The toc de castells is the tune to play during a castells performance. Its main purpose is to communicate to those in the tower (who cannot see) what stage the tower is in.
Each colla can have their own interpretation of the tune, which is why you will find different groups playing it slightly differently. However the main theme is instantly recognisable. For now, in the Edinburgh colla, we will adopt the arrangement used by the Castellers del Poble Sec.
Here's how you would play the Toc alongside a castell.
I have produced backing tracks to help you practice at home! They are made for a flaviol in G, and there are a few different versions available. I recommend using YouTube's playback speed settings to slow the video down if you are not confident with the tune yet.
Here the full track with both voices and drum. Below that you can find links to versions that have one of the parts muted, so that you can fill in the missing part, or so you can hear the existing parts clearer.