One of the cardinal rules of computer dictation is that you always must have a high quality microphone. This was drilled into me years ago. A funny thing happened though. The software and hardware got a lot better. About six months ago I started dictating frequently on my retina MacBook Pro without an external microphone. Instead, I’m just talking to my computer without anything plugged into it. This works remarkably well. I know that Apple added a noise canceling microphone with this most recent batch of computers. Your mileage may vary depending on what machine you’re driving but if you’re using a recent Mac, and you haven’t tried dictation without a microphone, you should.