The normal-speed TTS is definitely saying gwnaeth. I get this wrong every time as a result :-(
The difference between 'gwnaeth' and 'gwnaiff' for the synthesised voice is so marginal it's very hard to distinguish between them.
However context is useful here, 'gwnaeth' is 'I did' and so will never be associated with the word 'yfory' so maybe it's helpful to listen out for the other words in the sentence.
Should gwnaiff e Gareth yfory also be acceptable? For some reason my head insists on suggesting that.
'He will make Gareth tomorrow' - rather too unlikely!
The general order if words in Welsh is VSO - verb, subject, object - and this is particularly clear when using these short-form verbs. So:
- brathiff y gath y ci - the cat will bite the dog
- brathiff y ci'r gath - the dog will bite the cat