Flanger

I found this well loved and well used 'Flanger' in my partner's study.

I had to 'google' to find out what it was:

 

"Flanging /ˈflændʒɪŋ/ is an audio effect produced by mixing two identical signals together, one signal delayed by a small and gradually changing period, usually smaller than 20 milliseconds. A flanger is an effects unit that creates this effect."

 

 

Done