I'm a beginner, and I try to make pitch goes up and down.
It seems simple, but I can't figure out.

Here is my code, and when I press key 'a', pitch goes up,
but when I press key 'b', pitch doesn't go down(still goes up). Anybody can help me please?

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import krister.Ess.*;

AudioChannel  myChannel4;

PitchShift myPitchShift;

int shift;

void setup() {
 size(200,500);
 

 Ess.start(this);

//  myChannel3=new AudioChannel("news.aif");
 myChannel4=new AudioChannel("yaa.aif");
//  myChannel3.play(Ess.FOREVER);

 myPitchShift=new PitchShift(Ess.calcShift(1));

 
 shift=5;
 
//  frameRate(30);

 stroke(255);
 fill(255);
}

void draw() {
 background(0,0,255);
//  rect(0,500-shift,256,shift);
 
 if (keyPressed==true) {
   if (key=='a'){
   myPitchShift.filter(myChannel4);  
   myChannel4.play();
   shift+=1;
 }
 if (key=='b'){
   myPitchShift.filter(myChannel4);
   myChannel4.play();
   shift=shift-1;
 }
}
}
public void stop() {
 Ess.stop();
 super.stop();
}