Already in the 1870s some people had started to experiment with electronically produced music. But it was not until the 1950s it began more seriously. For example there was a studio built in Köln, Germany, only for this purpose. The first synthesizer was built at RCA, USA in 1955. The synthesizers made in this early time were however very expensive and also very hard to handle. In the 1960s the first really useful synthesizers were made, for example by Don Buchla and Bob Moog. Bob Moog is the most legendary of the synthesizer producers with synthesizers like the MiniMoog and others, which has been much used by synthpop musicians. In the 1970s the production of synthesizers started in a larger scale.The first synthesizers were analogue. On those all the sounds are created by moving controls, like buttons or bars, on the synthesizer. Then they made digital synthesizers, that can be connected to each other and also to computers. They use a interface called MIDI. MIDI sends information about pitch, timbre, velocity and so on, but it doesn't send the actual sounds, just numbers representing the sounds. MIDI is now present in most personal computers. The most common sound source for modern synthesizers are samplings, i.e. digital recordings of real sounds, most of the time it's sounds from usual music instruments or from analogue synthesizers. Sometimes the different techniques are combined.