html audio muted on click play and again on click mute

I want html audio code which will fit functions: on click audio on and on click audio again off. I searched whole day and found only this code:

html

<a href="#noscroll" id="mute">toggle sound</a>

javascript

var audio = document.getElementById('background_audio');

document.getElementById('mute').addEventListener('click', function (e)
{
    e = e || window.event;
    audio.muted = !audio.muted;
    e.preventDefault();
}, false);

but this starts automaticly, I want audio start muted, then same function as it has.