Re: [Libxtract-devel] libxtract, SC UGens and FFT

[Jamie B. <ja...@po...>]

On Fri, 2007-03-16 at 16:56 +0000, Dan Stowell wrote:

> A couple more MFCC questions, hope you don't mind:
> 
> Windowing: the xtract_mfcc method takes time-domain data in but doesn't 
> seem to do any windowing, so I guess the windowing is expected to be 
> handled before the data reaches libxtract. Is that right? It's possible 
> that the filters somehow have the windowing implicit, but I'm guessing not.
> 

Actually there was an error in the docs which I have now fixed. For
xtract_mfcc() *data should point to an array of spectral magnitudes. The
assumption throughout libxtract is that windowing and/or pre-filtering
will be done by some external function.

> Alloc'ing: I can see in the PD example how you're allocating memory for 
> the mel filter, assuming "getbytes" is a PD realtime-malloc-type-thing. 
> (Is t_float something PD-specific, or just the same as float?)
> 

It's just a float, included (I think) for portability reasons.

> One thing that I'm wondering about is the malloc in the xtract_mfcc() 
> method. I'm not sure why you malloc some new space to copy the data into 
> - you don't seem to do anything there except read the data. Would it be 
> safe to get rid of that malloc/memcpy/free? It might be a hangover from 
> an older way of doing things.
> 

Yes, I think it's a hangover. I've removed it.

> Similarly there's a malloc in the DCT routine, not sure why that's 
> needed. Maybe there's a reason for these that I've missed (thread safety?).
> 

I've removed that too. I've haven't even started considering things like
thread safety yet.

best,

Jamie