Cassette-Tape Delay

Inoue et al. [43] has developed a derivative technique using a modified cassette recorder connected to a spectrophotometer. The same absorption spectrum was recorded on two separate parallel channels of a magnetic-tape cassette as frequency modulated (FM) analog signals with a slight shift in wavelength (--I nm). Then the difference between the output signals from these channels was recorded (Fig. 3-6). 

Theoretically, not only the first derivative but also higher-order derivatives can be generated by connecting two or more of these apparatus in series. But this has not been attempted to date, perhaps because of the difficulties arising with synchronization and interference due to signal noise. 

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