add meta box using function.php

function add_meta_boxes() {
     add_meta_box(
          'repeatable-fields',
          'Audio Playlist',
          'repeatable_meta_box_display',
          'post',
          'normal',
          'high');

     add_meta_box(
          'wpa-45985',
          'Wordpress Answers Metabox',
          'wpa_meta_box_display',
          'post',
          'normal',
          'high');

} add_action('admin_menu', 'add_meta_boxes');

just define a 2nd metabox, then define its display function and save function. it is exactly the same. EXCEPT, that if you want to save it as a different meta entry then you will change the name attribute for all the new inputs.

for example: your first metabox has the name=”custom_audio[]”, so to save the 2nd box in a different meta entry you’d name the meta inputs differently

<input type="text" name="wpa_45985['input1']" />
<input type="text" name="wpa_45985['input2']" />

and all your meta in this box will be saved in the meta key wpa_45985

edit#1: adding display and save callbacks. you should add some data sanitation to the save function but this should be a good start

function wpa_meta_box_display() {
    global $post;
    wp_nonce_field( 'wpa_45985', 'wpa_45985_nonce' );


$meta = get_post_meta($post->ID, 'wpa_45985', true);

$foo = isset($meta[foo]) ? $meta[foo] : '';
$bar = isset($meta[bar]) ? $meta[bar] : '';
?>
<input type="text" class="widefat" name="wpa_45985[foo]" value="<?php echo $foo; ?>"/>
<input type="text" class="widefat" name="wpa_45985[bar]" value="<?php echo $bar; ?>"/>


<?php

}

add_action('save_post', 'wpa_meta_box_save');
function wpa_meta_box_save($post_id) {
    global $custom_meta_fields;
    if ( ! isset( $_POST['wpa_45985_nonce'] ) ||
        ! wp_verify_nonce( $_POST['wpa_45985_nonce'], 'wpa_45985' ) )
        return;

    if (defined('DOING_AUTOSAVE') && DOING_AUTOSAVE)
        return;

    if (!current_user_can('edit_post', $post_id))
        return;

    update_post_meta($post_id,'wpa_45985',$_POST['wpa_45985']);

} ?>