You're free to use the generated voices for any purpose - no attribution needed. As mentioned above, the downloaded audio uses external voices which may be different to your device's local ones.

If you don't know how to install more voices, and you can't find a tutorial online, you can try downloading the audio with the download button instead. Many operating systems (including some versions of Android, for example) only come with one voice by default, and the others need to be downloaded in your device's settings. Note: If the list of available text-to-speech voices is small, or all the voices sound the same, then you may need to install text-to-speech voices on your device. You can even use it to reverse the generated audio, randomly distort the speed of the voice throughout the audio, add a scary ghost effect, or add an 'anonymous hacker' effect to it. For example, you can make the voice sound more robotic, or like a giant ogre, or an evil demon. Want more voices? You can download the generated audio and then use voicechanger.io to add effects to the voice. If you don't like the externally-downloaded voice, you can use a recording app on your device to record the 'system' or 'internal' sound while you're playing the generated voice audio. You can download the audio as a file, but note that the downloaded voices may be different to your browser's voices because they are downloaded from an external text-to-speech server. This web app allows you to generate voice audio from text - no login needed, and it's completely free! It uses your browser's built-in voice synthesis technology, and so the voices will differ depending on the browser that you're using.

Microsoft sam voice generator