I perform the same processing no matter what user
application is used to playback the audio/video.
The plugin must receive the raw six (or eight) channel audio PCM stream.
So I do not want to make the DSP processing specific to some special
application only.
It's a noble goal but as you are attempting to cater to such a varied
range of systems that it is hard to recommend a perfect solution. You
should really isolate the core requirements and minimum apps that it will
work with then it will be easier for people to make a suggestion that fits
your needs. 
4:11 p.m.
On Mon, 30 Aug 2010, Kim Therkelsen wrote:
>> The idea is that I perform the same processing no matter what user
>> application is used to playback the audio/video.
>> The plugin must receive the raw six (or eight) channel audio PCM stream.
>> So I do not want to make the DSP processing specific to some special
>> application only.
[snip]
I want to use the solution in Meego, Android, and Google
Chrome OS - if possible. I do not know what applications
MeeGo: pulseaudio or ALSA
Google: pulseaudio or ALSA (AFAIK)
With Android, Linux is just a prop to get the JVM started...
so your solution will probably need to be in Java there.
All the operating systems are based on Linux so they
must
have something in common regarding the audio chain (such
as ALSA) where I can plug our DSP code in.
PulseAudio: if you implement it here, you will probably get
the most bang for your buck... and it is more likely to
integrate well into the end-user's system. However,
PulseAudio is not a "universal" solution for Linux. (For
example, Pro Audio users will often uninstall PulseAudio
from their systems.)
ALSA: ALSA /is/ universal to Linux and is definately capable
of doing this task. You'll probably want to implement it as
an ALSA plug-in. However, the end-user experience is
usually not as slick and (IMHO) the ALSA API is a fickle
friend. Also, more times than not I hear people say, "DON'T
use the ______ ALSA plug-in. It's totally broken. Instead
use [SOME USER APPLICATION ALTERNATIVE]."
-gabriel
4:44 p.m.
On Mon, Aug 30, 2010 at 9:45 AM, Kim Therkelsen <kim_t26(a)hotmail.com> wrote:
Yes , I understand, there probably is no simple
answer.
I normally make applications for Microsoft Windows and don't know much about
Linux.
If you make a virtual sound card in Windows you have a solution that covers
all applications.
I assume it must be possible to do something similar in Linux.
No, this isn't true. Virtual sound cards in Windows don't cover all
applications. Linux also has such "virtual sound cards" (via a variety
of different mechanisms) but just as the most common way to implement
a virtual sound card on Windows won't address apps like Sonar or
Reason (or it certainly won't address their issues), the "virtual
sound cards" on Linux will work well for some applications and not for
others.
I want to use the solution in Meego, Android, and
Google Chrome OS - if
possible.
it would have been useful for you to have described this up front -
you're clearly operating in a very different application niche than
most (not all) of the developers on this list. for most of us, mobile
device targetting is not particularly central, and the technologies
that we generally use to get audio in and out of the computer are
pretty different than the ones that would be used on your system.
most/many of us here are pretty firmly rooted on the desktop, in
environments where low latency is important and the i/o devices are
often *not* built into the system (and in some cases, may not even be
accessible via ALSA).
i'm afraid i don't have anything to offer for solutions in this kind
of environment, but perhaps someone else will.
4987
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4987
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linux-audio-dev@lists.linuxaudio.org
6 comments
4 participants
participants (4)
-
Gabriel M. Beddingfield -
Kim Therkelsen -
Patrick Shirkey -
Paul Davis