# Re: [sc-users] trying to understand multichannel expansion

```Fredrik Olofsson wrote:
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```25 dec 2009 kl. 17.45 skrev Jonatan Liljedahl:

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```James Harkins wrote:
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```On Dec 25, 2009, at 8:54 AM, Jonatan Liljedahl wrote:
```
First, it seems that an array inside a toplevel array does not expand but is mixed instead, but I can't find any note about this in the docs about multichannel expansion. example:
```
{SinOsc.ar([[100,120],[105,125]],0,0.2)}.play

```
The left channel is the sum of two sines with 100 and 120 hz, the right 105 and 125...
Yes, but this is purely accidental. This actually creates a pair of subgraphs in the same SynthDef, and they both write to the same output bus. The summation happens when the signals are added into the bus. Illustrated here by Rohan Drape's brilliant "dot" extension:
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Cool, I've been thinking of making a graphviz-dot extension myself, and am happy to hear that it already exists! :) Where can I find it? Google just brings me an old email with a dead link.
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it's available as a quark these days (rd_dot - see Quarks helpfile on how to install, or http://quarks.svn.sourceforge.net/viewvc/quarks/rd_dot/). also i think it still lives here... http://www.slavepianos.org/rd/?t=sc3-dot rohan has more nice sc related software there... http://www.slavepianos.org/rd/
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Thank you fredrik, I found it. I've tried it out a bit and it's really helpful when trying to figure out synthdefs.
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When you provide a one-dimensional array to Out, the array items are placed on sequential buses (0, 1 etc.). A two-dimensional array causes Out to multichannel expand, writing multiple signals on each of the consecutive buses. There is NO collapsing of the signals into simpler arrays before Out -- therefore, any operation you do on the multidimensional array will occur for every individual item.
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Ok, I see! Thanks for clearing this up. Maybe this should be mentioned in the multichannel expansion helpfile?
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/Jonatan
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```

#|
fredrikolofsson.com     klippav.org     musicalfieldsforever.com
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