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Re: noteOn/noteOff and node lifetimes ...

From: lonce wyse <lonce.wyse@zwhome.org>
Date: Mon, 06 Aug 2012 14:28:04 +0800
Message-ID: <501F63F4.6070803@zwhome.org>
To: Chris Rogers <crogers@google.com>
CC: Srikumar Karaikudi Subramanian <srikumarks@gmail.com>, public-audio@w3.org

Hello -

     While I see the issues with having to manage voices (eg overlapping 
note-ons, sending different parameters to different notes), I don't see 
why a good solution is to have AudioBufferSourceNode behave in a manner 
inconsistent with all other Nodes. Not being able to keep references and 
node connections around for reuse for one type of node but not others is 
confusing and makes code hard to manage and read.
     There are other solutions - in a synthesis system I once wrote (not 
unlike webaudio), note on/offs and parameters were given unique IDs so 
that they could be properly matched (there was even a special "all" ID 
so that one could, for example, bend the pitch of all notes with one call).

     Obviously, you don't want to have your average game developer 
keeping track of IDs for notes. But this issue highlights what I see as 
a critical threat to webaudio - that it falling into the classic HCI 
trap of trying to meet the needs of at least two very different groups - 
sound developers and sound users. Sound developers should be trusted to 
create the sounds and systems with user-targeted interfaces as fast as 
webaudio provides developer-strength audio components and 
developer-oriented APIs!

              - lonce

On 8/6/2012 4:53 AM, Chris Rogers wrote:
> On Sat, Aug 4, 2012 at 11:32 PM, Srikumar Karaikudi Subramanian 
> <srikumarks@gmail.com <mailto:srikumarks@gmail.com>> wrote:
>     Yes, I agree that it does seem inconsistent. However, the current
>     "one shot" design has some distinct advantages.
>     Consider the alternatives. If multiple noteOn/noteOff sequences
>     are supported for such source nodes, then there is no obvious
>     answer to how sequences of noteOn/noteOff calls should be handled.
>     For example what should happen for the call sequence "noteOn(1),
>     noteOff(3), noteOn(2)"? Should the second noteOn override
>     the noteOff? Should the noteOff be advanced to happen before the
>     second noteOn? Should the noteOn end up cancelling the scheduled
>     noteOff? etc.  Suppose each noteOn call on such a node is to start
>     a new voice in parallel,  then which of these voices should a
>     noteOff stop - the most recent one or all of them? No particular
>     choice here seems satisfactory or obviously useful to be the default.
>     However, if an "instantiated voice" is reified as a node (as in
>     this "one shot node" design), we get explicit voice level control
>     of the output audio on top of which we can build MIDI-like
>     management mechanisms such as voice stealing or grouping voices
>     into channels if we want. (If we keep a reference around, we
>     can access the state of these nodes and find out that they have
>     finished, since the objects won't be garbage collected.)
> Yes, exactly, and explicit voice control is absolutely essential in 
> order to create independent envelopes (amplitude, pitch, filter, etc.) 
> for each voice.  Because each voice has a one-to-one relationship with 
> a node, we're in a great spot to do this by combining the nodes 
> together to make the synth.  If an AudioBufferSourceNode itself had 
> "internal" multiple voices then we'd be in a very bad place.
>     If we need to feed these voices into a complex signal processing
>     graph that we can't afford to create afresh per voice, then we can
>     hold a reference to the subgraph and send the outputs of the
>     one-shot nodes to the persistent subgraph. (It would then be
>     important to make the overhead of creating and destroying such one
>     shot nodes as low as possible.)
>     For the above reasons, I favour the "voice = one shot node"
>     mapping. But perhaps with better naming of these nodes and the
>     noteOn/noteOff methods, their behaviour can be made clearer? There
>     have been some suggestions such as renaming noteOn/Off to "start"
>     and "stop". Maybe "finish" or "die" might better indicate that
>     "start" cannot be called again. "finish()" would also be
>     consistent with the node's "FINISHED_STATE" enum. Also "source
>     node" is an inadequate description, since we also have
>     "MediaElementSourceNode" and "MediaStreamSourceNode" which don't
>     have this noteOn/Off behaviour.
>     Best,
>     -Kumar
>     On 5 Aug, 2012, at 12:41 PM, lonce wyse <lonce.wyse@zwhome.org
>     <mailto:lonce.wyse@zwhome.org>> wrote:
>>     Hello,
>>     From where I sit, the problem is a usage issue:
>>>     Oscillator and AudioBufferSourceNode
>>>     objects can only be used once through noteOn/noteOff
>>     because it seems inconsistent with the way other nodes can be
>>     used by creating a graph architecture, and "using them more than
>>     once" if you keep a reference to them around.
>>     - lonce
>>     On 5/8/2012 11:00 AM, Chris Rogers wrote:
>>>     On Sat, Aug 4, 2012 at 7:49 PM, Srikumar Karaikudi Subramanian
>>>     <srikumarks@gmail.com <mailto:srikumarks@gmail.com>> wrote:
>>>         Hi all,
>>>         It appears that the Oscillator node's setup code for the
>>>         "basic waveforms" is needlessly run for every node ("voice")
>>>         instantiated. To avoid repeating the waveform setup code,
>>>         can we perhaps delegate the task of creating the basic
>>>         waveforms to the AudioContext object instead of the Oscillator
>>>         node? i.e. AudioContext.createWaveTable(type) can be
>>>         overloaded to return a wave table of the requested basic
>>>         waveform which can then be assigned to any number of
>>>         oscillator nodes.
>>>         Thoughts?
>>>     Hi Kumar, I see you must have been poking around in the WebKit
>>>     source code to see this :)
>>>     You've indeed found an inefficiency in the implementation, and
>>>     might consider filing a WebKit bug about this.  But, it's an
>>>     implementation detail and can be optimized there, without
>>>     needing to modify the API.
>>>     Cheers,
>>>     Chris
Received on Monday, 6 August 2012 06:43:42 UTC

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