<?php
$size = $_FILES['audio_data']['size']; //the size in bytes
$input = $_FILES['audio_data']['tmp_name']; //temporary name that PHP gave to the uploaded file
$output = $_FILES['audio_data']['name'].".wav"; //letting the client control the filename is a rather bad idea

//move the file from temp name to local folder using $output name
move_uploaded_file($input, 'upload/'.$output);
echo 'upload/'.$output;
?>