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 Forum index » DIY Hardware and Software » ChucK programming language
Extreme level peak from SqrOsc oscillator
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ullyssen



Joined: Sep 22, 2017
Posts: 4
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PostPosted: Fri Sep 22, 2017 4:57 am    Post subject: Extreme level peak from SqrOsc oscillator Reply with quote  Mark this post and the followings unread

Hi!

I need some strange artifact to be removed from ChucK output.

I created the following code: simple function to control square oscillator:

Code:

fun void sqrG(int tone, int time, int silence)
  {
    SqrOsc o => ADSR e => dac;
    tone => o.freq;
    e.set(0::samp,2::samp,0.5,1::samp);      
    e.keyOn();
    time::ms => now;
    e.keyOff();
    silence::ms => now;
  }


Every time this function is executed, resulting square signal contains extreme level peak right at the beginning, as shown on this screenshot from Audition editor:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Interesting is that all other oscillator types (SinOsc, TriOsc, SawOsc) don't produce this artifact.
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g.gabba



Joined: Nov 29, 2008
Posts: 183
Location: berlin
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PostPosted: Fri Sep 22, 2017 8:17 am    Post subject: Reply with quote  Mark this post and the followings unread

hi,
what ur using to measure?
may a soundcard oszilloskope?
if so soundcards often have caps on there inputs that could provoke this behaviour on square waves.
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ullyssen



Joined: Sep 22, 2017
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PostPosted: Fri Sep 22, 2017 9:13 am    Post subject: Reply with quote  Mark this post and the followings unread

g.gabba wrote:
hi,
what ur using to measure?
may a soundcard oszilloskope?
if so soundcards often have caps on there inputs that could provoke this behaviour on square waves.


No, output was directly recorded to WAV file and analysed in Audtion CS6 editor.
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Blue Hell
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PostPosted: Fri Sep 22, 2017 9:20 am    Post subject: Reply with quote  Mark this post and the followings unread

It looks like the anti-aliasing behaves a bit strange directly after initialization ... it might be easiest to apply some startup envelope to mask the effect ...
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ullyssen



Joined: Sep 22, 2017
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PostPosted: Fri Sep 22, 2017 9:54 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
It looks like the anti-aliasing behaves a bit strange directly after initialization ... it might be easiest to apply some startup envelope to mask the effect ...


Could you provide me with some code example?
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Blue Hell
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PostPosted: Fri Sep 22, 2017 9:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, I'm not able to do so ... but I could interpret your image Laughing

Maybe Antimon can come up with something? (when he is not too busy preparing for two shows to run ...)

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ullyssen



Joined: Sep 22, 2017
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PostPosted: Fri Sep 22, 2017 1:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've changed the code, so

Code:
SqrOsc o => ADSR e => dac;


became


Code:
SqrOsc o => Dyno limiter1 => ADSR e => Dyno limiter2 => dac;


and then I've activated both limiter instances.
Yet this peak still emerges.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Mon Sep 25, 2017 3:09 am    Post subject: Reply with quote  Mark this post and the followings unread

What strikes me as strange is that ringing occurs BEFORE a step of the signal as well as AFTER the step.
Shocked

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Blue Hell
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PostPosted: Mon Sep 25, 2017 5:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Heh, ringing before means that it is not ringing but bandlimiting instead being in effect.
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Blue Hell
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PostPosted: Mon Sep 25, 2017 5:17 am    Post subject: Reply with quote  Mark this post and the followings unread

You can think of it being a square wave approximated by sines.
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