[SDL] Just can't get it done: resample sound

[William Petiot]

You should try to think about your problem in another way.. 
try to fill destination array _from_  the src array, not the opposite

this would be something like this : 

// WARNING : this code is untested, just written on the fly
// not optimized at all, certainly full of bugs
// btw: resampling without interpolation or filtering will sound weird :)

typedef unsigned long sample; // assuming 16 bits stereo

void resample(sample **ptr_dest,int *ptr_ndest, sample *src,int nsrc, float 
factor)
{
	int ndest,i ; 
	sample *dest;
	ndest = (int) (nsrc / factor); // new size
	dest = (sample *)malloc(ndest); 
	for (i = 0; i < ndest; ++i) {
		// filling all destination samples from source
		dest[i] = src[(int)(i*factor)]; 
		// note that we work in "sample" unit (1 sample is 4 bytes)
	}
	// filling caller parameters 
	*ptr_dest = dest;
	*ptr_ndest = ndest;
}

then, call this with :

	sample *my_sample;
	int my_sample_size;
	
	sample *my_resampled;
	int my_resampled_size;

	// code to fill my_sample, load from disk etc
	... 
	resample(&my_resampled,&my_resampled_size,my_sample,my_sample_size);
	...
	// use the sample
	... 
	free(my_resampled);

Hope it helps. This code is only for explanations, it's suboptimal. 

William.

On Saturday 03 April 2004 19:47, Johannes Bauer wrote:

> Hi folks,
>
> I posted here a while ago a message in which I asked for some help in
> resampling a sound sample in order to increase/decrease the pitch. I
> tried it back then and just couldn't get it done. Then I tried again
> right now and - once again - the result is all messed up. This is
> totally driving me nuts. Here's what I have:
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