Was the iconic ‘frog bass’ sound in Michael Jackson’s Thriller created using the “toy-like” Casiotone CT-401?

A whole lot of classic gear was used during the making of Michael Jackson’s Thriller album, but it turns out that one of the most memorable sounds from it may have come from a very unexpected, “toy-like” source: the Casiotone CT-401.

In the video above, synth programmer Anthony Marinelli, who worked as a synth programmer on Thriller, goes in search of the source of the famous ‘frog bass’ sound that pops up in the breakdown to the album’s title track (the bit with the VIncent Price voiceover in it) and went on to inspire key parts of the choreography in the song’s iconic video.

Marinelli seeks out his old friend Steven Ray, who worked as a production assistant on Thriller, who believes that the sound may well have come from the CT-401 - or another Casiotone of a similar vintage - and you don’t have to look too hard on this basic preset keyboard in order to find it. There’s literally a button marked ‘Frog’; press this, play a low-pitched note and the sound is right there.

As Ray remembers it, producer Quincy Jones and his team knew that they wanted another sound in the breakdown - “Quincy was all about adding layers and elements,” he says - and auditioned various keyboards in a bid to find it. Jones eventually brought in the CT-401 from his house, Ray believes, and the rhythmic part was played by session supremo Greg Phillinganes, who Marinelli previously enlisted to help record a recreation of the full Thriller arrangement.

Ray says that the fact that the CT-401 was rarely used in professional circles - it was “the last keyboard you would expect to be found in a major recording session,” he recalls - was one of the reasons it was chosen, with its “toy-like” sound being the perfect fit. The tone might be ‘cheap’, but it really cuts through, which helps to explain why everyone remembers it.

Case closed, then? Not quite, as Marinelli says that he’s also heard that it may have been either James Ingram or Thriller co-writer Rod Temperton who suggested the sound. Both are now deceased, sadly, but Marinelli reports that he has plans to talk to other people who were in the room during the Thriller sessions to get a definitive answer on how the frog sound was spawned…