<audio class="wp-audio-shortcode" id="audio-140-1" preload="none" style="width: 100%;" controls="controls"><source type="audio/mpeg" src="https://www.handball-steisslingen.de/wp-content/uploads/2015/05/sound1.mp3?_=1" />https://www.handball-steisslingen.de/wp-content/uploads/2015/05/sound1.mp3</audio>

If your post contains audio, then you should use this post format. Select Audio in the appeared metabox and add link to your mp3 file.