24-bit wav files and other observations

[Daniel J Sebald]

Dave, Paul,

I wanted to read a WAV file with 24 bit data width using auload()--rather than the 8, 16, or 32-bit facility.  I've made some simple changes (see attached patch), which brings up a few issues.


1)  The fread() routine always returns a variable of type 'double'.  You'd think that the variable would have the native format.  E.g.,

  data = fread(file, samples, 'uint8', 0, arch);

would mean 'data' to be of type 'uint8'.  I suppose it is a compatibility issue, and it isn't that big of deal.  In some instances it is a convenience, I suppose.  Other times not.


2)  Why does Octave/Matlab not have 'uint24' throughout?  For example, there'd be nothing unusual about

  data = fread(file, samples, 'int24', 0, arch);

and a type 'int24'.


3)  Dave, have I done this conversion as efficiently as possible?  Are there better ways of doing casting in the patch that are more direct?


4)  I tried implementing the behavior of the following line:

     data1 = data(1:3:end) + data(2:3:end) * 2^8 + cast(typecast(cast(data(3:3:end), 'uint8'), 'int8'), 'double') * 2^16;

as bit shifts in the following way:

     data = bitor(bitor(data(1:3:end), bitshift(data(2:3:end), 8)), bitshift(cast(typecast(cast(data(3:3:end), 'uint8'), 'int8'), 'double'), 16));

so I can double check for proper 24-bit construction.  However, this bit shift method doesn't work.  It comes down to the following quandary.  This looks correct:

octave:52> bitor(2, 1)
ans =  3

but when working with negative numbers, the following doesn't look correct:

octave:53> bitor(-2, 1)
ans =  1

I would think that bitor(-2,1) should be -1.  Is this a bug?


5)  Is the documentation for "who" correct?

-- Command: who options pattern ...
-- Command: whos options pattern ...
   List currently defined symbols matching the given patterns.  The
   following are valid options.  They may be shortened to one
   character but may not be combined.

  `-all'
        List all currently defined symbols.

  `-builtins'
        List built-in functions.  This includes all currently
        compiled function files, but does not include all function
        files that are in the search path.

  `-functions'
        List user-defined functions.

  `-long'
        Print a long listing including the type and dimensions of any
        symbols.  The symbols in the first column of output indicate
        whether it is possible to redefine the symbol, and whether it
        is possible for it to be cleared.

The options don't work.  I get:

octave:48> who x
Variables in the current scope:

x

octave:49> whos x
Variables in the current scope:

Attr Name         Size                     Bytes  Class
==== ====         ====                     =====  =====
     x      2209792x2                   35356672  double

Total is 4419584 elements using 35356672 bytes

octave:50> who -l x
warning: who: unrecognized option `-l'
Variables in the current scope:

x


Dan

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