1039Chapter 28
Magnetic Recording and Playback
by Doug Jones and Dale Manquen
28.1 Introduction........................................................................... 1041
28.1.1 The Family of Magnetic Recording Devices............................................... 1042
28.1.2 Tape Recorder as a Transformer........................................................ 1042
28.1.3 Changes with Time and Space......................................................... 1042
28.2 Tape Transports....................................................................... 1043
28.2.1 Tape Metering..................................................................... 1043
28.2.1.1 Tape-to-Capstan Contact Enhancement.............................................. 1046
28.2.1.2 A Word of Caution Regarding Urethanes............................................. 1046
28.2.2 Flutter............................................................................ 1047
28.2.3 Tape Tensioning.................................................................... 1047
28.2.3.1 Capstan-Derived Tensioning...................................................... 1048
28.2.3.2 Spooling-Motor-Derived Tensioning................................................ 1049
28.2.4 Tape Guiding...................................................................... 1050
28.2.4.1 Tape Height................................................................... 1051
28.2.4.2 Head Azimuth..................................................................... 1051
28.2.4.3 Tape Guides................................................................... 1052
28.3 Magnetic Heads....................................................................... 1053
28.3.1 Geometric Characteristics............................................................. 1053
28.3.1.1 Gap Length Loss................................................................ 1053
28.3.2 Spacing Losses and Thickness......................................................... 1055
28.3.2.1 Equalization Boosts............................................................. 1056
28.3.2.2 Fringing...................................................................... 1057
28.3.2.3 Contour Effect................................................................. 1057
28.3.2.4 Crosstalk...................................................................... 1058
28.3.3 Frequency Characteristics............................................................. 1058
28.3.3.1 Inductive Rise.................................................................. 1058
28.3.3.2 Hysteresis Loss................................................................. 1058
28.3.3.3 Eddy Current Loss.............................................................. 1058
28.3.4 Combined Characteristics............................................................. 1059
28.3.5 Noise............................................................................. 1059
28.3.5.1 Track Width................................................................... 1060
28.3.5.2 Thermal Noise.................................................................. 1060
28.3.5.3 Barkhausen Noise............................................................... 1060
28.3.5.4 Magnetostrictive Noise........................................................... 1061
28.3.6 Record Heads...................................................................... 1061
28.3.6.1 Biased or Anhysteretic Recording................................................... 1062
28.3.7 Erase Heads....................................................................... 1063
28.3.8 Head Degaussing (Demagnetizing)..................................................... 1064
28.3.9 Tape Components................................................................... 1065