How-to-use-sound-functions

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Date: Sun 12-Dec-1991 11:55:38 
From: arun@ac.dal.ca
Subject: How to use sound functions

Here is a simple little routine to less you process sound files.
It is really quite fun to experiment with.
It is currently set up to make a weird kind of echo.
For a high pass filter try:
(in the function Process at the end)
for (i=1; i<numSamples; i++) {
  outSamples[i]=inSamples[i]-inSamples[i-1];
}
For a low pass filter try:
  outSamples[i]=(inSamples[i]+inSamples[i+1])>>1;
Have fun...
-George (using friends account)
respond to:
george@[129.173.30.20]
#include <stdio.h>
#include <sound/sound.h>
#include <math.h>

/* Sound error handling macro */
#define	soundErrorExit() {\
            fprintf(stderr, "%s: sound error: %s\n", programName, \
	        SNDSoundError(soundError)); \
	    exit(1); \
        }

static void	transform(SNDSoundStruct **outputSound,
		    SNDSoundStruct *inputSound);
static void	Process(short *outSamples, short *inSamples, int numSamples);

static int	soundError;	/* used by soundErrorExit() macro */
static char	*programName;

main(int argc, char *argv[])
{
    SNDSoundStruct	*inputSound, *outputSound;
    char		*inputSoundFile, *outputSoundFile;

    /* Check arguments */
    programName = argv[0];
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <inputSoundFile> <outputSoundFile>\n",
	        programName);
	exit(1);
    }
    inputSoundFile  = argv[1];
    outputSoundFile = argv[2];
    	
    /* Read sound file */
    if (soundError = SNDReadSoundfile(inputSoundFile, &inputSound))
	soundErrorExit();
    
    /* Transform sound */
    transform(&outputSound, inputSound);

    /* Write sound file */
    if (soundError = SNDWriteSoundfile(outputSoundFile, outputSound))
	soundErrorExit();
}


/* Transform inputSound and place result in outputSound */
static void	transform(SNDSoundStruct **outputSound,
		    SNDSoundStruct *inputSound)
{
    int		size     = inputSound->dataSize;
    int		format   = inputSound->dataFormat;
    int		rate 	 = inputSound->samplingRate;
    int		channels = inputSound->channelCount;
    short 	*inPtr;
    short 	*outPtr;

	printf("size = %d format = %d rate = %d channels = %d \n",
                           size, format, rate, channels);
    /* Abort if unsupported format */
    if (format != SND_FORMAT_LINEAR_16) {
        fprintf(stderr, "%s: unsupported sound format: %d\n",
	    programName, format);
	exit(1);
    }
    
    /* Allocate a new sound */
    if (soundError = SNDAlloc(outputSound, size, format, rate, channels, 4))
	soundErrorExit();

    /* Process input sound an write to output sound */
    inPtr  = (short *) ((char *) inputSound   + inputSound->dataLocation);
    outPtr = (short *) ((char *) *outputSound + (*outputSound)->dataLocation);
    Process(outPtr, inPtr, size / 2);
}


/* Process the sound any way you want to */
static void	Process(short *outSamples, short *inSamples, int numSamples)
{
 int i, echo, r1, r2;
 for (echo=1; echo<4; echo++) {
 r1=random()&0x7f00;
 r2=random()&0x7f00;
 for (i=0x7f00; i<numSamples; i+=2) {
   inSamples[i] = (inSamples[i]+inSamples[i-r1]>>1)*.75;
   inSamples[i+1] = (inSamples[i+1]-inSamples[i+1-r2]>>1)*.75;
 }
 }
 for (i=0; i<numSamples; i++) {
   outSamples[i]=inSamples[i];
 }
}
These are the contents of the former NiCE NeXT User Group NeXTSTEP/OpenStep software archive, currently hosted by Marcel Waldvogel and Netfuture.ch.