gmgauthier.com/layouts/shortcodes/audio.html

<div style="text-align: center">
    <audio id="audio_player" style="width:80%" onloadeddata="set_volume()" controls>
        <source src="{{ index .Params 0 }}" type="audio/mpeg">
    </audio>
    <script>
        let audio = document.getElementById("audio_player");
        function set_volume(){
            audio.volume = 0.4;
        }
    </script>
</div>