With a multifaceted career as a classical and Jazz French Hornist, multi-instrumentalist and sought-after sound engineer, Heidi Trefethen shuttles back and forth across continents frequently, in roles both onstage and off. As a hornist, she has performed in numerous ensembles and venues in Italy, the UK, Bosnia, Thailand, Guatemala, Israel Turkey, and the US, including the LA Philharmonic, the JazzUp Festival in Italy, Cleveland's Rock n' Roll Hall of Fame, San Francisco's Davies Symphony Hall and SFJAZZ's Miner Hall. Heidi has repeatedly been awarded the first position for Horn with the annual Rome Festival Orchestra and Il Teatro dell'Opera di Roma, and on special invitation, played with Giasscritto and Ottomania, two jazz ensembles of Rome’s Teatro dell’Opera, under Claudio Cimpanelli’s direction. Most recently she taught a Master Class and performed for the Horn Studio Mahidol University in Bangkok, Thailand with her horn duo, MediusTerra.

A self-taught pianist at age two, Heidi took up the French horn after being inspired by The Seattle Symphony and as a middle school student, began playing with the Seattle Youth Symphony. Following a move to Southern California, she was awarded a full scholarship to the Idyllwild Arts Academy. She then continued her studies of horn performance and pedagogy at Brigham Young University, where she won principal positions in the university’s elite chamber orchestra, as well as its philharmonic orchestra and chamber groups, led by conductor and former Vienna Philharmonic principal violist Clyn Barrus.

As a live sound engineer, she has worked with the likes of Shawn Colvin, Meshell N'degeocello, Odetta, Ellis Paul, Joan Baez, Joan Armatrading, Buffy Sainte-Marie, Holly Near, John Stewart of the Kingston Trio, Dar Williams, Al Stewart, Jane Siberry and Lucy Kaplansky, often at the legendary Freight and Salvage in Berkeley, CA. Heidi can be often seen behind the sound boards at SFJAZZ where she was recently recruited as a FOH and A2 engineer. 

As a recording engineer, she studied at the California Recording Institute’s intensive sound engineering program. An internship at the historic Coast Recorders and a job at Rocket Lab mastering house had her working side-by-side with technical heavyweights John Cuniberti, Dan Alexander and Michael Romanowski. Heidi’s engineering credits include Tammy Hall’s “Blue Soul,” Jessica Jones and Mark Taylor’s “Live at the Freight” 2011, Lucy Kaplansky’s "Kaplansky Sings Kaplanksy," 2000, Michael Burles' currently "Untitled Recording" 2017, Nestler and Hawtin's "Duality" 2014, co-engineered with Bryan Bell, Herbie Hancock’s first engineer, and full production of Anne Rainwater's solo piano recording of Johann Sebastian Bach's Goldberg Variations, to be released in the Fall of 2018.​

Heidi successfully auditioned for the San Francisco Conservatory of Music and the Berklee College of Music. While in Boston preparing to begin her Film Scoring and Audio Engineering studies at Berklee, she studied with the principal hornist of the Boston Philharmonic. Fate then stepped in and Heidi’s trip to Italy to play in the Rome Festival turned into a three-year stay where she performed with Il Teatro dell'Opera di Roma. She returned Stateside fluent in Italian and connected to an international community of musical peers.

Heidi is a composer of electronic, classical, folk, and rock music and is regularly engaged to arrange horn and string parts for folk and pop music artists. Scoring for film remains her favorite mode of composition and her music can be heard in "Love Lost or Something Like It", 2013, a short film by Melanie Graysmith shown at San Francisco's legendary Castro Theater, several short animated films, and is currently scoring a short film for release in the Fall of 2018.

Heidi also led the SF-based four-piece folk-pop band, Whoa Nellie, as songwriter, guitarist and backing vocalist. They performed for several years throughout the Bay Area and released a self-titled EP. In 1999, Heidi also composed an album of contemporary folk songs, which she recorded with Amy Reber, Whoa Nellie’s lead vocalist.

Heidi began playing trombone in 2011 and plays in an 11-piece R&B/soul cover band, the Grove Valve Ensemble, winners of the 2012 FORTUNE Battle of the Corporate Bands at the Rock and Roll Hall of Fame in October 2012.

Her recent engagements include membership as the French Hornist in the SFJAZZ Center Monday Night band, recording sessions at Skywalker Sound for the Marin Youth Symphony, and freelancing in the Bay Area for the Santa Rosa Symphony, Symphony Napa Valley, Santa Cruz Symphony, Silicon Valley Symphony, among other Bay Area ensembles. She can be seen in various performances with Jazz pianist Tammy Hall and finishing their recording, Dialogue. Heidi is a revered educator and teaches Music Production, Mixing Mastering and Recording, Film Scoring, and Audio For Visual Media at SFJAZZ's Digital Lab. Very passionate about promoting women in the audio and music fields, Heidi currently mentors 4 women, including a collaboration with between SFJAZZ and a San Francisco Unified School District high school teacher creating a Digital Music Program for students to be rolled out in all SFUSD music programs.