[linux-audio-dev] Catching up with XAP

[Lost touch with the list, so I'm trying to catch up here... I did notice that gardena.net is gone - but I forgot that I was using david(a)gardena.net for this list! *heh*] Sure. I just don't see why it would be useful, or why the VVID subsystem should be turned into some kind of synth status API. No. Only the one who *allocated* a VVID can free it - and that means the sender. If *you* allocate a VVID, you don't want the host to steal it back whenever the *synth* decides it doesn't need the VVID any more. You'd just have to double check "your" VVIDs whenever you send events - and this just to support something that's really a synth implementation detail that just happens to take advantage of a host service. No, you just need to find the next VVID that *you're* not using, and reassign that to a new context. (ALLOC_VVID or whatever.) You don't really care whether or not the synth's version of a context keeps running for some time after you stop sending events for context; only the synth does - and if you're not going to send any more events for a context, there's no need to keep the VVID. VVIDs can't end spontaneously. Only synth voices can, and VVIDs are only temporary references to voices. A voice may detach itself from "it's" VVID, but the VVID is still owned by the sender, and it's still effectively bound to the same context. BTW, this means that synths should actually keep the voice control state for a VVID until it actually knows the context has ended. Normally, this just means that voices don't really detach themselves from VVIDs, but rather just go to sleep, until stolen or woken up again. That is, synths with "virtual voices" might actually have use for a "DETACH_VVID" event. Without it, they basically have to keep both real and virtual voices indefinitely. Not sure it actually matters much, though. Performance wise, it just means you have to deal with voice controls and their ramping (if supported). And since a ramp is actually two events (ramp event with "aim point" + terminator event or new ramp event), and given that ramping across blocks (*) is not allowed, it still means "no events, no processing." (*) I think I've said this before, but anyway: I don't think making ramping accross block boundaries illegal is a good idea. Starting a ramp is actually setting up a *state*. (The receiver transforms the event into a delta value that's applied to the value every sample frame.) It doesn't make sense to me to force senders to explicitly set a new state at the start of each block. Indeed, the fact that ramping events have target and duration arguments looks confusing, but really, it *is* an aim point; not a description of a ramp with a fixed duration. If this was a perfect world (without rounding errors...), you would have sent the delta value directly, but that just won't work in real life. If someone can come up with a better aim point format than <target, duration>, I'm all ears, because it really *is* confusing. It suggests that RAMP events don't behave like SET events, but that's just not the case. The only difference is that RAMP events set the internal "dvalue", while SET events set the "value", and zero "dvalue". The plugin is *not* ignoring them. It may route them to a "null voice", but that's basically an emergency action taken only when running out of voices. Normally, a synth would keep tracking events per VVID until the VVID is explicitly detached (see above), or the synth steals whatever object is used for the tracking. Again, DETACH_VVID might still be a good idea. Synths won't be able to steal the right voices if they can't tell passive contexts from dead contexts... [...] Well, you don't need a *real* voice until you need to play sound, do you? Either way, the distinction is a matter of synth implementation, which is why I think it should be "ignored" by the API. The API should not enforce the distinction, nor prevent synths from making use of the distinction. Yes, it's event ordering messed up. This will never happen unless the events are *created* out of order, or mixed up by some event processor. (Though, I can't see how an event processor could reorder incoming events while doing something useful. Remember; we're talking about real time events here; not events in a sequencer database.) Why? So it can "automatically" reorder events at some point? Indeed, users, senders and some event processors might need to know which events are "triggers", and which events are latched rather than continous. For example, my Wacom tablet would need to know which of X, Y, X-tilt, Y-tilt, Pressure and Distance to send last, and as what voice control. It may not always be obvious - unless it's always the NOTE/VOICE/GATE control. The easiest way is to just make one event the "trigger", but I'm not sure it's the right thing to do. What if you have more than one control of this sort, and the "trigger" is actually a product of both? Maybe just assume that synths will use the standardized NOTE/VOICE/GATE control for one of these, and act as if that was the single trigger? (It would have to latch initializers based on that control only, even if it doesn't do anything else that way.) [...] Right, but I'm not even sure there is a reason why they should be aware of VVIDs. What would a mono synth do with VVIDs that anyone would care about? This is very "anti modular synth". NOTE/VOICE/GATE is a control type hint. I see no reason to imply that it can only be used for a certain kind of controls, since it's really just a "name" used by users and/or hosts to match ins and outs. Why make Channel and Voice controls more different than they have to be? * Channel->Channel: * Voice->Voice: Just make the connection. These are obviously 100% compatible. * Voice->Channel: Make the connection, and assume the user knows what he/she is doing, and won't send polyphonic data this way. (The Channel controls obviously ignore the extra indexing info in the VVIDs.) * Channel->Voice: This works IFF the synth ignores VVIDs. You could have channel/voice control "mappers" and stuff, but I don't see why they should be made more complicated than necessary, when in most cases that make sense, they can actually just be NOPs. About VVID management: Since mono synths won't need VVIDs, host shouldn't have to allocate any for them. (That would be a waste of resources.) The last case also indicates a handy shortcut you can take if you *know* that VVIDs won't be considered. Thus, I'd suggest that plugins can indicate that they won't use VVIDs. [...] Right, then we agree on that as well. What I mean is just that "end a voice" doesn't *explicitly* kill the voice instantly. What might be confusing things is that I don's consider "voice" and "context" equivalent - and VVIDs refer to *contexts* rather than voices. There will generally be either zero or one voice connected to a context, but the same context may be used to play several notes. That just won't work. You don't want continous pitch and stuff to work except when the note is on? Stopping a note is *not* equivalent to releasing the context in which it was played. Another example that demonstrates why this distinction matters would be a polyphonic synth with automatic glisando. (Something you can hardly get right with MIDI, BTW. You haveto use multiple monophonic channels, or trust the synth to be smart enough to do the right thing.) Starting a new note on a VVID when a previous note is still in the release phase would cause a glisando, while if the VVID has no playing voice, one would be activated and started as needed to play a new note. The sender can't reliably know which action will be taken for each new note, so it really *has* to be left to the synth to decide. And for this, the lifetime of VVIDs/contexts need to span zero or more notes, with no upper limit. Nope, not unless *both* the synth and the sender have released the VVID. If the host/sender doesn't sent VOICE_OFF when needed, it's broken, just like a MIDI sequencer that forgets to stop playing notes when you hit the stop button. And yes, this is another reason to somehow mark the VOICE/NOTE/GATE control as special. VOICE_OFF and DETACH *have* to be separate concepts. (See above.) It would have to send note off as well I think, or we'd have another special case to make all senders compatible with all synths. (And if "note on" is actually a change of the VOICE/GATE control from 0 to 1, you *have* to send an "off" event as well, or the synth won't detect any further "note on" events in that context.) It may be wasteful to use real, active voices just to track control changes, but voice control tracking cannot be avoided. Who says? I think that sounds *very* much like a synth implementation thing - but point taken; "GATE" is probably not a good name. [...] In fact, on some MIDI synths, you have to assume it is, sort of. Sending a PC to a Roland JV-1080 has it instantl kill any notes playing on that channel, go to sleep for a few hundreds of a second, and then process any events that might have arrived for the channel during the "nap". This really sucks, but that's the way it works, and it's probably not the only synth that does this. (The technical reason is most probably that spare "patch slots" would have been required to do it in any other way - and as I've discovered with Audiality, that's not as trivial to get right as it might seem at first. You have to let the old patch see *some* of the new events for the channel, until the old patch decides to die.) AWE, Live! and Audigy cards don't do it this way - but PC is *still* not an ordinary control. Playing notes remain controlled by the old patch until they receive their NoteOffs. PC always has to occur *before* new notes. Either way, MIDI doesn't have many voice controls at all, and our channel controls are more similar to MIDI (Channel) CCs in some ways. (Not addressed by note pitch, most importantly.) That is, they can't be compared directly - but the concept that some controls must be sent before they're latched to have the desired effect is still relevant. [...] I see why you don't like this. You're forgetting that it's the *value* that is the "initializer" for the VOICE_OFF action; not the SET event that brings it. Of course the plugin "knows" - the last set put a new value into the control that the VOICE_OFF action code looks at! :-) A synth is a state machine, and the events are just what provides it with data and - directly or indirectly - triggers state changes. We have two issues to deal with, basically: 1. Tracking of voice controls. 2. Allocation and control of physical voices. The easy way is to assume that you use a physical voice whenever you need to track voice controls, but that's just an assumption that a synth author would make to make the implementation simpler. It doesn't *have* to be done that way. If 1 and 2 are handled as separate things by a synth, 2 becomes an implementation issue *entirely*. Senders and hosts don't really have a right to know anything about this - mostly because there are so many ways of doing it that it just doesn't make sense to pretend that anyone cares. As to 1, that's what we're really talking about here. When do you start and stop tracking voice controls? Simple: When you get the first control for a "new" VVID, start tracking. When you know there will be no more data for that VVID, or that you just don't care anymore (voice and/or context stolen), stop tracking. So, this is what I'm sugesting ( {X} means loop X, 0+ times ) : * Context allocation: // Prepare the synth to receive events for 'my_vvid' send(ALLOC_VVID, my_vvid) // (Control tracking starts here.) { * Starting a note: // Set up any latched controls here send(CONTROL, <whatever>, my_vvid, <value>) ... // (Synth updates control values.) // Start the note! send(CONTROL, VOICE, my_vvid, 1) // (Synth latches "on" controls and (re)starts // voice. If control tracking is not done by // real voices, this is when a real voice would // be allocated.) * Stopping a note: send(CONTROL, <whatever>, my_vvid, <value>) ... // (Synth updates control values.) // Stop the note! send(CONTROL, VOICE, my_vvid, 0) // (Synth latches "off" controls and enters the // release phase.) * Controling a note (even in release phase!): send(CONTROL, <whatever>, my_vvid, <value>) // (Synth updates control value.) } * Context deallocation: // Tell the synth we won't talk any more about 'my_vvid' send(DETACH_VVID, my_vvid) // (Control tracking stops here.) This still contains a logic flaw, though. Continous control synths won't necessarily trigger on the VOICE control changes. Does it make sense to assume that they'll latch latched controls at VOICE control changes anyway? It seems illogical to me, but I can see why it might seem to make sense in some cases... //David Olofson - Programmer, Composer, Open Source Advocate .- The Return of Audiality! --------------------------------. | Free/Open Source Audio Engine for use in Games or Studio. | | RT and off-line synth. Scripting. Sample accurate timing. | `---------------------------> http://olofson.net/audiality -' --- http://olofson.net --- http://www.reologica.se ---