Why does Ash's pikachu have a different voice

[xPikachu]

It has a slightly higher pitch than all the other pikachus'?

 

[Ryu Taylor]

It has a slightly higher pitch than all the other pikachus'?

I think they wanted to give Ash's Pikachu a distinctive identity.

 

[jnsharley13]

1. That's not always the case. See the baby/kid Pikachu in episode 25.
2. His voice actor has a high-pitched voice.
3. Too give him a separate identity from the other Pikachus.

 

[Idon'tcare]

For the record, unlike the dub (with the exceptions of Pokémon with stuff like different genders) in Japan the same species has a different VA, they do this in order to help us distinguish them easily. It's a shame that neither 4kids or TPCI have realized this, they only give the same Pokémon a different voice actor/tress when there's differences.

Speaking of which, I have added the above into my post on what I do not like about the dub version of the anime.