Very simple converter from list of frequencies and durations to output sound wave on stdout. Pipe it through e.g. /dev/audio or aplay to actually create sound.

point_of_no_return.sound

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sqsynth_v1.c

#include <math.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

const int freq = 8000; // aimed at 8kHz output
const int ampl = 255;

typedef struct LinkedList {
  uint64_t length;
  double frequ;
  struct LinkedList* next;
} LinkedList_t;

LinkedList_t* addNote(LinkedList_t* notelist, double duration, double pitch);
void playSound(LinkedList_t* sound);

int main(void) {
  double dur = 0.0, pitch = 0.0;
  LinkedList_t* baseList = NULL;
  LinkedList_t* curList = NULL;


  if(!(baseList = malloc(sizeof (LinkedList_t)))) {
    fprintf(stderr, "Unexpected memory error.  Maybe you're out of memory?\n");
    abort();
  }

  curList = baseList;

  while(1) {
    dur = 0.0, pitch = 0.0;

    scanf("%lf@%lf", &dur, &pitch);

    if(!feof(stdin)) {
      if(dur <= 0.0f || pitch < 0.0f || pitch > 20000.0f) {
	fprintf(stderr, "Invalid entry.  Please enter in the form duration@pitch.\n");
	while(fgetc(stdin) != '\n');
	continue;
      }
      
      if(curList = addNote(curList, dur, pitch))
	continue;
      else {
	fprintf(stderr, "Unexpected memory error.  Maybe you're out of memory?\n");
	abort();
      }
    } else {
      break;
    }
    
  }

  //When stdin is closed, play back music
  curList = baseList;

  while(curList != NULL) {
    LinkedList_t* prevList = NULL;
    playSound(curList);

    prevList = curList;
    curList = curList->next;
    free(prevList);
  }

}

LinkedList_t* addNote(LinkedList_t* list, double duration, double frequency) {
  if(list->next = malloc(sizeof (LinkedList_t))) {
    list->next->length = ceil(duration * freq);
    list->next->frequ = frequency;
  }
  return list->next;
}

void playSound(LinkedList_t* sound) {
  int i = 0;
  for(i = 0; i < sound->length; ++i) {
    int sample = signbit(sin(2.0*M_PI*sound->frequ*i/freq));
    
    putchar(sound->frequ == 0.0 ? 128 : 255 * sample);
  }
}