Transformation domain	DFT	DCT	HT
Variance	$\begin{array}{c}\hspace{1em}{\mathit{\sigma }}_{MS}^2=\\ =M\frac{N-M}{N-1}{\displaystyle \sum _{i=1}^M\frac{y{(i)}^2}{M}}\end{array}$	$\begin{array}{c}\hspace{1em}{\mathit{\sigma }}_{MS}^2=\\ =M\frac{N-M}{N^2(N-1)}{\displaystyle \sum _{i=1}^K{A}_i^2},\end{array}$	$\begin{array}{c}\hspace{1em}{\mathit{\sigma }}_{MS}^2=\\ =\frac{(N-M)M-{(N-M)}^2}{M^2(M-1)}{\displaystyle \sum _{i=1}^K{A}_i^2}\end{array}$
		$\begin{array}{c}\hspace{1em}{\displaystyle \sum _{i=1}^K{A}_i^2}=\frac{N}{M}{\displaystyle \sum _{n\in M}^{}{s}^2(n),}\\ \\ \hspace{1em}s(n)-\mathrm{available} \mathrm{samples}\end{array}$