Siegfried Loch (born 9 August 1940) is a German record producer, a record industry executive, and the founder of the ACT Music record label. As both a producer and record label pioneer, Loch is considered to have had a significant impact on the exposure, development, and success of modern jazz music, particularly European jazz.

During his career Loch has produced recordings for some of the most recognisable names in jazz, including Yusef Lateef, Eddie Harris, Joe Pass, Tim Hagans, Terri Lyne Carrington, Dave Brubeck, Vijay Iyer, Vince Mendoza, George Gruntz, Esbjörn Svensson Trio and Manu Katché; many more released albums on his ACT Music label.

Loch was born in the German town of Stolp, now Słupsk in present-day Poland. His family fled East Germany in 1951 to Hanover and initially endured financial hardship. Loch's interest in jazz developed after gatecrashing a Sidney Bechet concert in May 1956. Loch described this event as "life changing", stating in a 2020 interview:

I got into a concert by Sidney Bechet. It was the first time that I was aware of listening to jazz. This music radiated the pure joy of life and a feeling of freedom with no limitations. For me this was a moment of complete enlightenment.

He developed as a jazz drummer in the years thereafter but considered his talents insufficient to become a professional musician. He therefore resolved to remain creatively connected to jazz music by engaging in alternative job roles within the music recording industry.

In 1960, Loch joined Electrola, a German subsidiary of EMI, as a foreign sale representative, introducing him to the operations of the recording industry. By 1963, Loch had moved to Hamburg to assume label management responsibility for the jazz section of Philips. Soon afterwards he was persuaded label bosses that he should also assume production responsibilities.

Loch's first production credit was Jazz Made In Germany by the Klaus Doldinger Quartet, the first German jazz album to enjoy a global release. Other early production work was undertaken for George Gruntz, Ingfried Hoffmann, and Don Paulin. Tapping into the growing public interest in blues and rock 'n' roll emerging from outside established jazz clubs, Loch briefly diversified the label by recording and producing a number of acts tangential to German jazz, including Spencer Davis, The Searchers, and Jerry Lee Lewis. Loch's "uncomplicated" production on Jerry Lee Lewis's Live at the Star Club, Hamburg was key to capturing the band's raw and raucous performance, raising Loch's international reputation as a producer. Live at the Star Club, Hamburg has since become widely regarded as one of the greatest live rock 'n' roll albums ever recorded.

By the late 1960s, Loch had become the managing director of the German arm of the newly formed Liberty Records/United Artists label in Munich, with special responsibility for the Blue Note Records catalogue. In 1971 he became founding managing director of WEA Music Hamburg (later to become Warner Music Germany). During this time Loch continued his production activities, including a touchstone recording of Gerry Mulligan, Paul Desmond and the Dave Brubeck Trio. Loch's time at WEA enabled him to work alongside seminal Atlantic Records jazz producer, Nesuhi Ertegun, who later appointed him president of WEA-Europe in London. His ascendancy within the recording industry was reflected in his commercial successes, which some attribute to his zeal for valuing the priorities of artists and listeners, described as a "balancing act between ethics and profitability".