Re: scheduling subgraphs

Yes, I can see that if such a JS wrapper were to encapsulate the  
AudioContext along with some notion of transforms, that would probably  
work. One could build a "smarter context" that incorporates a notion  
of transformation.  I will most likely be persuaded when I see a  
sketch of the alternative that you're proposing.

The other issue of scheduling programmatic audio generation seems  
separate from this, and I think it's a higher priority to resolve it.

...joe

On Oct 19, 2010, at 3:33 PM, Chris Rogers wrote:

> Hi Joe,
>
> As we discussed a little bit in the tele-conference on Monday, my  
> strategy has been to create an API which is as lightweight and  
> concise as possible while still allowing for efficient native  
> processing, easy graph construction, and low-latency playback.  I  
> can definitely see where the concepts of time-offset can be useful  
> when building complex sequencing applications, but I believe that it  
> is very straightforward to create JS sequencing wrapper classes to  
> encapsulate the time-offset.  The user of this class would not need  
> to worry about passing in the time-offset to every method call,  
> because the implementation of the class would take care of the  
> details.  Exactly what the API of this JS sequencing class looks  
> like would depend on the details of the sequencing application  
> (traditional sequencer, loop-based, region-based digital-audio  
> workstation timeline, etc.), so I'm hesitant to build in anything  
> more complex into the base API other than what is necessary.
>
> As we have more time to play with the API and build more sequencing  
> applications, then I may be proven wrong.  But I'd like to have a  
> chance to see how different kinds of sequencing wrapper classes can  
> solve different use cases.
>
> Chris
>
>
>
> On Mon, Oct 18, 2010 at 6:56 PM, Joseph Berkovitz  
> <joe@noteflight.com> wrote:
> On the subgraph-scheduling topic that we discussed on the call  
> today, we resolved that we'd work through some code examples to  
> understand the issue of subgraph scheduling better.  I would like to  
> try to take a first step on this. If it doesn't feel valuable to go  
> further with it, then I'll be fine with moving on!
>
> The issue for me is that I would like to be able to define a "local  
> time origin" that is used to transform all time values used by  
> noteOn(), startAt(), automateAt()... basically, most functions that  
> care about time.  Right now these are all scheduled relative to an  
> "absolute time origin" that is associated with the owning  
> AudioContext, which I feel is a bit inconvenient and requires extra  
> parameters in every function in the call tree that makes a node graph.
>
> This feels to me like it's a low-impact thing to implement -- but  
> only if people feel it's worth it.  Let me make a concrete proposal  
> that seems cheap and easy, and try to show how it affects couple of  
> simple use cases.  My proposal is adapted directly from the notion  
> of transforms in the HTML5 Canvas specification, and consists of  
> three functions on AudioContext: offset(), save(), restore().   
> AudioContext also acquires a new attribute: "currentOffset". Here  
> are their definitions:
>
>  Object transform: an Object with a numeric "offset" property which  
> affects any time-based property of an object created from this  
> AudioContext. Other properties could be added, e.g "gain". The idea  
> is that these are properties that make sense to affect a wide array  
> of objects.
>  void offset(float delta): adds delta to the value of transform.offset
>  save(): pushes a copy of "transform" onto an internal stack in the  
> AudioContext
>  restore(): pops an object from the same internal stack into  
> "transform"
>
> Implementation concept: The parent AudioContext's currentOffset  
> value is automatically added to any time-valued parameters that are  
> used in scheduling functions on a node, such as noteOn(), etc.
>
> USE CASES
>
> The main difference is simple: with local time offsets saved in the  
> context, one can eliminate a whole bunch of "startTime" parameters  
> that need to be passed through everywhere.  This may not seem like  
> much of a saving, but it feels cleaner to me, and if the spec ever  
> starts to generalize the notion of a saved/restored transform to  
> include other variables besides time (e.g. a "local gain" or "local  
> pan"), it starts really paying off.  You don't want to go back and  
> ask developers to add a whole bunch of new parameters to existing  
> functions and pass all these values through everywhere.
>
> I'm going to give two use cases. The second one builds on the first.
>
> CASE 1. One wishes to play a sequence of audio buffers at some  
> sequence of evenly spaced times starting right now.
>
> Code needed today:
>
> function main() {
>  var context = new AudioContext();
>  playSequence(context, [/* buffers */], 0.25, context.currentTime);
> }
>
> function playSequence(context, bufferList, interval, startTime) {
>  for (var buffer in bufferList) {
>    playBuffer(context, buffer, startTime);
>    startTime += interval;
>  }
> }
>
> function playBuffer(context, buffer, startTime) {
>  node = context.createBufferSource();
>  node.buffer = buffer;
>  node.noteOn(startTime);
>  node.connect(context.destination);
> }
>
> Code needed with time-offset transforms:
>
> function main() {
>  var context = new AudioContext();
>  context.offset(context.currentTime);  // from here on out, all time  
> offsets are relative to "now"
>  playSequence(context, [/* buffers */], 0.25);
> }
>
>
> function playSequence(context, bufferList, interval) {
>  for (var buffer in bufferList) {
>    playBuffer(context, buffer);
>    context.offset(interval);
>  }
> }
>
> function playBuffer(context, buffer) {
>  node = context.createBufferSource();
>  node.buffer = buffer;
>  node.noteOn(0);  // starts relative to local time offset determined  
> by caller
>  node.connect(context.destination);
> }
>
> CASE 2: builds on CASE 1 by playing a supersequence of sequences,  
> with its own time delay between the onset of lower-level sequences.
>
> Code needed today:
>
> function main() {
>  var context = new AudioContext();
>  playSupersequence(context, [/* buffers */], 10, 5.0,  
> context.currentTime);
> }
>
> function playSupersequence(context, bufferList, repeatCount,  
> interval, startTime) {
>  for (var i = 0; i < repeatCount; i++) {
>    playSequence(context, [/* buffers */], 0.25, startTime + (i *  
> interval));
>  }
> }
>
> function playSequence(context, bufferList, interval, startTime) {
>  for (var buffer in bufferList) {
>    playBuffer(context, buffer, startTime);
>    startTime += interval;
>  }
> }
>
> function playBuffer(context, buffer, startTime) {
>  node = context.createBufferSource();
>  node.buffer = buffer;
>  node.noteOn(startTime);
>  node.connect(context.destination);
> }
>
> Code needed with time-offset transforms:
>
> function main() {
>  var context = new AudioContext();
>  context.offset(context.currentTime);
>  playSupersequence(context, [/* buffers */], 10, 5.0);
> }
>
> function playSupersequence(context, bufferList, repeatCount,  
> interval) {
>  for (var i = 0; i < repeatCount; i++) {
>    playSequence(context, [/* buffers */], 0.25);
>    context.offset(interval);
>  }
> }
>
> // Note use of save() and restore() to allow this function to  
> preserve caller's time shift
> function playSequence(context, bufferList, interval) {
>  save();
>  for (var buffer in bufferList) {
>    playBuffer(context, buffer);
>    context.offset(interval);
>  }
>  restore();
> }
>
> function playBuffer(context, buffer) {
>  node = context.createBufferSource();
>  node.buffer = buffer;
>  node.noteOn(0);  // starts relative to local time offset determined  
> by caller
>  node.connect(context.destination);
> }
>
>
> ... .  .    .       Joe
>
> Joe Berkovitz
> President
> Noteflight LLC
> 160 Sidney St, Cambridge, MA 02139
> phone: +1 978 314 6271
> www.noteflight.com
>
>
>
>
>
>
>

... .  .    .       Joe

Joe Berkovitz
President
Noteflight LLC
160 Sidney St, Cambridge, MA 02139
phone: +1 978 314 6271
www.noteflight.com