"There are two possible explanations why dogs find it hard to hear or recognise your voice over Skype. Firstly, Skype (and voice telephone systems in general) are optimised to transmit frequencies between 500Hz and 4kHz.

This provides an acceptable approximation of the frequency range of speech for human ears, but dogs have a much wider hearing range and so clipping the higher frequencies might be more significant to them than it is to us, to the point where Fido no longer recognises your voice."