SCRIPTS: Fix annoyingly bad parameters for signal view

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
FILTERS: Fix random input to the Chamberlin filter

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
FILTERS: Better mean test

The filter should not introduce any DC component, which means the mean
output may be lowered (it may even be null).

Signed-off-by: Gama <misept.dieseneuf@gmail.com>
FILTERS: Add an all-pole lowpass filter, compare it with pole-zero

Signed-off-by: Gama <misept.dieseneuf@gmail.com>