Modern Sound On Magnetic Tape
Scotch sensing tape was a thin strip of foil type material with a sticky background.  It was used to mark spots on recordings to indicate the beginning or ending of a particular sound track.  It became obsolete with the development of sub audible tones. 

Magnetic tape was invented for recording sound by Fritz Pfleumer in 1928 in Germany, based on the invention of magnetic wire recording by Valdemar Poulsen in 1898. Pfleumer's invention used an iron oxide powder coating on a long strip of paper. This invention was further developed by the German electronics company AEG, which manufactured the recording machines and BASF, which manufactured the tape.

After World War II, commercial development of tape-recording took off following development of reel to reel tape machines by Ampex and Magnecord and other American manufacturers in 1948. Magnetic recording became the standard for mastering music phonograph recordings and in radio broadcasting. As tape recorders became more affordable, home tape-recording became popular in the early 1950s. Development of multiple channel tape-recording led to the stereo revolution in the late 1950s. Multi-track tape also revolutionized music by allowing instruments and performances to be recorded individually for later mixing into a final cut. Also, small performance flaws could be easily corrected without re-recording the entire session.

Magnetic tape revolutionized the broadcast and recording industries. In an age when all radio (and later television) was live, it allowed programming to be prerecorded. In a time when gramophone records were recorded in one take, it allowed recordings to be created in multiple stages and easily mixed and edited with a minimal loss in quality between generations. It was also one of the key enabling technologies in the development of modern computers. Magnetic tape allowed massive amounts of data to be stored in computers for long periods of time and rapidly accessed when needed.

The great advantage of tape was twofold it allowed a performance to be recorded without the 30 minute time limitation of a phonograph disc, and it permitted a recorded performance to be edited. For the first time, audio could be manipulated as a physical entity. Tape editing was performed simply by cutting the tape at the required point, and rejoining it to another section of tape using adhesive tape, or sometimes glue. This was called a splice. The splicing tape had to be very thin to avoid impeding the tape's motion, and the adhesive carefully formulated to avoid leaving a sticky residue on the tape or deck. Usually, the cut was made at an angle across the tape so that any "click" or other noise introduced by the cut is spread across a few milliseconds of the recording. . A skilled editor could make these edits very rapidly and accurately.

This innovation was a great driving force behind the explosion of popular music in the late 1950s and 1960s. The first multi-tracking recorders had four tracks, then eight, then sixteen, twenty-four, and so on. It was also discovered that new effects were possible using multi-tracking recorders, such as phasing and flanging, delays and echo, so these innovations appeared on pop recordings shortly after multi-tracking recorders were introduced.

Reel-to-reel tape was also used in early tape drives for data storage on mainframe computers, video tape machines, and later for high quality analog and digital audio recorders in the 1980s and 1990s, before hard disk recording effectively eliminated the need for reel-to-reel technology. Studer, Stellavox, Nagra, Denon and Otari are currently making analog reel to reel recorders. The format was commercially developed in the late 1940s by American audio engineer Jack Mullin with assistance from Bing Crosby. Mullin had been a member of the U.S. Army Signal Corps during World War II. His unit was assigned to investigate German radio and electronics activities and in the course of his duties he acquired two Magnetophone recorders and fifty reels of I.G. Farben recording tape from a German radio station at Bad Nauheim, near Frankfurt. He had these shipped home and over the next two years he worked to develop the machines for commercial use, hoping to interest the Hollywood film studios in using magnetic tape for movie soundtrack recording.

Mullin gave a demonstration of his recorders at MGM Studios in Hollywood in 1947, which led to a meeting with Bing Crosby. Crosby immediately saw the potential of Mullin's recorders to pre-record his radio shows; he invested $50,000 in a local electronics company, Ampex, to enable Mullin to develop a commercial production model of the tape recorder. Using Mullin's tape recorders and with Mullin as his chief engineer, Crosby became the first American performer to master commercial recordings on tape and the first to regularly pre-record his radio programs on tape.

Ampex and Mullin subsequently developed commercial stereo and multitrack audio recorders, based on the system invented by musician Les Paul, who had been given one of the first Ampex Model 200 tape decks by Crosby in 1948. Ampex went on to develop the first practical videotape recorders in the early 1950s to pre-record Crosby's TV shows.

For home use, simpler reel-to-reel recorders were available, and a number of track formats and tape speeds were standardized to permit interoperability and prerecorded music. The first prerecorded Reel To Reel Tapes were introduced by RCA Victor Record Co. in 1954. Reel to reel was still popular through to the end of the 1970s, despite the ubiquitous cassette, mostly because of the superior quality of open reel recordings. Audiophiles are willing to accept the relative awkwardness of open reel tape to gain better quality reproduction.

Reel-to-reel tape editing also gained cult-status when many used this technique on hit-singles in the 1980s. When Ampex broke apart in the 1990s, Quantegy Inc. was formed, later becoming Quantegy Recording Solutions in 2004. Quantegy (and formerly Ampex) led the field in reel-to-reel technology, and Quantegy was the only company left making reel-to-reel tape in the world for a period of two years. Over years, magnetic tape can suffer from deterioration called sticky-shed syndrome which is caused by absorption of moisture into the binder of the tape, it can render the tape unusable.

Nowadays other technologies can perform the functions of magnetic tape. In many cases these technologies are replacing tape. Despite this, innovation in the technology continues and tape is still used.