System identification by matlab

I am trying to determine an unknown block wherein output signal's amplitude of this block equals to a half of input signal's amplitude but remains signal feature (both input and output signal are same as can be seen in the attached figure). So what kind of unknown blocks (filters or something like that) can execute these functions? Many thank for helps.

[Star Strider]

‘... as can be seen in the attached figure ...’

Want to give that another go?