The exploration of musical synthesizers in the 1960s was a step towards the modern keyboard. As technology became more developed, huge synthesizers evolved into portable instruments that could be used in live shows. The rapid accumulation of momentum began in 1964 when Bob Moog produced his Moog synthesizer. It used a remote keyboard and was 'modular' in design. His next generation was equipped with a built-in keyboard in 1970; the Mini-Moog. These keyboards were monophonic, along with semi-modulars like the ARP2600, and were only able to respond to one note at a time.