Missing $ symbol.

[cebtenzzre]

Quoting man bash, under ARITHMETIC EVALUATION:

Shell variables are allowed as operands; parameter expansion is performed before
the expression is evaluated.  Within an expression, shell variables may also  be
referenced by name without using the parameter expansion syntax.

Therefore explicit parameter expansion syntax (introduced by the $ character) is not necessary to reference the shell variable within the $((...)) (arithmetic expansion) on this line.

[ryanfox1985]

It's true, the $ symbol is not needed in this line.

I created the pr because I thought when the local player starts I hear the music distorted. I will check the equaliser, thanks!