filter using regular expression with variable in the pattern

Hello everyone,
I apologise for the burden of this question, as I understand Regular Expressions are some "Knights who say Ni!" serving you at the local tax office (or asking for a beer at the bar, I guess) .

I'm looking for a match from an array

var a = aafList.split("/").slice(-1).join("/").split(".").shift()

a = BBC HD audio sync test - this is what I'm looking for

if I do this:
var getVideoFile = videoFilePath.filter(x => x.match(/(BBC HD audio sync test)\.(mov|mp4|mxf)$/i))

I get my path.

How do I replace the "BBC HD audio sync test" in the regular expression with variable a ?
or aafList.split("/").slice(-1).join("/").split(".").shift(), will be as good.

Thank you so much!