How can I clear/reset the canvas with a counter or countdown in Processing?

I would like to know how can I set a reset loop: While the draw() is going on I would like to clear the canvas so I can start to draw on a clean canvas again and again.

(I don't want to use keyPressed() or mousePressed() it has to be automatic)

import ddf.minim.*;
Minim minim;
AudioInput in;

void setup() {
  minim = new Minim(this);
  minim.debugOn ();
  in = minim.getLineIn(Minim.MONO, 100);
  fullScreen();
  background(255, 60, 80);
}

void draw() {
  float soundlevel;
  float distance_top = random(100);
  int t;
  int interval = 10;
  String time = "010";

  soundlevel = in.mix.get(0);

  stroke(255, random(90, 255));
  line(0, distance_top + soundlevel * 4000, width, distance_top + soundlevel * 1000);
  line(0, distance_top + soundlevel * 1000, width, distance_top + soundlevel * 4000);


  t = interval-int(millis()/100);
  time = nf(t, 3);
  if (t == 0) {
    redraw();
    interval = interval +10;
  }
}

Thank you for your help in advice!

You can simply clear the background again, for example when you press a key:

void keyPressed(){
  background(255, 60, 80);
}

You can do the same on some other event (amount of time, loudness, etc.)

Here's an example based on your code that clears the background every 3 seconds:

import ddf.minim.*;
Minim minim;
AudioInput in;

//3s as millis
int interval = 3 * 1000;
int time;

void setup() {
  fullScreen();
  background(255, 60, 80);

  time = millis();

  minim = new Minim(this);
  //minim.debugOn ();
  in = minim.getLineIn(Minim.MONO, 100);
}

void draw() {
  float soundlevel;
  float distance_top = random(100);

  soundlevel = in.mix.get(0);

  stroke(255, random(90, 255));
  line(0, distance_top + soundlevel * 4000, width, distance_top + soundlevel * 1000);
  line(0, distance_top + soundlevel * 1000, width, distance_top + soundlevel * 4000);

  if(millis() - time >= interval){
    // clear background
    background(255, 60, 80);
    // reset time for next interval
    time = millis();
    // debug
    println("=========================>  tick");
  }

}

For more info on millis() for a delay see this answer

Another option is to do the calculation frame based using frameCount. For example if the sketch's frameRate is about 60 fps and you want to clear roughly every 3 seconds you can check if the multiples of 180 (3 * 60) frames passed in tandem with the modulo(%) operator

import ddf.minim.*;
Minim minim;
AudioInput in;

void setup() {
  //fullScreen();
  size(300,300);
  background(255, 60, 80);

  minim = new Minim(this);
  //minim.debugOn ();
  in = minim.getLineIn(Minim.MONO, 100);
}

void draw() {
  float soundlevel;
  float distance_top = random(100);

  soundlevel = in.mix.get(0);

  stroke(255, random(90, 255));
  line(0, distance_top + soundlevel * 4000, width, distance_top + soundlevel * 1000);
  line(0, distance_top + soundlevel * 1000, width, distance_top + soundlevel * 4000);

  if(frameCount % (3 * 60) == 0){
    // clear background
    background(255, 60, 80);
    // debug
    println("=========================>  tick");
  }

}