To do a Stitch voice impression you’ll have to constrict your larynx, use a higher-pitched voice, speak more from the throat, raise the tongue, add some Hawaiian accent and watch lots of clips where Stitch is speaking. If you can record yourself while doing the impression it’ll make it even easier to spot where you need to improve and track your progression.
First of all, try to constrict your larynx, it should feel as if your throat is compressed in a tighter, smaller area. Stitch is speaking in a consistent voice, the amplitude of his pitch doesn’t change that much unless he’s exhibiting strong emotions, in that case, it becomes significantly higher in pitch, especially when laughing. Overall, try to maintain this constriction in your throat throughout the whole impression.
Stitch’s voice is slightly higher than average, although it has some warmth to it. So, try to raise the pitch a bit when doing his voice impression but keep it minimal, you don’t need to go very high, just a tad bit.
When he’s speaking it seems like there’s this sheen added to his voice using an equalizer in post processing. If you’re recording the voice impression, you can boost 8kHz and above frequencies by a couple of dB to simulate the same effect.
Raise to the tongue
Stitch’s voice has a lot to do with the tongue placement. Try to rest the tongue against the roof of your mouth. It’ll give that warmth of his voice and help with constricting the resonance in the throat area. You should achieve a quite consistent voice.
You can place the tongue against the inside of the upper molars in your mouth and the root of your tongue should be raised a bit towards the roof of the mouth.
Listen to him speaking
As with any impression, listen to Stitch speaking a lot. This clip has plenty of those moments. Constantly listening to Stitch’s voice and manner of speech will help to learn the impression faster and more accurately.
Repeat the same phrases
Find some phrases that Stich is saying and try to repeat them in his voice, it’ll be easier than instantly speaking in random sentences. Once you master it then you can try to speak in Stich’s voice using any random sentence of yours.
Add some Hawaiian accent
Stitch is speaking in a Hawaiian accent. You can search for some Hawaiian people speaking in the accent on Youtube to help yourself get familiar with it and it’ll help to do Stitch’s voice impression.
As I listen to the Hawaiian accent they seem to overextend ‘O’ letter a lot and make their voices somewhat rounded up and softer compared to American English.
Manner of speech
Stitch speaks in abrupt, pointy sentences. He likes to have quick gaps between each word as if he’s struggling with human language and thinks about every word he’s saying in his head before articulating it. He’s not a fast talker and often speaks at a calm slow tempo.
When listening to Stitch try to catch the tempo and pauses in his sentences to figure out the manner in which he speaks, it’ll help to do a good voice impression.
Finally, record yourself to help spot flaws in your Stitch voice impression. Also, it’ll help to hear the improvement of your voice over time which could give more motivation and will be something funny to listen to later on.