After doing some voice donation I got the idea that it might be a good idea to use some standard tts motor to read out the sentence and then maybe marked with a beep start the recording and let the contributor repeat the sentence.
This way I the contributor could do this while also doing something else which could gain the time that a contributor can spend on donating the voice, and maybe even allow more people to contribute which might not have the time to spend focusing on a screen.
Not sure if this would be possible from a plain webapp thoughā¦