On Wed, 6 Jan 2010 05:31:15 -0800 (PST), amcneilly
<amcneilly@gmail.com> wrote:

>I have the following query in relation to Cross-correlation and
>general Audio DSP
>
>signalA is 512 samples @ 44100 samples/sec. length 0.0116 seconds
>
>I take a recording and play signalA at 0.5 seconds. The recording is 1
>second long or 44100 samples @ 44100 samples/sec.
>
   [Snipped by Lyons]

Hi amcneilly, 
    your post seems confusing the me.  You have 
an "signalA" signal, 0.0116 seconds in length.  What 
do "take a recording" and  "play signalA at 0.5 
seconds" mean?  What "recording" is one second long?
What does the word "recording" mean?

[-Rick-]

On Wed, 6 Jan 2010 05:31:15 -0800 (PST), amcneilly <amcneilly@gmail.com> wrote:
> I have the following query in relation to Cross-correlation and
> general Audio DSP
> 
> signalA is 512 samples @ 44100 samples/sec. length 0.0116 seconds
> 
> I take a recording and play signalA at 0.5 seconds. The recording is 1
> second long or 44100 samples @ 44100 samples/sec.
> 
> When i do a Cross-correlation of signalA and the recording. i plot the
> result in MatLab and i get the result i was expecting.
> 
> My query is the unexpected result i get when i attempt to shrink the
> recording. I know that the chirp is produced at 0.5 seconds so i take
> a clip of the recording from (0.5 - 0.6) seconds and then do a Cross-
> correlation of signalA and the clip of the recording of 0.1 seconds or
> 4410 samples in length. the result of the plot of the Cross-
> correlation is a modified horizontally compressed version of my
> orignal plot. I was not expecting this. i was expecting the peak
> section form my orignal plot.
> 
> Why am i receiving this result?

amcneilly,

I'm not a DSP expert, nor do I play one on TV (Sigh!), but I'll
risk exposing my ignorance.

First, you mention "the chirp" in passing, but offer no real
description of the signal you are working with. You might consider
adding this on your next post.

Second, If I had a signal that looked like the following (using 0-9
to represent amplitude):

A:       000000012598877766655555444433322210000000000000000000000

and I cross-correlated it with itself, I'd expect this:

AxA:     000000000090000000000000000000000000000000000000000000000

(Hey, it's a simulation, so it always works perfectly and has no
 noise! <grin!>)

If I correlated this segment "Clip"

Clip:    988777666555554444

with A I'd expect it to match up in the same location:

A:       000000012598877766655555444433322210000000000000000000000
Clip:              988777666555554444
AxClip:  000000000090000000000000000000000000000000000000000000000

Maybe I missed something, What did your AxA look like, and did you
expect AxClip to look like?

Or did I miss something (alwasy possible)?


Frank McKenney
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I have the following query in relation to Cross-correlation and
general Audio DSP

signalA is 512 samples @ 44100 samples/sec. length 0.0116 seconds

I take a recording and play signalA at 0.5 seconds. The recording is 1
second long or 44100 samples @ 44100 samples/sec.

When i do a Cross-correlation of signalA and the recording. i plot the
result in MatLab and i get the result i was expecting.

My query is the unexpected result i get when i attempt to shrink the
recording. I know that the chirp is produced at 0.5 seconds so i take
a clip of the recording from (0.5 - 0.6) seconds and then do a Cross-
correlation of signalA and the clip of the recording of 0.1 seconds or
4410 samples in length. the result of the plot of the Cross-
correlation is a modified horizontally compressed version of my
orignal plot. I was not expecting this. i was expecting the peak
section form my orignal plot.

Why am i receiving this result?