From: Jim Peters (jim_at_uazu.net)
Date: 2002-03-13 22:34:48
Dave wrote:
> Jim-P -- what were your reaons for wanting to store 32-bit floating
> point sample data again as opposed to 16-bit integers?
At one point someone (Joerg or Andreas) mentioned using some kind of
24-bit convertor. (I can't remember the details -- I think it could
shift in different ranges). Also, recently, Andreas mentioned
something where you might be able to extract 18 bits of data. If
there is a chance that we might have a greater number of bits than 16,
then we might as well plan for it if we're defining a format.
> What do you think of their "hack" to store floating point
> (http://www.hsr.nl/bobkemp/edf/edffloat.htm) in the EDF file? Is
> that the only remaining obstacle to using the EDF format for us?
I would rather not use that log-scale floating-point stuff of theirs
for 24-bit data, say, because it would be a lot better just to make up
another new hack for EDF and store it that way, without any loss of
accuracy -- for example we could take pairs of 2-byte words and put a
32-bit float in there.
I know Sar wants to use EDF for his project, probably for
compatibility with EDF software, but I'm not sure about using it as a
standard format of the OpenEEG project -- that is, if we're going to
have a standard format.
Everything in EDF has a fixed size. Even if you use annotations, you
have to work out before you start writing the file roughty how much
you think you might write, because once you've started you can't give
yourself any extra space. I guess we could use it if people really
want to.
Really EDF is like all those old DOS databases with fixed length
fields. If you've got too much to write, then you are out of luck.
We could do something better than that. (Like my two-file idea:
binary file + descriptive file).
Alternatively, we could forget trying to do something better, and just
join the EDF party ...
I don't know -- I've already suggested a binary file format. I could
do another version of that with the ranges and tag-key in there, and
call that "Jim's proposed binary format", and leave it at that, with
people free to use it or ignore it.
I could even propose a format for the other file, although that might
take a little more work.
I don't know ...
Jim
-- Jim Peters (_)/=\~/_(_) jim_at_uazu.net (_) /=\ ~/_ (_) Uazú (_) /=\ ~/_ (_) http:// B'ham, UK (_) ____ /=\ ____ ~/_ ____ (_) uazu.net
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