Compress base64 encoded binary data

Question

I'm making an api request for audio files for a language learning app. The request seems to take 2-3 seconds to return, which is far too long for my needs.

I need to pass them back from my php script in the smallest way possible.

How can I send binary data, such as the requested audio file, in the fastest way possible?

Code if needed:

js request:

$.get('testPHP.php/translate_tts?ie=utf-8&tl=zh-CN&q=你好',
    function (returned_data) {
        document.getElementById("audio").innerHTML=
            '<embed src="data:audio/mpeg;base64,'+returned_data+'" hidden="true" autostart="true" loop="false"/>';

php:

$params = http_build_query(array("ie" => $_GET['ie'],"tl" => $_GET["tl"], "q" => $_GET["q"]));
$ctx = stream_context_create(array("http"=>array("method"=>"GET","header"=>"Referer: \r\n"))); 
$soundfile = file_get_contents("https://translate.google.com/translate_tts?".$params, false, $ctx); 

header("Content-type: text/plain; charset=utf-8");
header("Content-Transfer-Encoding: binary");
header('Pragma: no-cache');
header('Expires: 0');

echo base64_encode($soundfile);