How to decode URL encoded audio binary in APIGEE?

[#1]

I used Javascript Policy.
I tried below.

var decodedURI = decodeURIComponent("RIFF%A4%01%00WAVE.......")

However, the following errors occur.

Execution of JavaScript-1 failed with error: Javascript runtime error: "URIError: Malformed URI sequence.

Please tell me the way that URL encoded data to binary or base64encoded data?