[PD] reproduce envelope

[Roman Haefeli]

On Thu, 2008-10-30 at 17:32 +0100, Hans Roels wrote:
> Hello,
> 
> Is is possible in Pd to produce exactly the same envelope again and 
> again? If I send the same message to vline and use this to cut an 
> envelope out of noise or a sine wave, it always changes a bit (if you 
> listen carefully). (The phase is always reset, that's not the 
> problem.) I recorded the sounds, had a look at the soundfiles in an 
> edit program and noticed that all the envelopes were slightly 
> different. 

this is actually a feature of [vline~]. [vline~] understands scheduled
messages, which means, that messages triggered by [metro] or [delay] are
executed by [vline~] at the exact time of the [metro]/[delay] initiated
message. in other words: [vline~] starts ramps between audio blocks,
even between samples. the phase setting for [osc~] is only executed on
block boundaries. this is why you're getting inconsistent results with
[vline~] and [osc~]

> Then I used line~ in a subpatch with blocksize 1 and did 
> the same thing. This sounds better and if I looked at the recorded 
> sound files they were more identical (although the release changes a 
> bit, there seems to be a very small inaccuracy in the delay...


[line~] on the other hand is starting the ramp always on block
boundaries, that is why the phase reset and the ramp start at the same
time, which is giving you consistent results. different decays might be
the effect of rounding errors, since - in case you're not using  a
multiple of the block size as ramp length - the resulting ramp length is
sometimes rounded up and sometimes rounded off. (this is a only theory,
that needs to be confirmed by someone who knows to read the c code of
[line~]).

>  but 
> you can't hear this with the sine sound. The noise sound is always a 
> bit different, I guess because it are randomly generated frequencies?).

there is no phase reset for [noise~], so the results will always be
different. 

> Anyway I thought that vline~ was more precise than line~ but this 
> doesn't seem to be true...?

it is true, but many other objectclasses aren't. to mention only a few:

- right inlet of [osc~]  and [phasor~]
- [tabwrite~]
- [tabplay~]
- [writesf~]
- [readsf~]
probably more.

all those objectclasses execute incoming message only on
blockboundaries, which means, you get inconsistent results, when using
them together with the indeed more accurate [vline~].

roman



		
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