Tape Distortion / Saturation

What Is Tape Saturation?

Saturation, or in this case, tape saturation, is a phenomenon that stands for analog tape recording. It describes a state where the voltage level exceeds the tape's ability to record. When the signal is sent to a tape-recorded, the voltage is sent to an electromagnet in the recording head. The plastic film (or tape) has a surface made of oxide iron powder. To record the signal on the tape, the recording head of the recorder magnetizes each iron oxide particle on the tape by varying amounts over time. This becomes a linear representation of the original alternating current, where the saturation occurs.  

Inside a Tape Recorder

In the tape recorder, for example, when the input voltage exceeds the system limit or the saturation threshold of the tape, the iron oxide molecules of the tape reach their maximum magnetic potential. In other words, they can not be polarized any further, and neither hold any more amplitude. As a result, the signal gets compressed and distorted nonlinearly. This means that when the part of the signal passes the saturation point, that part of the signal does not represent the frequencies or the amplitude of the original signal. This is the actual signal sent to the recorder; instead, it is its distorted and compressed version.  

Famous Tape Recorders

One of the famous tape recorders from the previous century that marked the sound of some of the legendary recordings is Studer J37. Swiss recording pioneer Will Studer designed this "4- 4-track machine. Released in the 1960s, the J37 was presented as Studer's first multitrack machine. It was a  true technological breakthrough, embodying versatility, functionality, and simplicity in what was then a state-of-the-art machine. In 1965, Abbey Road Studios purchased four new J37s. They used it on almost every recording until 8-track machines appeared in 1969. Following the rigorous testing process required by EMI of all equipment used at Abbey Road, they made four to the J37s. Firstly, they added wheels to make the units easily transportable. Secondly, they installed a Bulgin 3-prong socket to enable the connection of an oscillator. This was handy when using the machine at non-standard speeds. Finally, they introduced the EQ preset switch.  

Amazing Frequency Response

  The frequency response of the machine was outstanding. It was reaching 18 kHz at the high-end EQ. Along with its 52 vacuum tubes, it produced a rich spectrum of tonal colors. Part of the distinctive sound of recordings made at Abbey Road Studios during the 60s and 70s was the use of special tape formulas. EMI developed them for exclusive use in its studios. These were EMI TAPE 888 (the early '60s), EMI TAPE 811 (mid'60s), and EMI TAPE 815 (early '70s). Each possessed its unique frequency response and harmonic distortion behavior. This lent a distinctive timbre to recordings. While the J37 was used on many famous recordings, it is perhaps best known for its innovative use on The Beatles' Sgt—Pepper's Lonely Hearts Club Band. Producer George Martin utilized the machine for recording and as a creative production tool. He bounced tracks between two J37s and created layer upon layer of sound to achieve groundbreaking sonic textures.  

Additional Resources & Source Texts

• Reel-to-reel audio tape recording
• Behind the J37 Tape