Subject: Re: [linux-audio-dev] a new application underway
From: Paul Barton-Davis (pbd_AT_Op.Net)
Date: pe loka 08 1999 - 19:35:14 EDT
>Of course there's no way to get kernel space real time performance
>with a user space engine... As the ALSA sequencer is in kernel space,
>so would any other solution have to be, at least if it's about
>*latency* - accuracy is completely different, unless you're
>controlling something that doesn't support timestamps...
>But what would the ALSA sequencer automate then? In what way does
>it't timing accuracy help? External MIDI devices won't benefit from
>better than ms accuracy.
the scenario in which the sequencer helps is simple: suppose that
you're a program that is *not* currently generating samples and *not*
using the RTC, but basically asleep, doing a select(2) or poll(2) on a
whole set of various file descriptors. Our automation recording wants
us to wake up at a certain point and do something.
Currently, you can only get 20ms or so accuracy on this from user
space in the scenario I describe. If the ALSA sequencer can do
flexible time scheduling, then you can ensure that you will be woken
up at exactly the right moment.
What kind of program does this ? Well, certainly most audio applications
don't need this, because they have the DAC to provide a time sync
source. But pure MIDI apps don't have this, and so the sequencer is
very useful for them. Programs that typically don't continuously
output samples would also benefit from it.
Even something like the hdr mixer I'm working on, not having to think
about accurate timing but instead relying on the source of automation
info to ensure that I am delivered events at the right time makes the
code a lot simpler.
>Well, I thought we were actually to *use* the plug-in API... One of the *BIG*
I was jesting :)
>Besides, MIDI automation won't do for non-destructive hard disk
>editing,
tell that to Mackie&Digidesign: the HUI and ProTools collaborate in
exactly this way (well, i don't know how exactly, because I don't know
whether ProTools stores the automation events as MIDI data or using
its own event format).
>and if there's one thing I hate, it's multiple similar
>systems that are supposed to cooperate. (Reminds me of M$ style
>design... ;-)
agreed.
This archive was generated by hypermail 2b28 : pe maalis 10 2000 - 07:27:13 EST