Did you know that there are 3 ways to pronounce "ed" at the end of a word?

There is a tendency for people learning English to always pronounce the “ed” at the end of a word as a separate syllable. This, of course should only be done when the letter before the “ed” is d or t.

I was curious to see what the Web had to say about this and was surprised to learn that the other words can be divided into two groups. link

If the sound before the “ed” is voiced then the “ed” is pronounced as d, otherwise as t. This is a fairly subtle distinction, and I am not quite convinced that the sound of “ed” is ever really a d. Is there such a thing as an unvoiced d sound, or is the only distinction between d and t that d is voiced and t is unvoiced.