29 Oct
2006
29 Oct
'06
7:55 p.m.
Hello all,
Core Sound <http://www.core-sound.com/default.php> willsoon
be offering a tetrahedral (Ambisonic) microphone at a very
reasonable price. They are also working on a combined preamp
+ AD converter unit for this mic. This will be able to multiplex
the 4 channels over a single SPDIF link, by using it a the
double sample frequency.
I'm currently working on a software controller unit for this
microphone. It will perform A-format to B-format conversion,
and allow measured impulse responses to be used for calibrating
the four mics. The result should be a very high quality portable
surround recording system at a reasonable price (compared to other
solutions which cost easily five times as much).
The remaining problem is the demultiplexing of the two double
speed SPDIF channels to four channels. It could either be done
within the ALSA layer, or in JACK's ALSA backend. Doing this
in a JACK client will not work unless it would be the only
client - all others would get the wrong idea of the sample
frequency and buffer size.
So here's my question to both the ALSA and JACK teams: what
would be your idea of a solution for this ?
--
FA
Lascia la spina, cogli la rosa.
30 Oct
30 Oct
7:40 a.m.
New subject: [linux-audio-dev] Re: [Jackit-devel] Multiplexing 4 channels on SPDIF
Fons Adriaensen wrote:
Core Sound
<http://www.core-sound.com/default.php> willsoon
be offering a tetrahedral (Ambisonic) microphone at a very
reasonable price. They are also working on a combined preamp
+ AD converter unit for this mic. This will be able to multiplex
Sounds nice :)
So here's my question to both the ALSA and JACK
teams: what
would be your idea of a solution for this ?
Some ALSA plugin? Of course, doing it in JACK's ALSA backend is also
reasonably simple, but would require small changes in many places to
override samplerates, etc.
- Jussi
11:06 a.m.
New subject: [linux-audio-dev] Re: [Jackit-devel] Multiplexing 4 channels on SPDIF
On Mon, 2006-10-30 at 13:40 +0200, Jussi Laako wrote:
Fons Adriaensen wrote:
I don't think it even needs to be a plugin, just tell ALSA about the
audio format. Where can the detailed specs be downloaded?
Lee
Core Sound
<http://www.core-sound.com/default.php> willsoon
be offering a tetrahedral (Ambisonic) microphone at a very
reasonable price. They are also working on a combined preamp
+ AD converter unit for this mic. This will be able to multiplex
Sounds nice :)
So here's my question to both the ALSA and
JACK teams: what
would be your idea of a solution for this ?
Some ALSA plugin? Of course, doing it in JACK's ALSA backend is also
reasonably simple, but would require small changes in many places to
override samplerates, etc. 
12:36 p.m.
New subject: [linux-audio-dev] Re: [Jackit-devel] Multiplexing 4 channels on SPDIF
On Mon, Oct 30, 2006 at 10:07:06AM -0500, Lee Revell wrote:
How can you tell ALSA that an SPDIF input is 4 channels ?
Some ALSA
plugin? Of course, doing it in JACK's ALSA backend is also
reasonably simple, but would require small changes in many places to
override samplerates, etc.
I don't think it even needs to be a plugin, just tell ALSA about the
audio format. Where can the detailed specs be downloaded?
According to the Core Sound website this thing is still in development,
and the specs there are incomplete.
What they want to do is trick hardware 2-ch recorders into accepting
the 4-ch signal. So what is in reality 4 channels at 48 kHz will be
presented as 2 channels at 96 kHz.
--
FA
Lascia la spina, cogli la rosa.
12:41 p.m.
New subject: [Jackit-devel] [linux-audio-dev] Re: Multiplexing 4 channels on SPDIF
On Mon, 2006-10-30 at 17:35 +0100, Alfons Adriaensen wrote:
I don't think it's useful to discuss further until technical details are
available.
When specs are available, this thread should probably be re-started on
alsa-devel.
Lee
On Mon, Oct 30, 2006 at 10:07:06AM -0500, Lee Revell
wrote:
How can you tell ALSA that an SPDIF input is 4 channels ?
The ALSA code would have to be extended... I'm not sure exactly where.
I don't think it should be called SPDIF because SPDIF implies two
channels.
Some ALSA
plugin? Of course, doing it in JACK's ALSA backend is also
reasonably simple, but would require small changes in many places to
override samplerates, etc.
I don't think it even needs to be a plugin, just tell ALSA about the
audio format. Where can the
detailed specs be downloaded?
According to the Core Sound website this thing is still in development,
and the specs there are incomplete.
What they want to do is trick hardware 2-ch recorders into accepting
the 4-ch signal. So what is in reality 4 channels at 48 kHz will be
presented as 2 channels at 96 kHz.
1:50 p.m.
New subject: [Jackit-devel] [linux-audio-dev] Re: Multiplexing 4 channels on SPDIF
On Mon, Oct 30, 2006 at 11:41:36AM -0500, Lee Revell wrote:
On Mon, 2006-10-30 at 17:35 +0100, Alfons Adriaensen
wrote:
What do you need more than what is available on http://www.core-sound.com/4Mic/2.php ?
It doesn't say how the multiplexing is done, but that's probably easy enough to
find out and is not the real problem. Probably it's just alternating channels,
but I will ask them. Everything else is there AFAICS.
The real question is how to fit this into the existing architecture:
- hardware presents itself as 2 * 96 kHz
- user wants to see a device with 4 * 48 kHz.
Is there any online documentation on how to write ALSA plugins ?
--
FA
Lascia la spina, cogli la rosa.
What they want to do is trick hardware 2-ch
recorders into accepting
the 4-ch signal. So what is in reality 4 channels at 48 kHz will be
presented as 2 channels at 96 kHz.
I don't think it's useful to discuss further until technical details are
available.
2:30 p.m.
New subject: [Jackit-devel] [linux-audio-dev] Re: Multiplexing 4 channels on SPDIF
On Mon, 2006-10-30 at 18:52 +0100, Fons Adriaensen wrote:
The real question is how to fit this into the existing
architecture:
- hardware presents itself as 2 * 96 kHz
- user wants to see a device with 4 * 48 kHz.
Is there any online documentation on how to write ALSA
plugins ?
No, ask on the ALSA list.
Lee
4 Nov
4 Nov
6:06 p.m.
New subject: [Jackit-devel] [linux-audio-dev] Re: Multiplexing 4 channels on SPDIF
On Mon, Oct 30, 2006 at 01:30:53PM -0500, Lee Revell wrote:
On Mon, 2006-10-30 at 18:52 +0100, Fons Adriaensen
wrote:
Joined the alsa-devel list and asked if such a thing would be possible.
Five days later: more spam than I've had in a year and no reply.
Today I wrote a JACK backend that does the job.
--
FA
Lascia la spina, cogli la rosa.
The real question is how to fit this into the
existing architecture:
- hardware presents itself as 2 * 96 kHz
- user wants to see a device with 4 * 48 kHz.
Is there any online documentation on how to write
ALSA plugins ?
No, ask on the ALSA list. 
30 Oct
30 Oct
3:56 p.m.
New subject: [Jackit-devel] [linux-audio-dev] Re: Multiplexing 4 channels on SPDIF
On Mon, 2006-10-30 at 18:52 +0100, Fons Adriaensen wrote:
- hardware presents itself as 2 * 96 kHz
- user wants to see a device with 4 * 48 kHz.
interestingly, ADAT devices do the opposite to get to SR's above 48kHZ:
- hardware runs as N * 48 kHz channels
- data is multiplexed across 2 channels at once
- user sees N/2 channels at 96kHz
this is not done with ALSA plugins, but in the driver.
note that JACK wants if possible to sit close to the h/w, so an ALSA
plugin is not ideal. JACK uses mmap to read/write data from/to the
device, so the work of an ALSA plugin is hard ...
--p
4:24 p.m.
New subject: [Jackit-devel] [linux-audio-dev] Re: Multiplexing 4 channels on SPDIF
On Mon, Oct 30, 2006 at 02:55:33PM -0500, Paul Davis wrote:
On Mon, 2006-10-30 at 18:52 +0100, Fons Adriaensen
wrote:
Yes, there should be as little as possible between JACK and the
hardware. But providing a memory mapped interface should not be
too difficult. Maybe it's even easier than any other one - all
the plugin needs to do is provide a pointer to its own buffers
using ALSA's mmapped API.
BTW, it has for long been my opinion that there is no need for
ALSA to provide anything else than the mmapped interface.
The other solution (which I would not dislike) is to do the
demuxing in JACK's backend.
--
FA
Lascia la spina, cogli la rosa.
- hardware presents itself as 2 * 96 kHz
- user wants to see a device with 4 * 48 kHz.
interestingly, ADAT devices do the opposite to get to SR's above 48kHZ:
- hardware runs as N * 48 kHz channels
- data is multiplexed across 2 channels at once
- user sees N/2 channels at 96kHz
this is not done with ALSA plugins, but in the driver.
note that JACK wants if possible to sit close to the h/w, so an ALSA
plugin is not ideal. JACK uses mmap to read/write data from/to the
device, so the work of an ALSA plugin is hard ...
6622
days inactive
6628
days old
linux-audio-dev@lists.linuxaudio.org
9 comments
5 participants
participants (5)
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Alfons Adriaensen -
Fons Adriaensen -
Jussi Laako -
Lee Revell -
Paul Davis