I wasn't so sure. Look at the above frequency response thresholds. Dogs can hear higher frequencies than we, but miss out on the lower. When a dog hears your voice, it hears supersonic details we don't, and misses the lower register. It doesn't hear what you hear.
Below find the response curve for a "Wadia 861, Filter A, CD." The response curve is nice and flat--until it falls off. It keeps up with the low register, which the dogs don't notice anyway, but it misses out on the high end, which we don't care enough about to instrument. (Why bother? Dogs don't buy electronics.)
The bulk of the energy spectrum for human speech is below 1000Hz, but there's still about a percent or so above human hearing range. Does 1% matter? I guess that dogs wouldn't have that kind of sensitivity unless it made a difference--maybe in finding mice. I wonder if anybody has tested dog response to human voices with signal response flat out to 30-40 kHz.