W3C home > Mailing lists > Public > public-audio@w3.org > July to September 2012

Help needed with a sync-problem

From: Peter van der Noord <peterdunord@gmail.com>
Date: Thu, 2 Aug 2012 22:35:25 +0200
Message-ID: <CAL9tNz_xkmYEVyaOfBPT3iQvazi0EmAXXee-9jV+xX9joZpAnA@mail.gmail.com>
To: public-audio@w3.org
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

- a clockmodule. one custom js node

- 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:


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?

Received on Thursday, 2 August 2012 20:35:54 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Thursday, 2 August 2012 20:35:54 GMT