\begin{equation} 
\label{eq:c2f}
\hat{f}= 
\begin{cases}
    f_{\textit{ref}}\times 2^{\hat{c}/1200}& {\textit{confi} \geq \textit{th}}\\
    0&{\textit{confi} < \textit{th}}
\end{cases}
\quad \textit{confi}=\mathop{\max}\limits_{i} \hat{y_{i}}
\end{equation}
