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PostPosted: Tue Apr 11, 2017 3:44 pm 
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Joined: Tue Apr 11, 2017 10:44 am
Posts: 3
I want to know if this is how the time epoch box works in the spaceship scenario . and I have 2 questions :

1 . how does the time epoching work in conjunction with the average box ? after bandpassing the input stream we have a time epoching box which I think works like this (assuming we epoch duration is 0.3 sec and epoch interval is 0.1 sec and assuming that xi is a vector):

time(msec) : 1 2 3 4 5 6

input : x1 x2 x3 x4 x5 x6

output : x1 x2 x3 x2 x3 x4 ...

now assume we give this output to the average box.

it's documentation says :

"This plugin computes the average of each incoming sample buffer and outputs the resulting signal."

"The output signal's sample count per channel per buffer is one, since a buffer contains the averages (per channel) of the values of an input buffer. "

so by epoching the signal we have increased the buffer size ? and now the average is computed over 3 vectors rather than 1 ?

also the output of the average would be the average of vectors x1 , x2 ,x3 from 0.1 to 0.2 then average of x2,x3,x4 from 0.2 to 0.3 ? is this correct ?


2. in the spaceship scenario is it necessary to epoch the signal before giving it to the DSP box with the formula "x*x" ?
as I understand "x*x" just squares the elements of the vectors in our stream . so epoching should not have an effect on it .

p.s sorry if my questions are naive !


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PostPosted: Fri May 05, 2017 7:26 am 
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Joined: Tue Dec 04, 2012 3:53 pm
Posts: 536
Location: INRIA Rennes, FRANCE
Hi Kiyarash,

without going into the details, if you ask epoch of 5 seconds, one buffer will contain 5 seconds worth of samples. You can imagine a sliding window of that size taking snapshots of the data with the window 'stepping forward' by the amount of time specified by the interval. The output of the box are these 'snapshots'.

The average is computed from whatever samples are in each received buffer.

Finally, although you can use simple dsp at any point, there can be a difference between E[xx] and E[x]E[x]: you need to decide if you average squares or square averages.


Cheers,
Jussi


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