How can I use preprocessor standalone with a wav file?

I have been tyring to use the preprocessor standalone by feeding it pcm data from a headerless pcm file (mono, 22050hz) 
and then write the result to another file. Unfortunately, all I get back is noise (first frame is set to 0, rest is noise). 
Frame size is set to 440. 

I just modified testdenoise.c slightly to read/write from a file (see below) but I can't get useful results. What am I doing wrong? Do I need to perform additional initializations? 

I am using 1.2rc1, target platform is windows (using Visual Studio).

Thank you for your help. 

-----------------   Modified version of testdenoise.c   ----------------------

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <speex/speex_preprocess.h>
#include <stdio.h>

#define NN 440

int main()
{
   short in[NN];
   int i;
   SpeexPreprocessState *st;
   int count=0;
   float f;

   char *inFile = "C:\\Temp\\in.wav"; //.wav file containing only pcm data, no header info
   int close_in=0;
   char *outFile= "C:\\Temp\\out.wav"; 
   FILE *fin, *fout=NULL;

   fin = fopen(inFile, "rb");
      if (!fin)
      {
         perror(inFile);
         exit(1);
      }
   close_in=1;

   fout = fopen(outFile, "wb");
   if (!fout)
   {
      perror(outFile);
	  if (close_in == 1)
		  fclose(fin);
      exit(1);
   }

   st = speex_preprocess_state_init(NN, 22050);
   
   i=1;
   speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_AGC, &i);   //enabling AGC; denoise is enabled by default
   i=8000;
   speex_preprocess_ctl(st, SPEEX_PREPROCESS_SET_AGC_LEVEL, &i);   

   while (1)
   {
      int vad;
      fread(in, sizeof(short), NN, fin);
      if (feof(fin)) 
         break;
      vad = speex_preprocess_run(st, in);
       fwrite(in, sizeof(short), NN, fout);
      count++;
   }
   speex_preprocess_state_destroy(st);

   fclose(fin);
   fclose(fout);

   return 0;
}

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