Questions for Review
1. Digital Compact Cassette (DCC) information is compressed using the Precision Adaptive Sub-band Conding system (PASC) in order to recreate decent audio files by storing a minimum amount of information. Digital Audio Tape (DAT) is similar to a CD in that all the audio content is maintained on the recorded medium.

2. Erasing on a DAT simply involves overwriting the previous signal, with either a "1" or a "0." An analog tape must be scrambled by a high frequency bias signal, before recording can begin.

3. Crosstalk is reduced on a DAT by using "azimuthal recording," in which the tape is run over a rotating head such that the tape crosses the recording head at an angle. The head for the other signal channel is oriented at a different angle, close to perpendicular with the first signal. In this way the signals don't interfere with each other.

4. DAT recordings are digital, so the tape is saturated with either a "one" or "zero," corresponding to different directions of the saturated magnetization on the tape.

5. A bias signal is not needed in digital magnetic tape recording because the tape magnetization is not in the linear regime, it is completely saturated. Only two states of magnetization are needed, to represent the two digital states "one" and "zero."

6. See numbers 4. and 5. above.

7. The dynamic range of a signal on a tape depends upon the vertical resolution of the digitization, i.e. how many bits of resolution are used to encode the amplitude of the analog audio signal. There are typically options for using 16 bits or 12 bits.

8. Two tracks are recorded for each rotation of the drum head on a DAT, labeled tracks A and B. This allows greater storage of information on the tape.

9. High densities of magnetic information are stored in the media of digital compact cassette and digital audio tape. In the former, the magnetic record is vertical and a laser is used to activate a small area of the tape for recording. In the latter, the record is vertical and a rotating drum containing two record/play heads is used to create two closely spaced tracks with compressed signals. The CD utilizes the short wavelength of infrared light to enable small pits to be discerned and read as a digital signal.

10. Vertical and horizontal magnetic recording refers to the magnetization direction on the recorded medium, in particular to its orientation with respect to the surface of the medium. Recordable mini-disc uses a terbium-iron-cobalt substrate and a recording head orientation such the that substrate is magnetized perpendicular to the surface of the disc. In this way, the information can be packed more tightly onto the disc, and the magneto-optical effect of polarization rotation (Kerr Effect) can be employed to read the information. Pre-recorded mini-disc, compact disk, digital compact cassette and digital audio tape techniques all utilize longitudinal recording, in which the magnetization on the medium is parallel to its surface.

Exercises
1. B recordable mini-disc: vertical, digital compact cassette: longitudinal
2. A. the DAT has the highest data rate...48 kHz and 16 bits
3. A. the DCC has a fixed 16 bit accuracy
4. D. when heated above the Curie temperature, a magnetic material becomes easy to magnetize
5. D. recordable mini-disc read-out is due to polarization differences between incident and reflected laser light, while the pre-recorded disc is like a CD and read-out depends on differences in the intensity of the reflected light
6. A. mini-disc playback utilize the magneto-optical (Kerr) effect
7. A. the magnetic field through the loop will point towards the top of the page, so X will be a north magnetic pole and Y will be a south pole
8. A. a laser beam on a recordable mini-disc heats a small region above the Curie temperature so that it is easily magnetized
9. B. at the normal rate of recording and playback, 48 kHz sampling rate x 16 bits resolution gives a data rate of 48,000 samples/sec x 16 bits/sample x 2 channels = 1.536 million bits/sec
10. D. two heads on a DAT are used to provide two adjacent tracks, canted to each other, providing a high density of data storage on the tape
11. B. 24 kHz is one-half the basic sampling rate on a DAT
12. E. tape hiss averages out to zero over gap of playback head
13. A. 180
14. A. standard magnetic heads orient domains at room temperature while in the magneto-optical case they are oriented at high temperatures
15. D. the DAT
16. C. an infrared laser, similar to the CD laser, is used, 3.8 x 10¹⁴ Hz
17. A. clockwise, counterclockwise, i.e. the magnetization is in opposite directions for a one and zero, so the directions of rotation are opposite
18. B. largest at the inner edge, like a CD
19. A. the pre-grooves on the mini-disc
20. D. a DCC eliminates 4/3 of the audio data and still produces excellent sound quality