Further innovations followed and continue to the present. Various buttonboard and keyboard systems have been developed, as well as voicings (the combination of multiple tones at different octaves), with mechanisms to switch between different voices during performance, and different methods of internal construction to improve tone, stability and durability. Modern accordions may incorporate electronics such as condenser microphones and tone and volume controls, so that the accordion can be plugged into a PA system or keyboard amplifier for live shows. Some 2010s-era accordions may incorporate MIDI sensors and circuitry, enabling the accordion to be plugged into a synth module and produce accordion sounds or other synthesized instrument sounds, such as piano or organ.