14 Apr
2004
14 Apr
'04
4:34 p.m.
On Apr 14, 2004, Anders Torger wrote:
Thus, I think it is necessary to implement something
operating on the
ethernet level to get best performance in terms of throughput and
latency.
/Anders Torger
If what you mean by "operating at the ethernet level" means
"no Cobra-like hardware to help, but putting data directly
into Etherframes w/o IP/RTP headers", then its unclear to me that
working at the RTP/IP level is going to hurt you much. The
simplest implementation would have RTP/IP header overhead,
but there are nice header compression schemes that get rid of it:
http://www.ietf.org/rfc/rfc2508.txt
and its improved versions. By using RTP, you get a lot of
protocol design you might otherwise need to do,
within RTP (like RTP MIDI) and surrounding it
(session management, etc).
One big thing you need to worry about are clocks -- unlike
a protocol like AES/EBU or SPIDF, packet-based media is
not sending an implicit clock along with the data. So, the
nominal "sender sampling rate" can't be precisely linked to
the nominal "receiver sampling rate" in a simple way. The
consequence is either too much data piles up at the receiver,
or not enough. One solution to this problem is to continuously
running a sample-rate converter at the receiver in software,
to keep the two sampling rates locked. See:
http://www1.ietf.org/mail-archive/working-groups/avt/current/
msg00569.html
and use the "Thead Next" to cycle through the discussion, it
goes on a ways and lots of interesting folks drop in with info.
A separate issue for your "many streams" case is synchronizing
the streams to each other, in the case where not all share the
same nominal clock. RTP has tools for this, based on
associating NTP timestamps from a common clock to each
independent stream, that get used for audio/video lipsync,
and can be repurposed here as well.
---
John Lazzaro
http://www.cs.berkeley.edu/~lazzaro
lazzaro [at] cs [dot] berkeley [dot] edu
---
15 Apr
15 Apr
6:13 a.m.
On Wednesday 14 April 2004 22.27, John Lazzaro wrote:
If what you mean by "operating at the ethernet
level" means
"no Cobra-like hardware to help, but putting data directly
into Etherframes w/o IP/RTP headers", then its unclear to me that
working at the RTP/IP level is going to hurt you much. The
simplest implementation would have RTP/IP header overhead,
but there are nice header compression schemes that get rid of it:
http://www.ietf.org/rfc/rfc2508.txt
and its improved versions. By using RTP, you get a lot of
protocol design you might otherwise need to do,
within RTP (like RTP MIDI) and surrounding it
(session management, etc).
Perhaps RTP is good enough. However, at several hundreds of megabits of
throughput, it could be valuable not needing to calculate checksums in
software. I guess IP and UDP checksums usually are calculated in
software. Possibly other CPU time/latency inducing layers can be
bypassed by accessing the ethernet layer directly, and possibly the use
of jumbo frames etc is better controlled then.
RTP is not designed for the same purpose though, it would be a bit
overkill. Using RTP would give the impression that the solution would
work over a large routed network, although it will only work in a tight
isolated ethernet running no traffic but audio.
One big thing you need to worry about are clocks --
unlike
a protocol like AES/EBU or SPIDF, packet-based media is
not sending an implicit clock along with the data. So, the
nominal "sender sampling rate" can't be precisely linked to
the nominal "receiver sampling rate" in a simple way. The
consequence is either too much data piles up at the receiver,
or not enough. One solution to this problem is to continuously
running a sample-rate converter at the receiver in software,
to keep the two sampling rates locked. See:
The sample clock is passed separately with for example wordclock. I
don't expect to use more than one computer with a sound card in most
cases though, so then it is a non-issue.
The idea is basically take inputs on the sound card, broadcast them to
the convolver nodes, which convolves and unicast back the result to the
machine with the sound card which mixes all inputs from the nodes and
puts the result out on the sound card outputs. For WFS it could for
example be 20 megabit/s broadcast and total of 400 megabit/s of
unicast.
A separate issue for your "many streams"
case is synchronizing
the streams to each other, in the case where not all share the
same nominal clock. RTP has tools for this, based on
associating NTP timestamps from a common clock to each
independent stream, that get used for audio/video lipsync,
and can be repurposed here as well.
RTP is designed to transport realtime data over a routed network, when
packets can be lost, re-ordered and stuff like that. In the controlled
ethernet environment for this system there will be no packet losses (I
hope), and no reordering.
It would probably work in the way that a roundtrip time is tuned and
found at startup, and then that is added with some marigin to the
I/O-delay in the sound card machine. That is probably quite easy. A
small challenge will be to synchronise dynamic commands such as filter
changes and such, so they happen in the same block index (synchronised)
for all nodes. By specifying block index in the command,
synchronisation will be easily kept though, then the problem is just to
make the command reach all nodes in time. The simple way is to have
quite high latency for the commands, but one would want to minimise
that.
/Anders
7:17 a.m.
On Thu, 15 Apr 2004 12:07:07 +0200
Anders Torger <torger(a)ludd.luth.se> wrote:
Perhaps RTP is good enough. However, at several
hundreds of megabits of
throughput, it could be valuable not needing to calculate checksums in
software. I guess IP and UDP checksums usually are calculated in
software.
That used to be the case but not anymore. Many modern cards to hardware
checksum calculations. I think this is also a prerequisite for zero
copy networking so any card which can do zero copy networking should
also do hardware checksumming.
Erik
--
+-----------------------------------------------------------+
Erik de Castro Lopo nospam(a)mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"Only wimps use tape backup: *real* men just upload their
important stuff on FTP, and let the rest of the world
mirror it ;)" -- Linus Torvalds
8:29 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live music performance toy
Hi Everybody!
I have some old pc hardware that I want to use for live music performance.
To start with it would be an effects box, then if all goes well an expander,
a sampler, and/or whatever other ideas I come up with. I was thinking of
using a footswitch controller, with a few buttons and a wah-wah like pedal
as a knob. I have yet to buy the controller so I'm open to suggestions. It
would work with USB or MIDI, or better both. If MIDI, then I also need a
MIDI input card. Ultimately I would like the software to be as compact as
possible, so I can run it off a flash card instead of a hard drive. It would
probably be without GUI, though I'm leaving this open.
Now to the linux bit:
There is all this cool stuff already programmed for linux that I could be
able to tailor to my needs, so its worth looking at, it seems. And I am sure
I am not the first one to come up with this idea. So would you have any
suggestions on where to start?
As you have probably gathered, I'm a newbie to Linux. But I'm not to
programming, and I'm ok with doing some coding.
bye,
Ariel
9:48 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live music performance toy
On 04/15/04 08:22:41, Ariel Sommeria wrote:
Hi Everybody!
I have some old pc hardware that I want to use for live music performance.
To start with it would be an effects box, then if all goes well an expander,
a sampler, and/or whatever other ideas I come up with. I was thinking of
using a footswitch controller, with a few buttons and a wah-wah like pedal
as a knob. I have yet to buy the controller so I'm open to suggestions. It
would work with USB or MIDI, or better both. If MIDI, then I also need a
MIDI input card. Ultimately I would like the software to be as compact as
possible, so I can run it off a flash card instead of a hard drive. It would
probably be without GUI, though I'm leaving this open.
Now to the linux bit:
There is all this cool stuff already programmed for linux that I could be
able to tailor to my needs, so its worth looking at, it seems. And I am sure
I am not the first one to come up with this idea. So would you have any
suggestions on where to start?
As you have probably gathered, I'm a newbie to Linux. But I'm not to
programming, and I'm ok with doing some coding.
bye,
Ariel
Definitely go MIDI. You just can't go wrong with MIDI, it's always going to
work with everything forever.
As long as whatever controller (conventional or completely insane) you have is
MIDI, you're set. Most all linux audio apps support MIDI control to some
extent, many support MIDI control of almost every possible parameter.
The ones that don't need too anyway, and it shouldn't be too hard a feature to
add.
For a MIDI controlled FX box, you probably want to check out jack-rack (for
simpler chains) or AMS (for arbitrarily complex networks of effects). Both
allow mapping MIDI to most any control (AMS in a really nice easy way too, no
remembering controller numbers etc.)
AMS can supposedly run without a GUI (there's a command line option for it
anyway) even though at a code level the two aren't separated. Not sure about
jack-rack, but I have a feeling it can't.
-Dave
10:27 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live music performance toy
I have a live performance setup I use with my band. I
used one of those tiny VIA motherboards and a Midiman
UNO usb <-> midi adapter.
It seems like it's a good idea to use a flash card and
that's what I did at first, but flash cards peter out
after a certain number of writes. If you want to go
that route, I'd suggest maybe having the partitions
mounted read-only.
--- Ariel Sommeria <asomeria(a)mayah.com> wrote:
Hi Everybody!
I have some old pc hardware that I want to use for
live music performance.
To start with it would be an effects box, then if
all goes well an expander,
a sampler, and/or whatever other ideas I come up
with. I was thinking of
using a footswitch controller, with a few buttons
and a wah-wah like pedal
as a knob. I have yet to buy the controller so I'm
open to suggestions. It
would work with USB or MIDI, or better both. If
MIDI, then I also need a
MIDI input card. Ultimately I would like the
software to be as compact as
possible, so I can run it off a flash card instead
of a hard drive. It would
probably be without GUI, though I'm leaving this
open.
Now to the linux bit:
There is all this cool stuff already programmed for
linux that I could be
able to tailor to my needs, so its worth looking at,
it seems. And I am sure
I am not the first one to come up with this idea. So
would you have any
suggestions on where to start?
As you have probably gathered, I'm a newbie to
Linux. But I'm not to
programming, and I'm ok with doing some coding.
bye,
Ariel
2:43 p.m.
New subject: [linux-audio-dev] OpenAL + portaudio
I'm trying to work with OpenAL and I like how it's
datatypes mesh well with OpenGL, but one thing that I
find quite irritating is the lack of device
enumeration. Would it be difficult to make an
implementation of OpenAL on top of portaudio? I'd be
interested in helping, though I'm not very good with
detailed stuff like this..
11 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live music performance toy
as a knob. I have yet to buy the controller so I'm
open to suggestions. It
Yeah, there are plenty of these out there. I know off the top of my
head that Roland, Yamaha, and Behringer make 'em. I've got a Behringer.
It's cheaper, uses a standard AC power cord, so no wall wart, and has
an extra built in variable pedal. The only issue is that even though
the casing is made out of metal, the pedals themselves are made out of
plastic, tough plastic, but still... it makes me nervous sometimes.
would work with USB or MIDI, or better both. If MIDI,
then I also need a
Hrm, can't think of any USB pedals...
MIDI input card. Ultimately I would like the software
to be as compact as
The most practical midi I/O interfaces I've seen probably come in the
form of breakout boxes. I've seen them in USB, Serial and Parallel
versions. You can also get a cable that breaks out the two midi ports
(in and out) and a joystick port without the midi pins from a standard
PC joystick port. The only thing you've got to watch out for here is
that newer 'soundchip' based 'cards' (this includes most motherboard
audio) or standalone gameport interfaces won't have midi. If you've got
an ISA interface though (don't know how 'old' your hardware is) and an
old sound blaster 16 or somesuch kicking around, those usually have
rather decent midi capabilities. Not only that, but you can usually
find them pretty cheap, or in some 486 somebody threw in the trash, and
they're supported by just about everything ever made (though the sound
output is noiser than a tractor trailer truck). Well, I hope this
helps!
Cheers,
- Mike
16 Apr
16 Apr
3:25 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
Hi everybody,
For a MIDI controlled FX box, you probably want to
check out jack-rack
(for
simpler chains) or AMS (for arbitrarily complex
networks of effects).
Both
I checked on AMS, and it seems that I could use it. I have to look a bit
deeper though.
It seems like it's a good idea to use a flash card
and
that's what I did at first, but flash cards peter out
after a certain number of writes.
I forgot about that 'detail'. 'll
keep the flash card for when IO have
something more mature. It doesn't need to be too rugged to start with.
old sound blaster 16 or somesuch kicking around, those
usually have
rather decent midi capabilities.
MIDI with an old sound blaster sounds like a good
starting point, though I
won't be using it for audio purposes. I even have the old MIDI to gameport
adapter lying around so...
Yeah, there are plenty of these out there. I know off
the top of my
head that Roland, Yamaha, and Behringer make 'em. I've got a Behringer.
I
checked on the Behringer website, and the only MIDI controller stuff I
found was in the 'computer based recording' section, with lots of knobs. I
play sax, so it has to be all controllable by foot. Would you have a product
name?
One more question that comes up:
Would someone have a distro to recommend? Compact and already tuned for
audio/low-latency applications? I've started with SuSE, but I could use
something more light weight...
Thanks for all the help!
Ariel
4:30 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
One more question that comes up:
Would someone have a distro to recommend? Compact and already tuned for
audio/low-latency applications? I've started with SuSE, but I could use
something more light weight...
Thanks for all the help!
Ariel
I think you are looking for Planet CCRMA :
http://ccrma.stanford.edu/planetccrma/software/
->Abstract:
Planet CCRMA (CCRMA is pronounced ``karma'') at Home is a collection of
rpms (RPM stands for RedHat Package Manager) that you can add to a
computer running RedHat 7.3, 8.0, 9 or Fedora Core 1 to transform it
into an audio workstation with a low-latency kernel, current ALSA audio
drivers and a nice set of music, midi, audio and video applications.
Have a lot of fun
Simon
4:46 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
On Fri, Apr 16, 2004 at 09:19:04AM +0200, Ariel Sommeria wrote:
One more question that comes up:
Would someone have a distro to recommend? Compact and already tuned for
audio/low-latency applications? I've started with SuSE, but I could use
something more light weight...
The advantage of SuSE is that the default kernel is already well adapted
to audio work. Don't know about the others. IF you do not need the GUI,
you could probably have quite a 'light' installation. And even with a
GUI, you could e.g. just install WindowMaker, and forget about KDE and
Gnome.
--
FA
5:37 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
On Friday 16 April 2004 09.19, Ariel Sommeria wrote:
[...]
MicroDrive? Not as rugged as a flash card of course, but still compact
(CF II) - and very silent if that matters...
//David Olofson - Programmer, Composer, Open Source Advocate
.- Audiality -----------------------------------------------.
| Free/Open Source audio engine for games and multimedia. |
| MIDI, modular synthesis, real time effects, scripting,... |
`-----------------------------------> http://audiality.org -'
--- http://olofson.net --- http://www.reologica.se ---
It seems like
it's a good idea to use a flash card and
that's what I did at first, but flash cards peter out
after a certain number of writes.
I forgot about that 'detail'. 'll keep the flash card for when IO
have something more mature. It doesn't need to be too rugged to
start with. 
6:35 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
Am Fr, 2004-04-16 um 09.19 schrieb Ariel Sommeria:
One more question that comes up:
Would someone have a distro to recommend? Compact and already tuned for
audio/low-latency applications? I've started with SuSE, but I could use
something more light weight...
Thanks for all the help!
Ariel
Hi,
What about AGNULA ? It can be used by either Red Hat or Debian
installation. It aims to be a small Audio-Developer-Only Distribution,
too. I have not tested it yet. And I don't know if you need to download
either a RH or DEB install-cd, install it and then update the system
with agnula-packages or if AGNULAs ISO-images you can download can boot
and install a working system, so you must find that out on your own :( .
But anyway, hope that helps, too.
URL: http://www.agnula.org/
mfg
Sascha Retzki
7:08 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
Yeah, there
are plenty of these out there. I know off the top of my
head that Roland, Yamaha, and Behringer make 'em. I've got a Behringer.
I
checked on the Behringer website, and the only MIDI controller stuff I 
8:37 a.m.
New subject: [linux-audio-dev]converting old pc hardware to a live musicperformance toy
Le ven 16/04/2004 à 09:19, Ariel Sommeria a écrit :
One more question that comes up:
Would someone have a distro to recommend? Compact and already tuned for
audio/low-latency applications? I've started with SuSE, but I could use
something more light weight...
Thanks for all the help!
Ariel
Several possibilities:
- AGNULA Debian distribution (http://www.agnula.org). It installs on top
of a debian distribution and is probably the best suited for tuning to a
minimal distribution. It also comes now as a Live CD
- Planet CCRMA packages
(http://ccrma.stanford.edu/planetccrma/software/), which you install on
top of a redhat or fedora
- Dynebolic (http://www.dynebolic.org/), also a Live CD
good luck
fd
7466
days inactive
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days old
linux-audio-dev@lists.linuxaudio.org
14 comments
12 participants
participants (12)
-
Alfons Adriaensen -
Anders Torger -
Ariel Sommeria -
Dave Robillard -
David Olofson -
drclaw＠dogsolitude.org -
Erik de Castro Lopo -
Francois Dechelle -
John Lazzaro -
sascha.retzki＠t-online.de -
Simon Schampijer -
Thomas Webb