The windowed sinc filter generation code seems to be working fine. The FIR filtering code is also now working reasonably well. Occasionally the FIR filter will pop, but setting the normalization factor lower seems to help this. I suspect the problem is in the fixed point multiply/add. I also have a hunch the zero stuffing/sample discarding code is not correct, and I'll look at that soon to get it sorted out.

/*   SDLMain.m - main entry point for our Cocoa-ized SDL app
       Initial Version: Darrell Walisser <dwaliss1@purdue.edu>
       Non-NIB-Code & other changes: Max Horn <max@quendi.de>

    Feel free to customize this file to suit your needs
*/

#import <Cocoa/Cocoa.h>

@interface SDLMain : NSObject
@end