Mike Beigel, an engineer whose invention helped define the sound of 1970s music, died on September 15 at his home in Mukilteo, Washington. He was 79 years old. His daughter, Romy Beigel, confirmed his passing but did not disclose a cause of death.

Beigel was best known for developing the Mu-tron III, an effects pedal widely credited with shaping the era's distinctive musical tones. The compact device, created in the early 1970s and produced by Musitronics—a New Jersey-based company he co-founded in 1972—offered guitarists a new way to manipulate sound. Known also as the "Auto Wah," it was the first commercial envelope filter pedal, producing a unique quack or bark-like sound with an underwater quality, as well as smoother swells. This technology allowed musicians to emulate synthesizer-like effects on guitars and other instruments.

The Mu-tron III found adoption among a broad array of influential artists such as Stevie Wonder, who used it on his 1973 hit “Higher Ground,” played through his Hohner Clavinet keyboard. The pedal was also favored by Frank Zappa, Chick Corea, George Benson, and Larry Coryell. Later musicians such as Flea of the Red Hot Chili Peppers and Steve Vai also adopted the effects. Jerry Garcia of the Grateful Dead used the pedal to create his signature “Jerry quack” guitar sound on songs like “Shakedown Street” and in live performances during the late 1970s. Funk bassist Bootsy Collins famously employed the Mu-tron pedals to generate his distinctive “gooey” bass tones in the mid-1970s.

Michael Lee Beigel was born on January 29, 1947, in Manhattan. After moving to Miami as a child, he displayed an early interest in electronics and music, taking apart television sets and learning guitar and saxophone. He graduated from Miami Beach Senior High School in 1964 and later earned two bachelor’s degrees from the Massachusetts Institute of Technology—one in electrical engineering and another in humanities engineering with a focus on electronic music.

Before founding Musitronics, Beigel had designed an innovative synthesizer with trumpet-like keys for the Guild guitar company. However, that project stalled after the death of Guild’s president. He then teamed up with Aaron Newman, a Guild engineer, to launch Musitronics. Under their leadership, the company developed additional pedals such as the Mu-tron Octave Divider, Phasor, Flanger, and Bi-Phase, all influential in their time and employed by artists including Neil Young, Billy Corgan, and John Frusciante.

Later in the 1970s, Musitronics’ attempt to commercialize the Gizmotron—a mechanical effects device invented by Kevin Godley and Lol Creme from the band 10cc—led to challenges. The product, aimed at making guitars sound like bowed string instruments, faced significant development hurdles and contributed to financial difficulties within the company. Notably, the Gizmotron was used by musicians like Todd Rundgren and Jimmy Page, including on Led Zeppelin’s 1979 track “In the Evening.”

After leaving Musitronics, Beigel explored new technologies, developing radio frequency identification (RFID) devices and contributing to wildlife conservation projects, including systems to monitor penguins in Antarctica and endangered tortoises in the Mojave Desert. In 2012, he founded Mu-FX and reissued updated versions of his classic pedals.

Beigel held over 40 patents throughout his career. He was survived by a sister, Nancy Schleicher, and his daughter Romy. Reflecting on his work, Beigel once said that financial gain was never his primary motivation; rather, he sought to create pioneering and excellent technologies in the field of music.