Also central to his sound was the agidigbo both plucked and struck to create a hypnotic ostinato at the center of the apala sound .
The agidigbo is a hollow lamellophone ( thumb piano ) .
Also central to his sound was the agidigbo , a hollow lamellophone ( thumb piano ) , both plucked and struck to create a hypnotic ostinato at the center of the apala sound .