[PD-ot] Re: [PD] smallest possible value of a delay-time

pix pix at test.at
Fri May 14 00:59:20 CEST 2004


hmm, quickly thinking about it (and moving the discussion to the [OT]
list)...

since you can't actually generate output out of sample boundaries, even
though you might be able to interpolate and find out a delay value less
than one sample, you will only be about to output it during the next
sample. but latency is always going to be much more than one sample
anyhow, so i guess i can assume you don't care about this.

the other thing is that you only have two samples to play with, the
current sample and the last sample. so the best you can do is linearly
interpolate, which doesn't sound so great. (well you theoretically have
access to all of the previous samples, but normally to do interpolation
you need points symetrically before and after the point you want to
interpolate).

if C is the current sample and L is the previous sample, you could
linearly interpolate between them with something like C*t+L*(1-t). where
t is between 0,1 and is the fractional number of samples you want to
delay. you can get L in pd using the zexy "z" object.

if you are less concerned about realtime, you could keep a buffer of the
last few input samples and do better interpolation. your final output
will be delayed, but the relative delay between your input signal and
your interpolated delay will be less than one sample.

btw, i'm no academic, don't go using this as gospel to shout down your
teacher. but feel free to use it as inspiration ;)

pix.

On Fri, May 14, 2004 at 12:35:17AM +0200, Roman Haefeli wrote:
> hi
> 
> i had a discussion with a teacher today. the topic was the smallest
> delay-time possible. in his opinion one sample is the atom of signal and
> cannot be divided anymore. in my opinion it should be possible to get
> shorter delays than 1 samples with interpolation. my argument was: it should
> be possible to set the values of each sample so, that the resulting signal
> would be similar to a digitized analogue signal with a shorter than 1 sample
> delay.
> 
> Does anybody know a good explanation for this problem?
> 
> i konw, this haven't got anything to do with pd. but i think you are the
> right people to ask. by the way: if it is possible, how would a realization
> in pd look like?
> 
> thank you for helpin me
> 
> roman
> 
> 
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