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Re: Help needed with a sync-problem

From: Chris Wilson <cwilso@google.com>
Date: Fri, 3 Aug 2012 10:21:55 -0700
Message-ID: <CAJK2wqU96Ju0Xzdq9PzEkoxKC2YT9WyuFBhzQSKqk0o7PZ6bSw@mail.gmail.com>
To: Jussi Kalliokoski <jussi.kalliokoski@gmail.com>
Cc: Peter van der Noord <peterdunord@gmail.com>, Adam Goode <agoode@google.com>, public-audio@w3.org
How would you empower the JS node/DSP API to fix this?

I still think, personally, that there's an awful lot of focus on custom
processing in our discussions here.  I haven't felt the need to build a
JSNode yet - the first one I will build is probably a noise gate/expander,
since that's the only thing I can't easily replicate from the nodes already
available.  I'm not really convinced that what most application developers
want to do - NEED to do - is process audio bits themselves directly.

On Fri, Aug 3, 2012 at 10:11 AM, Jussi Kalliokoski <
jussi.kalliokoski@gmail.com> wrote:

> It's a known and major issue all right, but it's not a bug. There's not
> much that can be done about it though, afaict. The processing thread has to
> buffer enough data (the buffer size) from the inputs of the JSNode before
> its callback can be invoked, and next it just sends an event to the JS
> thread to process the buffer. The audio thread, however, can't wait for the
> JS thread to process the buffer but instead plays back the previously
> processed buffer.
>
> This is one of the reasons why I think we should focus on empowering the
> JS node / DSP API. If you want to add any custom processing to the graph,
> you're going to have to adjust the rest of the graph accordingly and you'll
> end up with more latency. This means that if you want to do extensive
> custom processing you'll probably need to work around the graph or just go
> with just the JS and have your own routing which means you're in a much
> more flexible place already anyway. I think the graph serves best as an IO
> abstraction, and that's the part we should focus on.
>
> Cheers,
> Jussi
>
>
> On Fri, Aug 3, 2012 at 4:16 PM, Peter van der Noord <peterdunord@gmail.com
> > wrote:
>
>> Well, it seems indeed that custom-nodes add a delay-time to the signal.
>> I've connected a few bypass modules (they write their input to the output)
>> and i'm magically creating an echo...
>>
>> http://www.petervandernoord.nl/patchwork_js/?patch=2&buffer_size=8192
>>
>> (to hear sound, you have to select the loaded buffer from the pulldown in
>> the buffersource-module)
>>
>> I'm getting somewhat confused and concerned about this, why does this
>> happen and isn't this a major bug/issue?
>>
>> Peter
>>
>>
>>
>> 2012/8/2 Adam Goode <agoode@google.com>
>>
>>> I think you can use playbackTime to determine the absolute a-rate time
>>> of the beginning of the javascript buffer. But last I checked it wasn't
>>> present in webkit.
>>>
>>> You might be able to count samples, assuming you know the node's noteOn
>>> time, to keep track of the a-rate time. But with a short buffer size,
>>> sometimes you can have problems as you've noticed.
>>>
>>>
>>> On Thu, Aug 2, 2012 at 4:47 PM, Peter van der Noord <
>>> peterdunord@gmail.com> wrote:
>>>
>>>> Ermmm.....wait, what? And that is intened behavior?
>>>>
>>>> Peter
>>>>
>>>>
>>>> 2012/8/2 Jussi Kalliokoski <jussi.kalliokoski@gmail.com>
>>>>
>>>>> Hey Peter!
>>>>>
>>>>> I think this is because the JSNode has a delay equivalent to the
>>>>> buffer size, hence if you have parallel graphs that contain a different
>>>>> number of JSNodes, they will arrive to the common destination at a
>>>>> different delay.
>>>>>
>>>>> Cheers,
>>>>> Jussi
>>>>>
>>>>>
>>>>> On Thu, Aug 2, 2012 at 11:35 PM, Peter van der Noord <
>>>>> peterdunord@gmail.com> wrote:
>>>>>
>>>>>> I'm having a strange problem with some signals at the moment and i've
>>>>>> been staring at it for way too long now, so i thought: why not put it up
>>>>>> here, maybe someone sees what's going on. It's a lenghty story, so if you
>>>>>> want to hang on...i'll try to explain :)
>>>>>>
>>>>>> As you may know, i'm writing a modular synthesizer:
>>>>>>
>>>>>> http://petervandernoord.nl/patchwork_js (maybe clear your cache if
>>>>>> you've been there before)
>>>>>>
>>>>>> If you click the 'json to patch' button, a testpatch will be set.
>>>>>> (Important to know: all custom nodes will be created with the buffer-size
>>>>>> that's selected in the pulldown on the right). The patch contains 3 modules
>>>>>> (in patchwork, a module can contain one or more audionodes, with the
>>>>>> module's in/outputs mapped to certain in/outputs of the containing nodes):
>>>>>>
>>>>>> - The destination, which contains a normal destinationNode
>>>>>> http://localhost/patchworkjs/js/modules/DestinationModule.js
>>>>>>
>>>>>> - a clockmodule. one custom js node
>>>>>> http://localhost/patchworkjs/js/modules/DestinationModule.js
>>>>>>
>>>>>> - a triggersequencer, also one custom node.
>>>>>> http://localhost/patchworkjs/js/modules/TriggerSequencerModule.js(the audioprocess callback is at the bottom)
>>>>>>
>>>>>> What is happening in the patch: the clock sends out single values
>>>>>> of 1s (all other values are 0) on a given interval (set in BPM). The
>>>>>> sequencer checks on every incoming value if that value is >0 AND the
>>>>>> previous one was <=0 (i'll call that a clock-pulse). If that is the case,
>>>>>> its SequencerParameter will proceed to the next step. A sequencer-parameter
>>>>>> (actually it is a LogicSequencerParameter, but that's almost the same - it
>>>>>> has one extra method) can be found here:
>>>>>>
>>>>>> http://localhost/patchworkjs/js/params/SequenceParameter.js
>>>>>>
>>>>>> It's basically just an array filled ith 0s and 1s (you can set a 1 by
>>>>>> clicking somewhere on the sequencer), and increases the current position
>>>>>> when it gets a next() command. So, back to the the sequencer module: If it
>>>>>> received a clock-pulse, it proceeds the sequencer. Then, if the (new) value
>>>>>> of the sequencer-parameter is 1, the sequencer will write a 1 in its
>>>>>> outputbuffer as well.
>>>>>>
>>>>>> My issues:
>>>>>> - in the testpatch, both the clockmodule and the seq-module are
>>>>>> connected to the output. if you activate some steps in the sequencer, you
>>>>>> will hear that the clicks do not run in sync. I have no idea why that is,
>>>>>> the stepsequencer writes a 1 in exact the same iteration as it reads the
>>>>>> incoming 1s from the clock. In my opinion, they should run exactly in sync.
>>>>>> - When you change the buffersize (which is for the customnodes) you
>>>>>> will hear that the timedifference between the ticks changes (since there's
>>>>>> no clear, you have to refresh the page, set another buffersize and click
>>>>>> 'json to patch')
>>>>>> - Something else i noticed: when i run just a clock module connected
>>>>>> to the output, with a very low buffersize (256, 512), the clock seems to
>>>>>> run very, very irregular.
>>>>>>
>>>>>>
>>>>>> So, my main question: Does anyone have any idea why those two modules
>>>>>> do not run in sync when both connected to the output?
>>>>>>
>>>>>>
>>>>>> Peter
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
Received on Friday, 3 August 2012 17:22:25 GMT

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