Everyone may not be able to sing with the voice of their favorite or greatest singers, but everyone can hum the melodies. You know the melodies of your favorite songs, and sometimes you may not know the words, but you have the timing.
With the invention of the karaoke machines, many wannabe singers discover the real lyrics when they are displayed on a screen to view.
The invention of the karaoke machine allowing the person only to hum the melodies would be a sure hit.
Yeah, I know the words are important, but the audience would be spared the horror of listening to someone intoxicated attempting to sing the lyric to many classic standards like Aretha Franklin’s “Respect.” & the Beatles “Hey Jude.”
YouTubes has many people attempting to sing using a karaoke machine, and if you click on the links, your ears will appreciate the original song and just sing the melody.
Expedition Nomadic Adventures 
Thank you so much for your comment. :-)