var mute = false;

function changeVolume(el) {
    if (mute == false) {
        mute = true;
        el.innerHTML = 'Ton ein';
        el.className = 'mute';
        document.getElementById('corp_sound').SetVariable('vol', 0);
    } else {
        mute = false;
        el.innerHTML = 'Ton aus';
        el.className = '';
        document.getElementById('corp_sound').SetVariable('vol', 60);
    }
}