[Numpy-discussion] Re: 24bit arrays

[Ray S. <ra...@bl...>]

>Is there some clever way to achieve the same goal for 24bit data without
>copying  everything into a new 32-bit array?

I agree with the other post, Int8 x 3 can be used with slices to get a lot done, depending on data tasks desired, but not all

>The typical 24bit audio file contains two interleaved channels, i.e.
>frames of 3bytes+3bytes, so it can be cast to (nframes,3) Int32, or
>(nframes,2,3) Int8 array, but this is hardly a useful representation for
>audio data.

Along these liners, I have been working with 24 bit ADC  data returned from pyUSB as tuples, which I need to convert to Float32 and save, like this:
WRAP = 2.**23
BITS24 = 2.**24

            try:
                chValue = struct.unpack(">I", 
                                  struct.pack(">4b", 0,*dataTuple[byteN:byteN+3])
                                )[0]
            except:
                chValue = 0
            if chValue>WRAP:
                chValue = ((BITS24-chValue) / WRAP) * gainFactors[thisCh]
            else:
                chValue = (-chValue / WRAP) * gainFactors[thisCh]
            data[thisCh].append(chValue)

which is really slow (no real time is possible).
Is there a much faster way evident to others here? 
We are going to do a pyd in C otherwise...

Ray