Why doesn't playing audio stop other tasks?
Since the CPU works in fixed clock cycles, nothing is really continuous, only seems so because the discretization is sensitive enough.

Suppose your CPU clock rate is $1\text{GHz}=10^9Hz$. If the CPU only devotes one in $t$ clock cycles to processing audio (and utilizes the remaining clock cycles for unrelated tasks) then you have a delay of $\approx t\cdot 10^{-9}s$ between every "audio processing tasks" preformed by the cpu (for simplicity, we assume the cpu preforms this processing using only one clock cycle).

Lets say we allow a delay of $10^{-5}s$ (humans hear frequencies in the range of 20Hz to 20Khz, so the human hearing will not be sensitive to such delay), then we need to require $t&lt;10^4$, so the CPU can handle simultaneously $10^4$ more tasks while keeping a delay of $10^{-5}s$.