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 Forum index » Instruments and Equipment » Alesis Andromeda
A6 Sine and Tri voice idiosyncrasy?
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rh2y



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PostPosted: Sun Sep 07, 2008 3:01 pm    Post subject: A6 Sine and Tri voice idiosyncrasy? Reply with quote  Mark this post and the followings unread

Hi all...

I was just tinkering with my A6 a little this evening, working on a very basic patch. The patch has just the Sine and Tri oscillators enabled, with a basic envelope, one oscillator, nothing fancy.

Anyway, I was playing a bit while waiting for the synth to warm up, and I noticed that on two of the voices, the sound was a fair bit brighter than on the rest. I figured that, since I hadn't tuned yet, maybe two of the filter cutoffs were out of tune, making those two voices brighter.

I played for a while, until the unit was warmed up, then did an autotune, and surprisingly, it made no difference --- two of the voices are still noticeably brighter.

I *only* notice this if Sine and Tri (only) are selected. Not at all if only Tri is selected (and obviously, not if only Sine is selected).

Anybody else run into this? I'm wondering if it's the oscillators themselves; I guess the test there would be to open the filters all the way up and see if it's still noticeably brighter.

I'm running a second autotune right now, to see if that takes care of it, but I thought it was a bit odd.

Cheers,

Russ

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rh2y



Joined: May 08, 2007
Posts: 218
Location: Pittsburgh, USA
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PostPosted: Sun Sep 07, 2008 3:11 pm    Post subject: More on Sine & Tri waves... Reply with quote  Mark this post and the followings unread

I just re-ran auto-tune, and it still didn't fix it.

BUT, I thought about it a minute, and tried some other stuff; see if you all agree with my reasoning.

I turned the filters all the way open, so they wouldn't be factored into the brightness of the sound, so I could hear just the raw oscillators.

I was using a single oscillator, with Sine and Tri enabled. I suppose it's possible the the Sine oscillator and Tri oscillator may be two separate circuits, and on some of the voices, the phase of the Sine is slightly out of phase with the Tri, making the resultant waveform brighter or not.

I disabled OSC1, and turned on OSC2 on just Sine and Tri, and got the same effect, but in different voices.

If I use OSC1 and OSC2 together, and detune OSC2 a little from OSC1, you can't tell at all, and it sounds wonderful and joyous like an A6 should.

I guess it's just because I was using the most basic waveforms (Sine is hardly a great starting point in subtractive synthesis anyway, right? Smile ) that I was hearing this.

If somebody has a better theory, I'm all ears. I'm not *just* yet ready to believe there's something wrong with my A6, as it behaves as expected in every other aspect.

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LamerDeluxe



Joined: Jul 08, 2008
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PostPosted: Mon Sep 08, 2008 2:55 am    Post subject: Reply with quote  Mark this post and the followings unread

It could be that the sine wave is made by filtering a triangle wave. Filtering causes phase shift. And maybe the filtering components differ slightly between voices. Interesting find.
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rh2y



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PostPosted: Tue Sep 09, 2008 8:54 am    Post subject: Reply with quote  Mark this post and the followings unread

If I get some time later this week (yeah, that happens a lot), I may hook up my oscilloscope and see what the waveforms look like and post them here.
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Jyoti



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PostPosted: Tue Sep 09, 2008 8:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm... I shall have to try this myself! Good work! thumb up
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