[CLAM] synthesizing SMS models in Pd

Xavier Amatriain xavier at amatriain.net
Fri Dec 14 14:21:18 PST 2007

Hi Rich,

As Richard said the 1SFT data is ready to go into the IFFT. A different 
story is what you need to do afterwards to
get a smooth synthesized sound. I am not sure what *window* you are 
talking about because there are two involved in the
process. The analysis window, which by default is a BlackmanHarris92 
with a 75% overlap. You need to multiply by the
inverse of this window after the SFFT. And then a completely independent 
triangular window with a size equal to twice
the analysis hop and overlap 50%. This is the one in charge of getting a 
smooth overlap and add process in place.

Hope it helps.


Rich E wrote:
> Okay, I didn't think of looking for the overlap size by checking the 
> timestamps, but that seems obvious now.. thanks!  I have found there 
> are many things preventing the SDIF files from being used in real-time 
> (such as the 1TRC frames not containing birth and death information).  
> So I am already buffering the data in a format that can be used in 
> real-time, so finding the overlap before sysnthesis-time shouldn't be 
> a problem.
> However, I do not see the 1WIN matrix within the SMS-produced files.  
> I assumed it is a triangle window with an overlap factor of 2 (this is 
> the default settings in SMSTools), but of course this can be changed, 
> in which case I would not know how to find the windowing function.  
> But I tried these settings without success (in comparison to 
> SMSTools-produced residual sound), so I am still looking for the 
> correct ones.
> cheers,
> rich
> On Dec 14, 2007 6:30 PM, Richard Dobson 
> <richarddobson at blueyonder.co.uk 
> <mailto:richarddobson at blueyonder.co.uk>> wrote:
>     Rich E wrote:
>     > Okay, sorry for getting into too much pd stuff... I basically just
>     > need to know what needs to be done to the 1STF data before I can
>     > synthesize it.  Is it ready to go, or is windowing still necessary?
>     > Should the frames be overlapped?
>     >
>     It's plain real/imaginary DFT data. SO in that sense yes it is
>     ready to
>     go straight into the IFFT. It will almost certainly require windowing.
>     If you haven't already done so, you will neded to check the formal
>     definition of the 1STF format e.g. at:
>     http://www.cnmat.berkeley.edu/SDIF/FrameTypes.html#1STF
>     SDIF is famous/notorious for being particularly "loose" about
>     definitions and content. In short, each frame (matrix) is time-stamped
>     (from the centre of the window, because they like doing things that
>     way), and you have to determine the overlap from that (which means you
>     have to read at least two frames before you can start rendering,
>     so this
>     is not  a true real-time streaming format; one would assume the
>     overlap
>     is constant, but the format does not see the need to mandate it);
>     there
>     should be a 1WIN matrix that defines the window to use. Beyond
>     that, all
>     I can say is "good luck"!
>     Richard Dobson
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