How to mute minim filter

Processing Libraries
4

Sure. Try moving the keyPressed code into a custom swap function. if your OSC signal is tested to true, then call the swap function.

import ddf.minim.*;
import ddf.minim.ugens.*; 
import ddf.minim.effects.*; 

Minim       minim;
AudioOutput out;
Oscil       wave;
BandPass    filt1;

float freq1;
float amp = .5;
int thresh = 8;
int fps = 60;

boolean bandOn;

void setup() {
  size(960, 540);
  frameRate(fps);
  background(0);
  rectMode(CENTER);

  minim = new Minim(this);
  out = minim.getLineOut();

  filt1 = new BandPass(440, 20, out.sampleRate());
  wave = new Oscil( 440, 0.5f, Waves.SQUARE );

  wave.patch(filt1).patch( out );
  bandOn = true;
}

void draw() {
  if (bandOn) {
    background (#64C6A6);
  } else {
    background (#C6A664);
  }

  boolean fakeOSCsignal = random(1.00)<0.01;
  if (fakeOSCsignal) {
    bandSwapper();
  }

  float passBand = map(mouseX, 0, width, 300, 2000);
  filt1.setFreq(passBand);
  float bandWidth = map(mouseY, 0, height, 300, 600);
  filt1.setBandWidth(bandWidth);

  float ellipseSize = height*.6;
  stroke(255);
  strokeWeight(4);
  float margin = 10;
  float waveAmp = 30;
  pushMatrix();
  translate(0, height/2);
  for (int i = 0; i < out.bufferSize() - 1; i++) {
    if (i> (width/2)-(ellipseSize/2)+margin && i< (width/2)+(ellipseSize/2)-margin) {
      line( i, - out.left.get(i)*waveAmp, i+1, - out.left.get(i+1)*waveAmp );
    }
  }
  popMatrix();
}

void bandSwapper() {
  if (bandOn) {
    filt1.unpatch(out);
    wave.unpatch(filt1);
    wave.patch(out);
    bandOn = false;
  } else {
    wave.unpatch(out);
    wave.patch(filt1);
    filt1.patch(out);
    bandOn = true;
  }
}