Algorithm 3.2 is a C++ program analogous to the MATLAB program for generating scales. It uses the same functions for writing to the sound device as used the last section of Chapter 2. You can try your hand at a similar program by doing one of the suggested programming exercises. The first exercise has you generate (or recognize) chords of seven types in different keys. The second exercise has you generate equal tempered and just tempered scales and listen to the result to see if your ears can detect the small differences in frequencies. Both of these programs can be done in either MATLAB or C++.
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//This program works under the OSS library
#include <sys/ioctl.h> //for ioctl()
#include <math.h> //sin(), floor()
#include <stdio.h> //perror
#include <fcntl.h> //open, O_WRONLY
#include <linux/soundcard.h> //SOUND_PCM*
#include <iostream>
#include <stdlib.h>
using namespace std;
#define LENGTH 1 //number of seconds
#define RATE 44100 //sampling rate
#define SIZE sizeof(short) //size of sample, in bytes
#define CHANNELS 1 // number of stereo channels
#define PI 3.14159
#define SAMPLE_MAX 32767 // should this end in 8?
#define MIDDLE_C 262
#define SEMITONE 1.05946
enum types {BACK = 0, MAJOR, MINOR};
double getFreq(int index){
return MIDDLE_C * pow(SEMITONE, index-1);
}
int getInput(){
char c;
string str;
int i;
while ((c = getchar()) != '\n' && c != EOF)
str += c;
for (i = 0; i < str.length(); ++i)
str.at(i) = tolower(str.at(i));
if (c == EOF || str == "quit")
exit(0);
return atoi(str.c_str());
}
int getIndex()
{
int input;
cout
<< "Choose one of the following:\n"
<< "\t1) C\n"
<< "\t2) C sharp/D flat\n"
<< "\t3) D\n"
<< "\t4) D sharp/E flat\n"
<< "\t5) E\n"
<< "\t6) F\n"
<< "\t7) F sharp/G flat\n"
<< "\t8) G\n"
<< "\t9) G sharp/A flat\n"
<< "\t10) A\n"
<< "\t11) A sharp/B flat\n"
<< "\t12) B\n"
<< "\tor type quit to quit\n";
input = getInput();
if (! (input >= BACK && input <= 12))
return -1;
return input;
}
void writeToSoundDevice(short buf[], int buffSize, int deviceID) {
int status;
status = write(deviceID, buf, buffSize);
if (status != buffSize)
perror("Wrote wrong number of bytes\n");
status = ioctl(deviceID, SOUND_PCM_SYNC, 0);
if (status == -1)
perror("SOUND_PCM_SYNC failed\n");
}
int getScaleType(){
int input;
cout
<< "Choose one of the following:\n"
<< "\t" << MAJOR << ") for major\n"
<< "\t" << MINOR << ") for minor\n"
<< "\t" << BACK << ") to back up\n"
<< "\tor type quit to quit\n";
input = getInput();
return input;
}
void playScale(int deviceID){
int arraySize, note, steps, index, scaleType;
int break1; // only one half step to here
int break2; // only one half step to here
int t, off;
double f;
short *buf;
arraySize = 8 * LENGTH * RATE * CHANNELS;
buf = new short[arraySize];
while ((index = getIndex()) < 0)
cout << "Input out of bounds. Please try again.\n";
f = getFreq(index);
while ((scaleType = getScaleType()) < 0)
cout << "Input out of bounds. Please try again.\n";
switch (scaleType) {
case MAJOR :
break1 = 3;
break2 = 7;
break;
case MINOR :
break1 = 2;
break2 = 5;
break;
case BACK :
return;
default :
playScale(deviceID);
}
arraySize = LENGTH * RATE * CHANNELS;
for (note = off = 0; note < 8; ++note, off += t) {
if (note == 0)
steps = 0;
else if (note == break1 || note == break2)
steps = 1;
else steps = 2;
f *= pow(SEMITONE, steps);
for (t = 0; t < arraySize; ++t)
buf[t + off] = floor(SAMPLE_MAX*sin(2*PI*f*t/RATE));
}
arraySize = 8 * LENGTH * RATE * SIZE * CHANNELS;
writeToSoundDevice(buf, arraySize, deviceID);
delete buf;
return;
}
int main(){
int deviceID, arg, status, index;
deviceID = open("/dev/dsp", O_WRONLY, 0);
if (deviceID < 0)
perror("Opening /dev/dsp failed\n");
arg = SIZE * 8;
status = ioctl(deviceID, SOUND_PCM_WRITE_BITS, &arg);
if (status == -1)
perror("Unable to set sample size\n");
arg = CHANNELS;
status = ioctl(deviceID, SOUND_PCM_WRITE_CHANNELS, &arg);
if (status == -1)
perror("Unable to set number of channels\n");
arg = RATE;
status = ioctl(deviceID, SOUND_PCM_WRITE_RATE, &arg);
if (status == -1)
perror("Unable to set sampling rate\n");
while (true)
playScale(deviceID);
}
Algorithm 3.2