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[linux-audio-dev] [admin] music.columbia.edu server downtime

by Joern Nettingsmeier

hi everyone! a happy new year to all folks on the gregorian calendar, and a generic happy next 365 days to everyone else! the music department at columbia university are taking the list server down for an upgrade on the coming weekend, so expect interruptions for linux-audio-dev, linux-audio-user and linux-audio-announce. you will probably want to keep a copy of all the mails you send over the weekend, so that you can re-send them in case they end up in the bit bucket. let me take this opportunity to thank douglas irving repetto for many years of painless hosting and friendly help, and the entire music dept. for their generous donation of iron and bandwidth. kudos, guys! rumor has it that the new list server will be an os x machine. hopefully this will make the lists even more user-friendly and aesthetically pleasing than before ;) all the best, jörn -------- Original Message -------- Subject: music.columbia.edu server downtime Date: Mon, 2 Jan 2006 16:21:13 -0500 From: douglas irving repetto <douglas(a)music.columbia.edu> To: douglas(a)music.columbia.edu Hello, We will be upgrading the music.columbia.edu server this weekend. Hopefully all of the work will be done on Saturday, but it may extend into Sunday. music.columbia.edu will not be available during the downtime. That means no websites will be served, no email will be sent/delivered, no mailing lists will function, etc. I'll send an update later this week with info about some changes that you'll see on the new server. Happy new year, douglas -- ............................................... http://artbots.org .....douglas.....irving........................ http://dorkbot.org ................................ http://ceait.calarts.edu/musicdsp .......... repetto....... http://works.music.columbia.edu/organism ............................... http://music.columbia.edu/~douglas -- jörn nettingsmeier home://germany/45128 essen/lortzingstr. 11/ http://spunk.dnsalias.org phone://+49/201/491621 if you are a free (as in "free speech") software developer and you happen to be travelling near my home, drop me a line and come round for a free (as in "free beer") beer. :-D

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Pedro Lopez-Cabanillas

On Friday 30 December 2005 17:37, Werner Schweer wrote: > The ALSA seq api is from ancient time were no realtime threads were > available in linux. Only a kernel driver could provide usable > midi timing. But with the introduction of RT threads the > ALSA seq api is obsolete IMHO. I don't agree with this statement. IMHO, a design based on raw MIDI ports used like simple Unix file descriptors, and every user application implementing its own event schedule mechanism is the ancient and traditional way, and it should be considered obsolete now in Linux since we have the advanced queueing capabilities provided by the ALSA sequencer. You guys are talking here about MIDI timing, considering only the event scheduling point of view, as if Rosegarden or MusE were simple MIDI players. Of course, playing beats on time is a required feature. But my bigger concern about MIDI timing issues is when you are *recording* events. Here is where ALSA queues, providing accurate timestamps for incoming events, are so good. It could be the absolute winner if problems like the audio synchronization and slave MTC synchronization were solved likewise. Regards, Pedro

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Pedro Lopez-Cabanillas

On Saturday 31 December 2005 17:10, Paul Davis wrote: > On Fri, 2005-12-30 at 22:27 +0100, Pedro Lopez-Cabanillas wrote: > > On Friday 30 December 2005 17:37, Werner Schweer wrote: > > > The ALSA seq api is from ancient time were no realtime threads were > > > available in linux. Only a kernel driver could provide usable > > > midi timing. But with the introduction of RT threads the > > > ALSA seq api is obsolete IMHO. > > > > I don't agree with this statement. IMHO, a design based on raw MIDI ports > > used like simple Unix file descriptors, and every user application > > implementing its own event schedule mechanism is the ancient and > > traditional way, and it should be considered obsolete now in Linux since > > we have the advanced queueing capabilities provided by the ALSA > > sequencer. > > low latency apps don't want queuing they just want routing. this is why > the ALSA sequencer is obsolete for such apps. frank (v.d.p) had the > right idea back when he started this, but i agree with werner's > perspective that the queuing facilities are no longer relevant, at least > not for "music" or "pro-audio" applications. Many professional musicians want MIDI capabilities on their PCs because they already own (or want to have) electronic musical instruments communicating via MIDI. This means that the computer is another piece of musical equipment in the musician's studio/network. The kind of scenario you are painting about low latency applications seems limited to soft synths listening to sequencing applications. Using MIDI to this kind of communication between two processes running in the same machine looks a bit overkill to me. MusE has synth plugins, and Rosegarden has DSSI synth plugins, without ALSA sequencer being involved here. > > It could be the absolute winner if problems like the audio > > synchronization and slave MTC synchronization were solved likewise. > > what problems? JACK demonstrates perfect audio sync in the only sensible > way there is (the same way every other system does it); several JACK > clients have MTC slave capabilities, including ardour, and it has > nothing whatsoever to do with the ALSA sequencer. Exactly. Please, excuse me my poor English. I mean functionality instead of problem. Let me reword the sentence: ALSA could be even better if there were another universal mechanism available for every ALSA application, providing an easy and consistent way to synchronize a queue with an external MTC master, without needing to recode the whole process for each application. I know that Ardour provides slave MTC synchronization, and also does Rosegarden. Each one uses a different approach, and in the future there will be many more better or worse implementations. I like the way Rosegarden solves it, using the ALSA sequencer queue skew parameter. I guess that we can build another ALSA sequencer client, either a kernel module or a userspace one, accepting MTC input and translating the MTC sysex messages received to skew in some queues used also by any other ALSA clients. Comments? Regards, Pedro

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Chris Cannam

Paul Davis: > i guess it all depends on one's definition of > "sufficient". my take is that there are several MIDI > h/w boxes that guarantee MIDI delivery to a > resolution that matches the wire protocol > (1/3msec). until we have scheduling capabilities that > match this (or better), i don't feel comfortable > calling them "sufficient". Ah, I see. I've no argument with that, but it isn't quite what I thought you were referring to. Chris

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Pedro Lopez-Cabanillas

On Saturday 31 December 2005 00:52, Florian Schmidt wrote: > All of this depends on whether physical port midi activity is really > handled by IRQ's too. Anyone know more? I don't know every MIDI interface details, but there are many different variations. Please, somebody with better knowledge could provide additional info and correct my very probable mistakes. USB MIDI interfaces don't generate interrupts. Instead, this is done by the USB host controller (EHCI/OHCI/UHCI). The driver for these devices provide an interrupt handler not directly, but indirectly (the in/out URB completion handlers). So yes, this device type may be considered interrupt-driven. The oldest MIDI interface for PCs was the Roland MPU-401. It had two operational modes: Intelligent and UART mode. Intelligent mode was necessary because the low power of early personal computers CPUs. This intelligent mode required IRQ handlers for both MIDI input and output operations, and to control the internal timer used for hardware scheduling and event timestamping, and also for external MTC/SMPTE synchronization. It was a rather sofisticated piece of hardware, but there is not an ALSA driver for these devices (and I don't know a single manufacturer selling it nowadays). The MPU-401 UART mode doesn't provide an interrupt signal to finish the output completion, so you must use polling for output (it provides an interrupt only for incoming events). There is an ALSA driver for this mode, that is used also by many consumer sound cards emulating the MPU-401. I wouldn't recommend to use these MIDI interfaces. Other chips, as the Ensoniq 1370/1371 used in some cheap SoundBlaster products, included a better UART mode, providing interrupts for both reception and transmission. There is also an ALSA driver for the 16550 UART, that can be used with a few external devices like the Roland Canvas and the Midiator devices. Regards, Pedro

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Chris Cannam

Paul Davis: > most of the ALSA sequencer's > capabilities are redundant, which is compounded > because it currently has > no way of providing sufficiently accurate scheduling You say this as if it were self-evident, when it's been the subject of much of this thread. _Does_ it have no way of providing sufficiently accurate scheduling? If not, why not? This would imply that there is in fact no way for a userspace application on a normal Linux distribution to provide MIDI timing accurate enough to be perceived as correct in all circumstances. Chris

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Chris Cannam

Paul Davis: > frank (v.d.p) had the right idea back when he > started this Huh? Started what? Chris

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Chris Cannam

Me: > I'll have to review the sequencer API and look at > adding a separate RT MIDI thread as an alternative Actually no, hang on a minute. First I want to know more about why the ALSA sequencer queue doesn't work better here. It's all very well saying it's irrelevant now that it's so easy to create RT threads, but I think that's bogus. Probably a substantial majority of Rosegarden users doing MIDI only are using systems on which it isn't possible for a random user to create RT threads at all. For these users, the ALSA sequencer ought to be able to do a lot better than an ordinary unprivileged thread can. I'd like to know why it might not. I'm not at a proper computer just now, to delve through code - anyone have any more idea about this? Chris

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Chris Cannam

Florian Schmidt: > Yeah, i got a nice and juicy BUG in it (see below). So > this is what kills rosegarden regularly here when > run with RTC timing source. That'll be the chap. Mind you, I never saw the RTC- based timer measure significantly better than the system timer at 1000Hz. Although your measurements may vary, and it seems, probably would. Chris

19 years, 10 months

Re: [linux-audio-dev] Audio/Midi system - RT prios..

by Chris Cannam

Florian Schmidt writes: > Here's example output with rosegarden producing a > supposedly steady stream of 16th notes at 120 bpm: > [...] Those results certainly are pretty poor. We do have a very similar test in the Rosegarden tree (the complainer test) but it doesn't stress the system quite the way it seems your program does. I'll have to review the sequencer API and look at adding a separate RT MIDI thread as an alternative (which should be straightforward enough). The rationale for using queued events is simple -- ALSA provides the service, why duplicate it? -- but it's probably true that we've already spent far more time working around problems with it than we saved by not duplicating it. (Does anyone else use queued sequencer events in earnest?) Chris

19 years, 10 months

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