From man page: "If below_periods is negative, it is
treated as a positive value and is also used to indicate
the effect should restart processing as specified by
the above_periods, making it suitable for removing
periods of silence in the middle of a sound file."
However in version 12.17.7-2 (ubuntu)
sox in.wav out.wav silence 1 1 1% 1 1 1%
sox in.wav out.wav silence 1 1 1% -1 1 1%
gives the error
"sox: Periods must not be greater then zero"
a) from the man page this syntax is legal
b) Why does it warn the "Periods must not be greater
then zero" only when the period is less than zero?
c) "then" should be "than"?