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Fozzie
Joined: Jun 04, 2004
Posts: 875
Location: Near Wageningen, the Netherlands
Audio files: 8
G2 patch files: 49
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ian-s
Joined: Apr 01, 2004
Posts: 2672
Location: Auckland, New Zealand
Audio files: 42
G2 patch files: 626
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 Posted: Thu May 10, 2007 2:33 pm Post subject:
Re: Anti-aliased osc effect? |
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| Fozzie wrote: | | it could be an anti-aliasing thing. Correct? |
Yes, it looks like a windowed sinc. As used in MinBLEP |
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Tim Kleinert
Joined: Mar 12, 2004
Posts: 1148
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236
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| Posted: Sun May 13, 2007 2:37 am Post subject:
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The flank of the sawtooth oscillator is not a 100% perfect flank. A perfect flank is most susceptible to the jitter caused by the sampling frequency of the system, which therefore, at higher oscillation frequencies, will produce aliasing artefacts and render the oscillation not useful as a tone source.
The waveform is therefore treated by a process called bandlimited interpolation, which rounds off those flanks just enough to make them immune to sampling frequency jitter. The same happens (doubly) with pulse wave oscillators. You'll notice that the higher you sweep pulse waves on a digital synth which sports good anti-aliasing, the more they will start to look like simple sine waves, as the bandlimiting flank will take up more and more of the waveform cycle.
Normally all of this goes unnoticed. But in cases like yours, it manifests. Other examples are deriving a pulse wave from a sawtooth wave via a comparator (the resulting pulse wave will be jittered), or deriving a triangle waveform from the sawtooth via a rectifier (the resulting triangle wave will be slightly jagged on one of its edges).
The sawtooth LFO however has a perfect flank, as it is not intended to be a tone source. Hence, sweeping the phase osc through 0-360 degrees with a sawtooth LFO will not produce any discontinuities. |
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Tim Kleinert
Joined: Mar 12, 2004
Posts: 1148
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236
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| Posted: Sun May 13, 2007 2:45 am Post subject:
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BTW, what's that oscilloscope software you are using? Can one use it in tandem with the demo software? If so, I want to have that.  |
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Tim Kleinert
Joined: Mar 12, 2004
Posts: 1148
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236
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Fozzie
Joined: Jun 04, 2004
Posts: 875
Location: Near Wageningen, the Netherlands
Audio files: 8
G2 patch files: 49
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| Posted: Sun May 13, 2007 3:30 am Post subject:
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| tim wrote: | | BTW, what's that oscilloscope software you are using? Can one use it in tandem with the demo software? If so, I want to have that. |
Yes, you can use it in tandem with the demo; no cables necessary, it can monitor the output of your soundcard(the output drivers I guess), I use it with my laptop built-in low quality soundcard without problems. It is visual analyser 8, available as free- or donationware at http://www.sillanumsoft.com. I noticed that v9 is now available, but have no idea what has changed. It is a very nice way to directly monitor what is going on!!
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Tim Kleinert
Joined: Mar 12, 2004
Posts: 1148
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236
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| Posted: Sun May 13, 2007 3:39 am Post subject:
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| Very practical, thanks! |
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Fozzie
Joined: Jun 04, 2004
Posts: 875
Location: Near Wageningen, the Netherlands
Audio files: 8
G2 patch files: 49
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| Posted: Sun May 13, 2007 4:25 am Post subject:
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| tim wrote: | | Just for fun -here's an non-bandlimited DIY sawtooth oscillator. Compared to the saw LFO, it has the advantage of audiorate (96kHz) processing. It doesn't sound that bad actually. However, the exponential tracking isn't 100% accurate (due to math precision of the LevelScaler module), but still usable. |
Thanks for your patch and sharing of knowledge! I'll study it and see if it is usefull for what I was trying to do (was looking into synced sinewaves because of the hammond thread here).
.... Ok, forgot posting this message and played around with it. You are really good in scaling signals! Nice mechanism; how dis you figure out the (mixer/levelscaler) settings, is it trial & error or is it calculated somehow?
(edit: BTW, using a bit of keyboard morph on the fine tune helps to even the tuning out a bit, although it then varies per note. Nothing noone could figure out for themselves, but I thought I'd just post it)
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Tim Kleinert
Joined: Mar 12, 2004
Posts: 1148
Location: Zürich, Switzerland
Audio files: 7
G2 patch files: 236
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| Posted: Sun May 13, 2007 3:29 pm Post subject:
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| Fozzie wrote: | | .... Ok, forgot posting this message and played around with it. You are really good in scaling signals! Nice mechanism; how dis you figure out the (mixer/levelscaler) settings, is it trial & error or is it calculated somehow? |
Both, actually. I use the LevelScaler for the linear-to-exponential conversion, so that the sawtooth circuit tracks the chromatic scale. The same technique is used to tune delay lines to make physical models.
The levels on the 4-channel-mixer within the oscillation-generating feedback loop are then tuned by ear.
BTW: I hope you downloaded the last&final version of the sawtooth circuit, because I uploaded several versions of it (always finding a better way to patch it a few minutes after uploading -sorry 'bout that).
| Fozzie wrote: | | (edit: BTW, using a bit of keyboard morph on the fine tune helps to even the tuning out a bit, although it then varies per note. Nothing noone could figure out for themselves, but I thought I'd just post it) |
Oh, great, I'll try that. |
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