I know the snr after μ-law compression is
$\text{SNR}\approx\frac{3L^2}{[\ln(1+ \mu)]^2}$ when $\mu \gg \frac{\max_t m(t)}{\text{rms}(m(t))}$,
where $m(t)$ is the message signal, and
$L$ the number of levels.
Can anyone give the idea how it came or the proof?