With makehex.

But you need to know which Kaseikyo. The standard clearly leaves some of the details up to the manufacturer and it appears some manufacturers even do their own thing for some details the standard seems to specify.

If you tell me the form in which you have the Kaseikyo data and which manufacturer's Kaseikyo data it is, I can give you more specific instructions.

Most often when someone asks this question it is about Denon's Kaseikyo codes. In that case, just search the forum. It has already been discussed at extreme length and all the translations have already been posted.