On 2 Feb, 00:37, Jessica <pt...@live.com> wrote:
> I am looking for an open-source smoother to down-sample data. I know
> there are many such as Hull Moving average, but I have data logged at
> the ms scale at non-fixed time intervals and I want to sample it on
> the second range at fixed time intervals. Does anyone know of a good
> smoother to do this? The key is that the input data is not logged at a
> constant frequency.

You need to decide why you want to do this, and what the end
purpose of the analysis is.

To give you an example what I mean, I have a project going
these days, where I monitor a sound source for hours at the
time. The recorder loggs data at 44 kHz for 12 hrs at the time.
The events I am looking for don't happen too often, but when
they do, they are a lot louder than the background noise.

The fist question is to get an overview of the data and see if
the events occur at all, and if so, in which file.

This can be done in a number of ways, including characterizing
the events and run a detector over the data to look for that
particular signature.

But that's not the only way.

To make quick sense of the data (12 hours worth of data
at CD quality is several GBytes of data), this is what I do:

- Make sure the recorder splits the data into manageable
sized files (64 MBytes)
- Load the data from file
- Split the data into second-long chunks
- Compute the energy of the data in each second-long chunk
- Store the vector of energy per second for each file
- Plot these vectors versus file.

If one does this correctly, the plot shows the background noise
level with the events I am looking for standing out as spikes
in the plot. From the plot I can easily identify exactly
which of the recorded files contain the event, and thus
find the exact data segment and go on with further analysis.

If you try and explain to yourself, your boss, or your
colleague, exactly what you want to obtain from whatever
procedure you are struggling with, you might find the clues
to the answer.

The only thing I can tell you right now is that resampling
a data set from the ms scale down to the minutes scale,
doesn't make much sense from the DSP point of view.

The constraints that govern DSP deal with downsampling
factors 2-10. You are talking about several thousands.

Rune