High quality voice
You may be confronted with this dialog on some Android devices.
This means that your phone came with a normal voice, but it is low quality to save space on your phone. You can download a better sounding voice if you like - and if you have space on your phone. You should click the 'Do not show again' check box, as it will keep asking if you hit cancel. It is not required that you download a higher quality voice. Note that you can also change voices - see here