Acid techno is a genre of techno that developed out of late 1980s Chicago acid house. Acid house was essentially house music made with a specific sound, obtained by using very distinctive instruments created mainly by Roland, such as the SH-101 and TB-303 for bass and lead sounds, and the TR-707, TR-808, and TR-909 for percussion. Acid specifically refers to the use of the Roland TB-303, or any other synthesizer designed to emulate its unique sound. While modern electronic instruments have memory banks of different sounds or patches, these machines had to be manually set by adjusting control knobs. The acid sound was obtained by either setting these controls to extreme parameters, or manipulating these controls in real-time as the track was being recorded, something record producers would call tweaking.