question: Backmasking is a sound recording effect, that deliberately reverses which media?
answer: magnetic tape
context: Title: Jack Mullin
  Passage: John Thomas "Jack" Mullin (October 5, 1913 – June 24, 1999) was an American pioneer in the field of magnetic tape sound recording and made significant contributions to many other related fields.  From his days at Santa Clara University to his death, he displayed a deep appreciation for classical music and an aptitude for electronics and engineering.  When he died in 1999, he was buried with a rosary and a reel of magnetic tape.  A 2006 documentary movie, "Sound Man: WWII to MP3", was made about his life and contributions to sound recording.
  Title: The Midnite Sound of the Milky Way
  Passage: The Midnite Sound of the Milky Way is a garage rock compilation available on compact disc put out by Big Beat Records (UK) that consists of songs recorded at the Midnite Sound recording studio in Danville, Illinois during the 1960s.  The Midnite Sound studio one of many such venues pushing out obscure garage rock in the mid-1960s.  The set was compiled by Alec Palao, who also wrote the liner notes.  The compilation features twenty four tracks by different various artists who recorded there, and all except four have not been previously compiled.  The Midnite Sound recording were often typified by an echo-laden sound, giving them a characteristically "outer space" vibe.  The performers tended to be, even by 1960s garage rock norms, untutored and naively strange and noncommercial racket.  The groups and artists who recorded at Midnite Sound tended to be less British Invasion-influenced than most, sometimes displaying rockabilly and pre-Beatles stylistics.  The best-known act to record for the label was rockabilly/garage rocker Dean Carter, who is known for the song "Rebel Woman", which has appeared on several other compilations such as his "Call of the Wild" anthology on Big Beat Records.  He does not appear on this set, but two performers here, George Jacks and The 12th Knight, do renditions of the song.
  Title: Sound recording and reproduction
  Passage: Sound recording and reproduction is an electrical, mechanical, electronic, or digital inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects.  The two main classes of sound recording technology are analog recording and digital recording.  Prior to the development of sound recording, there were mechanical systems for encoding and reproducing instrumental music, such as wind-up music boxes and, later, player pianos.
  Title: Arista Records, LLC v. Launch Media, Inc
  Passage: Arista Records, LLC v. LAUNCH Media, Inc., 578 F.3d 148 (2d Cir.  N.Y. 2009), is a legal case brought by Arista Records, LLC, Bad Boy Records, BMG Music, and Zomba Recording LLC (collectively, "BMG") alleging that the webcasting service provided by LAUNCH Media, Inc. ("Launch") willfully infringed BMG’s sound recording copyrights.  The lawsuit concerns the scope of the statutory term “interactive service” codified in 17 U.S.C. § 114, as amended by the Digital Millennium Copyright Act of 1998 ("DMCA").  If the webcasting service is an interactive service, Launch would be required to pay individual licensing fees to BMG’s sound recording copyright holders; otherwise, Launch only need to pay “a statutory licensing fee set by the Copyright Royalty Board.”
  Title: Production sound mixer
  Passage: A production sound mixer, location sound recordist, location sound engineer or simply sound mixer is the member of a film crew or television crew responsible for recording all sound recording on set during the filmmaking or television production using professional audio equipment, for later inclusion in the finished product, or for reference to be used by the sound designer, sound effects editors, or foley artists.  This requires choice and deployment of microphones, choice of recording media, and mixing of audio signals in real time.
  Title: Backmasking
  Passage: Backmasking is a recording technique in which a sound or message is recorded backward onto a track that is meant to be played forward.  Backmasking is a deliberate process, whereas a message found through phonetic reversal may be unintentional.
  Title: Sound design
  Passage: Sound design is the process of specifying, acquiring, manipulating or generating audio elements.  It is employed in a variety of disciplines including filmmaking, television production, theatre, sound recording and reproduction, live performance, sound art, post-production, radio and video game development.  Sound design most commonly involves the manipulation of previously composed or recorded audio, such as sound effects and dialogue.  In some instances it may also involve the composition or manipulation of audio to create a desired effect or mood.  A sound designer is one who practices the art of sound design.
  Title: Low fidelity
  Passage: Low fidelity or lo fi (adjectival form "low-fidelity" or "lo-fi") is a type of sound recording which contains technical flaws that make the recording sound different compared with the live sound being recorded, such as distortion, hum, background noise, or limited frequency response.  The term "low-fidelity" is used in contrast to the audiophile term high fidelity or "hi-fi", which refers to equipment that very accurately reproduces music without harmonic distortion or unwanted frequency emphasis or resonance.  The ideas of lo-fi are taken to extremes by the genre or "scene" of no fidelity, or "no-fi".  Some lower-budget recordings from the 1970s and 1980s have an "unintended" "lo-fi" sound because of the limitations of the analog recording and processing techniques of the time, which introduced unwanted artifacts such as distortion, hum and phase problems.  In some recordings, however, high fidelity recording is "purposely" avoided, or the artifacts such as simulated vinyl record crackles are deliberately retained or added in for aesthetic or historical reasons.
  Title: Audio mixing (recorded music)
  Passage: In sound recording and reproduction, audio mixing is the process of combining multitrack recordings into a single track.  These tracks that are blended together are done so by using various processes such as EQ, Compression and Reverb.  The track may be mixed in mono, stereo, or surround sound.  There are numerous approaches, methods and techniques involved in Audio mixing; some of these practices include levels setting, equalization, stereo panning, and effects.  Audio mixing techniques and approaches can vary widely, and these can greatly affect the qualities of the sound recording.
  Title: Reverse tape effects
  Passage: Reverse tape effects are special effects created by recording sound onto magnetic tape and then physically reversing the tape so that when the tape is played back, the sounds recorded on it are heard in reverse.  Backmasking is a type of reverse tape effect.
citations: Reverse tape effects Backmasking