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Re: MIDI synchronization issues

From: James Ingram <j.ingram@netcologne.de>
Date: Sun, 30 Sep 2012 18:26:25 +0200
Message-ID: <506872B1.5050802@netcologne.de>
CC: Chris Wilson <cwilso@google.com>, public-audio@w3.org, Jussi Kalliokoski <jussi.kalliokoski@gmail.com>, Joseph Berkovitz <joe@noteflight.com>
I've now updated the tick() function (both in the code and in the gist) 
and the sound has indeed improved.
Among other things, the hairpin in bar 1 of Study 2c3.1 is now working 
properly! :-))
Sorry to have cast aspersions on Jazz! Mea culpa!

The synchronization issues are still there.

all the best,

Am 30.09.2012 17:11, schrieb James Ingram:
> ooops. Sorry.
> Just discovered a serious bug in my version of the tick() function.
> Why do such things always happen just after hitting the send button?
> I don't think this affects the synchronization issues, but it may well 
> have something to do with the sound of the output.
> Hope to have a correction out within a couple of hours.
> j.
> Am 30.09.2012 13:49, schrieb James Ingram:
>> Hi Chris, Jussi, Joe, all,
>> I have now implemented a Sequence object, and am using it in [1].
>> This program is a "work in progress" and does not yet implement MIDI 
>> Input, but it can be used to play back SVG-MIDI scores. For usage, 
>> see [2].
>> I had to make a few changes to Chris's tick() function, and have run 
>> into a couple of synchronization issues. My current tick() function 
>> [3] depends on PREQUEUE being 0. If PREQUEUE were to be increased, 
>> exact synchronization with the score would deteriorate. There would 
>> be no way of knowing exactly when the MIDIMessage is really sent. 
>> Something needs to be done to ensure that exact synchronization will 
>> always be possible. There will be other things that need to be 
>> synchronized with MIDIMessages, not just running cursors. Another 
>> problem is the current non-existence of empty messages.
>> This is not really my sphere, but it might help to understand the 
>> problem if I say where I'd start looking for a solution:
>> 1. MIDIMessages could have an optional callback, to be called at 
>> their actual send time. But that would not work for rests. Rest 
>> messages are currently never sent to the MIDI output device at all. 
>> Maybe we need a wrapper for MIDIMessages which would include both the 
>> callback and the information that this is an empty message. Empty 
>> messages need to be part of the spec too. If you are not convinced, 
>> try playing a track containing just simple notes and rests. Rests 
>> sometimes contain note-off messages, but sometimes they are really 
>> EMPTY (e.g. when two rests are separated by a barline).
>> 2. Currently, MIDI programmers/libraries can set the value of 
>> PREQUEUE themselves, allowing different applications to be given 
>> optimal values. What, precisely, are the pros and cons of having 
>> larger values?
>> Maybe the following belongs in a separate thread, but I'd like to 
>> mention it anyway:
>> I'm currently not entirely happy with the sound of the output (its 
>> not always exactly the same, and it sounds rather scratchy compared 
>> to playing the same scores in C#).
>> I know I'm pushing things a bit, but I suspect that Jazz is a bit 
>> slow, especially when it comes to sending continuous controller info 
>> (I'm currently testing Jazz's speed). For example, the first 
>> (ornamented) chord in track 1 of Study 2c3.1 contains repeated notes 
>> and a simple expression hairpin (cresc.-dim.) but, if the hairpin is 
>> played at all, it is not being performed as smoothly as the MIDI info 
>> says it should. Also, the tracks in Study 3 sketch don't sound as 
>> they should (there's an mp3 at [4]). This is only a sketch, and the 
>> tracks in bar 1 are really only tests, which should be played 
>> separately...
>> As I said, I think its a Jazz problem. I don't think its my 
>> javascript because these things do sometimes work better. Are you 
>> sure it is not a problem with Javascript itself?
>> all the best,
>> James
>> [1] 
>> http://james-ingram.de/tests/AssistantPerformer_W3CAudio/AssistantPerformer.html
>> [2] usage:
>> To start, just select a score and MIDI output device (optionally 
>> setting the speed option) and hit "Start".
>> The controls along the top of the score should be fairly self 
>> explanatory. From left to right:
>> 1. track selector (= staves, in top to bottom order).
>> 2. player controls:
>>     a) go, pause, paused
>>     b) stop
>>     c) set start position tool
>>     d) set end position tool
>>     e) send start position to beginning of score (default position)
>>     f) send end position to end of score (default position)
>> 3. (currently disabled) toggles between playing live and playing the 
>> MIDI stored in the score
>> 4. set options: click this to reset the options in the upper dialog.
>> [3] https://gist.github.com/3806262
>> [4] 
>> http://james-ingram-act-two.de/compositions/sketches/study3Sketch/scores/Study%203%20sketch%201%20score/Study%203%20sketch%201.html 

Received on Sunday, 30 September 2012 16:27:09 UTC

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