Be wary of websites that ask you to download "players" or "executables" just to get an audio file. Stick to standard .mp3 , .wav , or .m4a formats.
A web-based tool that allows you to add inflections and breathing sounds to make the voice note sound more human.
If you have a microphone (or even a smartphone), recording your own version is often the best way to get the exact emotion you want. Use a free app like on a computer or the Voice Memos app on your phone. To get a professional sound, record in a small room with lots of soft surfaces (like a closet) to eliminate echo.
If you need a pre-recorded "hello," several reputable platforms offer royalty-free or Creative Commons audio:
