GBDK 4-bit audio hex converter

/*

Raw unsigned 8-bit audio to 4bit audio for gameboy color

Audacity:

Mono track at 8192Hz project rate

(mono track)

Other uncompressed files -- RAW (header-less)
Unsigned 8 bit PCM

*/
Code seems to produce weird sounds on game boy advance running the dmg mode rom... not sure why

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

char * remove_ext(char * fn) {
	int c;
	for (c = 0; fn[c] != '.'; c++) {
		;
	}
	char * nfn = malloc(c * sizeof(char));
	for (c = 0; fn[c] != '.'; c++) {
		nfn[c] = fn[c];
	}
	nfn[c] = '\0';
	return nfn;

}

int main() {
	int k, file_size;
	long t;
	t = time(NULL); // seed rand
	srand(t);
	int nsamples = 0;
	char fn[50];
	int c;
	unsigned char hch0, hch1;
	FILE * f;
	unsigned char ch;
	while (1) {
		printf("\nFilename: \n");
		scanf("%s", fn);
		f = fopen(fn, "rb");
		if (f != NULL) {
			break;
		}
		else
		{
			printf("\n%s is not a valid file ?\n", fn);
		}
	}

	fseek(f, 0, SEEK_END); // seek to end of file
	file_size = ftell(f); // get filesize
	fseek(f, 0, SEEK_SET); // back to beginning of file

	char nfn_we[100];
	strcpy(nfn_we, remove_ext(fn));
	strncat(nfn_we, ".h", 2);
	//printf("\n%s\n", remove_ext(fn));
	//printf("%s", nfn_we); // for testing


	FILE * out = fopen(nfn_we, "wb");
	if (out == NULL) {
		printf("\nError creating new file.");
		return -1;
	}

	char definition[100];
	sprintf(definition, "\n#define SAMPLES %d\n\nconst UBYTE sample[] =\n{\n", file_size-1);
	fprintf(out, "%s", definition);
	for (c = 0; !feof(f); ch = fgetc(f), c++) {
		if (c % 2 == 0 && c > 0) {
				fprintf(out, "0x%02x,",  ((hch0 & 0b11110000) | ((hch1 & 0b11110000)) >> 4));
				nsamples++;

			}
		if (c % 2 == 0) {
			hch0 = ch;
		}
		if (c % 2 == 1) {
			hch1 = ch;
		}
		if (c % 24 == 0 && c > 0) {
			fprintf(out, "\n");
		}
	}

	fprintf(out, "\n");
	fputc('}', out);
	fputc(';', out);
	fclose(f);
	fclose(out);

	printf("\n%d samples\n", nsamples * 2);
	printf("\n%d filesize\n", file_size - 1);
	printf("\nPress any key...");
	getch();

	return 0;
}