Edit in JSFiddle

<div ng-app="myApp" ng-controller="Playlist">
    Now playing: <input type="text" ng-model="playlist.nowPlaying"/>
    <ol>
        <li ng-repeat="sound in playlist.sounds" ng-controller="Sound">
            <b>{{sound.title}}</b>
            <button ng-click="play()">▶</button>            
            <audio
               src="http://api.soundcloud.com/tracks/{{sound.id}}/stream?client_id=YOUR_CLIENT_ID"
               playing="$index + 1 == playlist.nowPlaying">
            </audio>
        </li>
    </ol>
</div>

angular.module('myApp', []).

controller('Playlist', function($scope) {
    $scope.playlist = {
        sounds: [
            { id: 19822913, title: 'Sad Trombone' },
            { id: 19358868, title: 'Reckoning Song' },
            { id: 82841736, title: 'Every James Hetfield "Yea"... ever.' }
        ]
    }
}).

controller('Sound', function($scope) {
    $scope.play = function() {
        $scope.playlist.nowPlaying = $scope.$index + 1
    }
}).

directive('playing', function() {
    return function(scope, element, attr) {
        scope.$watch(attr.playing, function(value) {   
            if (value) {
                element[0].play()
            } else {
                element[0].pause()
            }
        })
    }
})