Is there a way to strip the high bit of each byte in a file?

I've been trying to figure out if this can be done in sed or tr, but I can't find it. I have a bunch of files from an old Apple II which have the high bit set on each byte. On a Mac, this results in a bunch of gibberish. Of course, I could write a program to xor $80 each byte, but I'm thinking that there MUST be a way in UNIX to do this! Any ideas?