Wake up from a pin, Sleep when work is done

Question

I have a project which needs to sleep most of the time, and when a button gets pressed, it does its thing which is producing a fading sound wave (using interrupts) until it's time to sleep again.

The goal is to reduce work load on the battery so the item can last as long as possible.

#include <avr/sleep.h>
void setup(){
  /*givePin! This is the pin that will spark the waking up!*/
  pinMode(givePin,INPUT);
  noInterrupts();
  set_sleep_mode(SLEEP_MODE_IDLE);
  /*changes to timers registers*/
  interrupts();
}
void loop(){
  ampCurrentlyOn = digitalRead(givePin);
  ampPulse =  (ampCurrentlyOn && !ampPreviouslyOn) * 255     //Reset 
           + !(ampCurrentlyOn && !ampPreviouslyOn) * ampPulse//Same
           -   bool(ampPulse);  //Decay
  ampPreviouslyOn = ampCurrentlyOn;
  
  if(!ampPulse){//Once that value reaches 0 time to GOTO bed;
    /*This! Is this what I need to do?*/
    cli();
    sleep_mode();
    sei();
  }
}

Am I doing in the right direction? Could any pin work? How do I get the chip to understand a pin set to digital HIGH to wake up from nap time?

Thank you!