[PD] problem with switch~ and downsampling in 0.38-0test7

Matthias Blau blau_m at web.de
Mon Feb 21 21:51:30 CET 2005

In my opinion, the whole thing looks like switch~ sometimes does the 
switching in the upsampled (parent patch) domain although it sits in the 
subpatch, thereby generating high-frequency components at the interface 
between parent (upsampled) patch and subpatch.
In any case, if switch~ is used without downsampling, and the 
downsampling is then done in yet another subpatch using block~, then all 
problems disappear.
Thus, it appears that one should not use switch~ together with downsampling.

IOhannes m zmoelnig schrieb:
> Matthias Blau wrote:
>> Hi all,
>> Therefore I made a subpatch with [switch~ 64 1 0.5] which works most of 
> ...
>> Sometimes however, I get strong high frequency disturbances. I suspect 
>> a bug in switch, but maybe I am missing something?
> you might have problems with aliasing.
> the up/downsampling does very little (to no) pre-filtering.
> upsampling: depending on the argument the iolet~s will do linear 
> interpolation between 2 original samples at the best(!!!); this is not 
> very good; the default is zero-padding which is really awful (but is 
> there by intent, as you will very soon notice, that "something" is going 
> on)
> downsampling: if i remember correctly, it just takes every nth sample 
> (even if you specify "linear" there is no smoothing or whatever)
> so make sure that you filter your signal before/after down/upsampling.
> mfg.asd.r
> IOhannes
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