Part 6a

Recording Technology: Introduction

Brief History
1877 – Charles Cros and Thomas Edison describes a practical method of
recording sound on the surface of a cylinder or disc
1878 – Edison turns his idea into a working model and invents the phonograph
1888 – German immigrant Emile Berliner uses a disc instead of cylinder and
invents the “gramophone”
1900 – Danish inventor Valdemar Poulsen invents a magnetic wire recorder
1927 – Dr. Fritz Pfleumer uses a tape with magnetic particles
Types of Storage Media
 Mechanical
 Magnetic
 Optical Film
 Optical Disc
 Magneto-Optical Disc
Mechanical Recording
 This technology is the basis for all
phonograph records. The audio signal is
represented by an undulating groove on
the surface of a cylinder or disc. For
playback, the record spins on a
turntable while a lightweight “stylus”
traces the pattern wiggles in the groove.
Magnetic Recording
 The basis of all tape recording (both
audio and video). Magnetic techniques
are also used for sound tracks of some
70-mm motion picture films. In all
cases, a plastic tape or film carries a
thin coating of magnetic material,
usually iron oxide, on which a varying
magnetic pattern is imposed during
recording.
Optical Film
 This technology is used for the sound
tracks of all but few motion-picture
films. During recording, a magnetic
field varies the width of a narrow slit to
control the amount of light reaching
the sensitized film. The strength of the
magnetic field changes with the sound.
In playback, the developed film
transmits a varying amount of light to a
photocell, thus recreating the electrical
signal.
Optical Disc
 This is the basis of the compact
disc (CD) and the videodisc. The
signal is represented by a pattern of
microscopic pits along a reflective
spiral track on the disc surface. In
playback, the pattern is “read” by a
small laser and photocell.
Magneto-optical Disc
 This is the basis of the user-recordable version of the
Mini Disc, a type of compact disc.
 During recording, a layer of sensitive material beneath
the disc surface is exposed to a laser from one side and a
magnetic field from the
opposite side.
 As each location along a spiral track enters the
recording zone, it is momentarily heated by a laser, and
the magnetic field alters the optical polarization of the
heated area. In playback, these changes in polarization
are detected by an optical pickup.
Signal Format
 Analog
 Digital
 Frequency Modulation (FM)
Analog
 All sound is characterized by a pattern of rapidly varying air pressure.
 In analog recording, that pattern is imposed directly upon the storage
medium, as the undulating groove in a phonograph record, the varying
magnetic pattern in a recorded tape, or the varying light pattern of a film
sound track.
 Imperfections in the storage medium (for example, particles of dust in a
record groove) become part of the audio signal during playback.
Frequency Modulation (FM)
 Used for recording the sound and picture in videodiscs and "HiFi" video
cassettes, FM is also used in radio and television broadcasting
 The sound-wave pattern is represented by variations in the frequency of
a ‘carrier’ signal whose average frequency is above 1 megahertz (MHz).
 This approach requires complex circuitry, but it avoids the limitations of
direct analog recording.
Digital
 Digital encoding is the fundamental data processing method for most
present-day computers and for a range of sampling and recording techniques
in other fields.
 Sound is represented indirectly by a "binary“ (two-state) code in which the
recorded signal alternates between "on" and "off" states.
 Of several possible coding schemes, the most commonly used is "pulse
code modulation“ (PCM). Error-correction codes are included in the
recording, allowing near-perfect recreation of the original audio signal during
playback.
Part 6b
Recording Technology: The Phonograph
The Phonograph Record
 The phonograph record was the first successful medium for capturing,
preserving, and reproducing sound. It remained the most popular recording
medium for nearly half a century.
History
 1877 – Charles Cros and Thomas Edison describes a practical method of recording
sound waves on the surface of a disc or cylinder
 1878 – Edison turns his idea into a working model, thus crediting him as the real
inventor of the phonograph.
 1880 – Alexander Graham Bell improves on Edison’s design by using wax on the
cylinder
 1888 – German immigrant Emile Berliner demonstrated a working “gramophone”
in which sound waves are engraved in a spiral groove on a flat disc
 1901 – Berliner forms the Victor Talking Machine Company (now RCA).
Edison’s Phonograph
 Edison’s phonograph used a thin sheet of
tinfoil wrapped tightly around a pre-grooved
metal cylinder which was turned slowly by
hand.
 A conical horn focuses the sound into a
narrow apex causing a thin diaphragm to
vibrate, and a blunt needle (stylus) to inscribe
these vibrations onto the foil.
 The same apparatus is used to playback the
recorded sound, using a larger horn to amplify
the weak vibrations from the needle.
 Alexander Graham bell improved on Edison’s
design by replacing the foil with a thin layer of
wax. If desired, the wax could be shaved smooth
for a new recording
 Edison also added an electric motor to turn
the cylinder at a uniform speed
 Edison’s phonograph gave rise to “phonograph
parlors”. For a nickel per play, people had their
first experience of recorded sound
Berliner’s Gramophone
 Instead of using cylinders, Berliner’s
gramophone used a disc with a spiral
groove
 Discs could be easily reproduced from
“mother” molds by pressing
 Berliner added a spring-wound motor
to his gramophone
By 1901, he forms the Victor Talking
Machine Company, which later becomes
RCA
 Edison continued to produce cylinders up to the 1920s, but the disc had
become the dominant format by 1910
 The ease of reproduction of discs allowed discs to be priced lower than
cylinders
 Record manufacturing greatly declined during the 1930s due to the
proliferation of radio, providing endless entertainment at no cost
 By World War II, record manufacturers chose vinyl as the material of choice for
discs
The LP
 12” (30.5 cm) records only had a playing time of
less than 5 minutes until 1948
 By 1948, CBS engineers unveiled the
microgroove “LP” (long-play) record, extending
the playing time to 20 minutes per side
 This was achieved by slowing the turntable
speed from 78 to 33 1/3 rpm, and using closely
spaced grooves
 A groove 0.003” (0.0076 cm) wide made for
more tracks on the same disc
 33.33-rpm records wore out the grooves quickly due to heavy stylus pressures at
that time
 The development of the new LP included designs of low-mass tonearms
employing less tracking force (0.5 oz/14 g). By the 1980s, this force was reduced to
1 gram
 By 1949, RCA introduced a second microgroove format, a 7” (17.8 cm), 45-rpm
disc, which became the standard format for “singles”
LP Mechanism
Part 6c
Recording Technology: Magnetic Tape
History
 1888 – Oberlin Smith describes principles of magnetic
recording
 1898 –Danish telephone engineer Valdemar Poulsen patents
the first magnetic wire recorder, the Telegraphone
 1920s – 1930s – experimental ½-inch wide steel tape
were used
 1928 – a German patent was issued for a lightweight paper
tape coated with iron powder (Dr. Fritz Pfleumer)
 1936 – AEG Telefunken develops a tape recorder called the
Magnetophon and BASF worked on the tape
 1939 – Walter Weber introduces AC bias on tape recording
Valdemar Poulsen and the Telegraphone
 The Danish inventor Valdemar Poulsen (1869-1942)
is often called the "father" of magnetic recording.
 On the 1st of December 1898, he applied for a
patent on a "Telegraphone“ - a wire-recorder where
the wire was winded on a rotating drum. A magnetic
head moved and followed the wire when the drum
rotated.
 Poulsen also invented a steel-tape recorder and a
machine which used steeldisks to record on. The
steeldisk-recorder had a magnetic head, which moved
radiusly over the disk. The disc picked up speed when
the head moved into the center of the steeldisk
The Magnetic Tape
 The magnetic tape is a thin plastic ribbon consisting of
1) hard, needle-like magnetic particles composed of iron (ferric) oxide,
chromium dioxide, cobalt, or pure metal particles;
2) a plastic base material that supports the oxide
3) a binder of synthetic varnish that holds the magnetic particles and adheres
them to the base; and
4) A back coating to reduce slippage and buildup of magnetic charges
Magnetic Particles and Magnetism
 Tape recording is made possible by the ability of magnetic particles to store
electromagnetic impulses
 Certain metallic compounds are magnetized when exposed to a field of force
such a magnetic or electric current
 In tape recording, the electric current flows through the record head creating
a magnetic field that polarizes the magnetic particles on tape – arranging them
into patterns, as they move across the head
The Plastic Base
 The plastic material most commonly used for a tape’s backing is
polyester, also called mylar. It is strong, supple, and resistant to
temperature extremes as well as humidity. However, it stretches when
placed under too much tension
Magnetic Properties
Different applications of tapes require variations in their respective response
characteristics. Several measures are used to determine how suitable a tape is
for a particular recording. There are three ways to determine the tape’s ability to
retain magnetic information:
1) How strong a force field must be to change the magnetic
charge of a given particle
2) How well the tape retains magnetization once the force is
removed, and
3) How great an output level the tape can produce The terms used to describe
these measures are coercivity, retentivity, and sensitivity.
Coercivity
 Coercivity indicates the magnetic force (current) necessary to fully erase a
tape. It is measured in oersteds (unit of magnetic intensity). Standard analog
tapes have a measurement of 360 oersteds; metal particle analog tape is
between 1,200 – 1,500 oe. Digital audio tape is 1,500 oe.
 The higher the coercivity, the more difficult it is to erase the tape. A tape
recorder should be able to completely erase the tape being used.
 If the erasure is incomplete, some part of the previously recorded material
may still be heard.
Retentivity
 Retentivity is the measure of a tape’s magnetic field strength remaining after
an external magnetic force has been removed
 Retentivity is measured in gauss. A higher gauss rating means greater
retentivity, which, in turn, indicates that the tape has a greater potential output
level.
Sensitivity
 Sensitivity is similar to retentivity in that it indicates the highest output
level a tape can deliver
 Sensitivity is measured in decibels, measured against a reference tape
 Sensitivity gives a measure of the signal a tape can handle (deliver) before
it saturates – becomes fully magnetized.
Tape Transport Mechanism
Types of Heads
 Erase head – the erase head is activated during recording. Its function is
neutralize the polarities of the magnetic particles – to remove the sound
from the tape
 Record head – the record head transduces electric current into magnetic
force that magnetizes the tape. It carries two signals: the record bias, and the
signal current
 Playback head – the playback head transduces the magnetic field from the
tape back into electric energy
Tape Bias
 The response of magnetic particles on the tape is nonlinear – their
magnetic energy is not a perfect analog of the signal from the record head. A
method is needed to force the magnetic properties of the particles as the
audio current directs.
Tape Hysteresis
 The force is a high-frequency current (about 100 kHz) which is added
during recording
 The tape recorder should be adjusted for a specific tape because the bias
current affects the frequency response, distortion, and signal-to-noise ratio.
 Otherwise, a bias current set too high results in loss of high-frequencies,
and one set too low results in increased distortion and background noise.
Track Recording
Slant (Helical) Recording
Part 6d Recording Technology: Optical
Disc
History
 1877 – Thomas Edison invents the phonograph
 1887 – Emile Berliner replaces Edison's wax cylinder phonograph with the audio disc
 1958 – Invention of the LASER
 1969 – Klass Compaan, a Dutch physicist comes up with the idea for the Compact Disc
 1970 – At Philips, Compaan and Pete Kramer complete a glass disc prototype and
determine that a laser will be needed to read the information
 1980 – Compact Disc standard proposed by Philips & Sony
 1982 – First Audio CD released: 52nd St. by Billy Joel
Comparison of CD and Analog Records
Digital Sampling
 The audio bandwidth for Audio CDs is 20 to 20,000 Hz, which requires a 40
KHz sampling rate. The Red Book standard for compact disc audio adds about
a 10% margin to this, resulting in the 44.1 KHz
 Each sample is stored as 16 bits of data, which yields 65,536 values, or
32,768 discrete steps between the loudest and softest possible sounds in the
recording
The Compact Disc
 CDs are made from 120 mm diameter polycarbonate plastic discs.
 Audio CDs and CD-ROMs are manufactured by creating a master disc that is then
used to impress a pattern of pits onto the surface of the plastic blank.
 The top surface of the blank is then coated with a thin aluminum reflective
coating that is only a few hundred angstroms thick (Å = 0.1 nm).
 This coating is then covered with a 5 to 10 µm thick lacquer layer. The disc's label
is then printed on this top layer.
CD Data
Reading the Data
 The data is stored as a series of pits in the top surface of the disc
 The pits are arranged in one long spiral track, starting at the inside of the disc
 The read laser is focused on the data layer within the plastic disk, and the
reflected light bounces back through a prism to a photo sensor that varies its
voltage output based on the amount of light it receives.
 The light is more diffused when it hits a pit than when it strikes the smooth areas
between the pits (lands).
 The pits and lands do not directly represent data 1s and 0s, but as with magnetic
media, the transitions between pits and lands indicate the data.
The Optical Pickup
How Data is Arranged
 To avoid the use of small pits, Audio CDs and CD-ROM uses an Eight to Fourteen
Modulation (EFM) code for recording data.
 Essentially 8 raw data bits are converted to 14 encoded data bits so that the number
of transitions from 1 to 0 is minimized, which reduces error rates when reading data.
 This approach actually uses 17 channel bits, three of which are used for separation
between blocks. (A channel bit refers to the minimum spacing between a pit and a land,
which is the minimum distance for a transition that can indicate a bit of data.)
 The remaining 14 channel bits must have at least three channel bits per transition, but
no more than 11 channel bits per transition.
 Alternatively, looked at differently, each "1" bit is separated by at
least two"0" bits, but no more than ten 0 bits, and pits and lands are at
least 3 channel bits long, but no longer than 11 channel bits.
 There are 267 possible EFM encoding combinations, but only 256 are
required to represent the 256 possible 8-bit data combinations
Of Blocks and Frames…
 The data on the disc is arranged in frames of 588 channel bits each. Each frame stores 192 bits
(24 bytes) of data in 336 of the channel bits. The remainder of the frame's capacity is used for
synchronizing data, error correction, suppression of false low frequency sounds, and merging
with the next frame.
 Each group of 98 frames is a block, and an audio CD drive is designed to read 75 blocks per
second. The sound is recorded in stereo, so there are two audio channels.
 Each frame stores twelve 16-bit samples, so each block contains 1,176 samples.
 At 75 blocks per second, this yields 88,200 samples per second. Divide this by two to get the
samples per second for each of the two stereo channels, and you get the 44.1 KHz sampling rate
mentioned earlier.
 The drive thus reads 176.4 thousand bytes per second. Audio CDs are designed to hold up to
74 minutes, which means that they can contain up to 330,000 blocks.
The CD-ROM
 People realized that the CD would also be useful to store other types of digital data. The CD-ROM
specification soon was created.
 Data for computer programs have some requirements that are significantly different from audio
data. The most significant is accuracy.
 As a result, the CD-ROM format must have more accurate data storage than the Audio CD format.
 It uses the same 24 bytes per frame, and 98 frames make up a sector (instead of a block for the
Audio CD). This works out to 2,352 bytes per sector. Of this, 12 bytes are assigned to synchronization,
and another 4 bytes store sector header information. This leaves 2,336 bytes for storage.
 Of these, only 2,048 bytes are used for data. The remaining 288 bytes are used for Error Detection
& Correction
 With 330,000 sectors holding 2 KB apiece, the total capacity is 644.5 MB, though this is often
rounded off as 650 MB
 The CD-R
 CD-ROMs made a huge difference for the computer industry because they can hold about as much as 450
floppy disks.
 The main drawback, however, was the fact that it is relatively expensive to create the master disc used to
manufacture CDROMs.
 CD-R was the initial answer. It stands for "CD-Recordable," and is a write-once, read-many (WORM)
technology.
 Unlike magnetic media where you can erase the stored data and replace it with new data, writing data to
a CD-R disc permanently changes the surface.
 The top surface of the plastic disc is smooth with a spiral groove in it to guide the recording head. It is
then coated with a light-sensitive dye, which is subsequently coated with a reflective layer. Finally, a
protective coating is placed on top.
 Data is recorded by using a write laser beam that is stronger than the beam used to read a disc. The write
beam heats the dye layer in spots, which changes the reflectivity of the disc at that point.
CD-R Media Colors
 CD-R media comes in different colors, which is a result of the different reflective materials and
dye layers used in their construction.
 Gold was originally used for the reflective layer, but now there are also blanks with a silver
layer; this actually is a silver alloy.
 There are three dyes in common use: cyanine dye, pthalocyanine dye, and metalized azo.
 Cyanine has a cyan blue color. When used with a silver reflective layer, you get a disc that is
silver on one side and blue on the other. When a gold reflective layer is used, the gold and cyan
combine to make a shade of green, resulting in the "gold/green” discs.
 Phthalocyanine is nearly clear, it creates "silver/silver" and "gold/gold" blanks, depending on
the reflective layer.
 Metalized azo is dark blue, and results in a "silver/blue" disc when used with a silver reflective
layer.
 All CD-R media has a lower reflectivity than CD-ROMs and Audio CDs, and older
drives may have difficulty reading some types of CD-R media.
The CD-RW
 CD-RW discs and drives were created to address the WORM limitation.
 CD-RW discs rely on a different technology to record data, using a phase change material -
materials that change their properties based on how they are heated and cooled. If heated to
one temperature, it forms crystals as it cools. Heated to another temperature, it does not form
crystals.
 The crystalline state is more reflective than the amorphous, noncrystalline state. By using a
write laser with two power settings, the surface can be changed repeatedly.
 Write laser power: ~14 mW, creates an amorphous state
 Erase laser power: ~5 mW, melts the layer to a crystalline state

 The reflectivity differences between the pits and lands of the phase change materials is much
less than CD-ROM and Audio CDs, and lower than CD-R discs. As a result, most CD-ROM and
Audio CD drives cannot read CD-RW discs reliably.
My little black book…
 The compact disc standards is contained in a document called the Red Book
Specification:
 Offshoots of the CD standard came in similarly colored documents:
 Orange Book – Philip’s and Sony’s Recordable CD Standard
 Blue Book – Stamped Multisession or E-CD format
 Yellow Book – CD-ROM Standard
 White Book – Video CD Standard
 Beige Book – Kodak Photo-CD
 Green Book – Sony and Philip’s CD-i Standard
The DVD
 An acronym which stands for Digital Video Disc, and later changed to Digital
Versatile Disc.
 DVDs closely resemble CDs. Both use 120 mm diameter plastic discs that are
1.2 mm thick. They also use lasers to read data recorded in a series of pits and
lands along a spiral groove.
 As the original name implies, the DVD was primarily intended to hold movies
like the CD was for audio.
About movies…
 A typical film is 135 mins long, and even with MPEG-2 encoding, would
still require about 3.5 Mbits per second of movie.
 In addition to stereo sound, 5.1-channel sound adds another 384
kbits/s.
 There are also subtitles and other data that can come with the movie.
 Putting it together, you would need about 4.75 GB of space for a single
movie.
So, how do you…
 fit a movie on small disc?
 Originally, there was the LaserDisc™, which was 30 cm in diameter,
and you had to flip it over halfway through the movie.
The LaserDisc
 Laserdisc is an analogue format, unlike the modern CD or DVD which are
digital formats.
 Similar to the CD or DVD, a pattern of pits and lands are pressed onto the
surface of the disc.
 Whereas the pits and lands on a CD (DVD) represent digital data, with a
Laserdisc, the pits and lands are created using frequency modulation of an
analogue signal, with the frequency carrier encoded using pulse width
modulation.
 Additionally, laserdiscs have random access features similar to audio CDs and
DVDs
Squeezing it all in…
 4.75GB is roughly seven times the data you can fit on a CD. In order to squeeze
this much data onto the disc, the design elements had to be made much smaller.
 Instead of 1.6 µm between the tracks of the spiral on a CD, DVDs have a track
pitch of 0.74 µm.
 The size of the data pits shrink from 0.83 µm on a CD to 0.40 µm on the DVD.
These smaller pits require shorter wavelength light to be read reliably, so the
laser on a DVD uses light with a 640 nm wavelength, compared with a 780 nm
wavelength for CDs.
 The disc is only half as thick as a CD: 0.6 mm instead of 1.2 mm. In order to get
back to the same 1.2 mm thickness, a blank plastic 0.6 mm-thick disc is glued to
the top
More, more…
 If 4.75 GB is not enough, double-sided discs can be used, expanding the capacity to
9.4 GB.
 You can still get more storage on a single DVD disc by creating a middle data layer that
has a translucent layer behind it.
 The read laser focus gets adjusted so that it reads one layer or the other.
 However, you don't get twice the data per side - the second layer cannot be quite as
dense as the single layer can be, but you can still use this approach to get 8.5 GB on a
single-sided,
dual-layer disc.
 Use this approach on both sides of a double-sided disc for up to 17 GB of data on one
disc.
Writable and Rewritable DVDs
 Just as the natural step was the write once and then the rewritable
CD, the DVD soon followed suit.
 However, the introduction of a number of standards have made
the market more confusing.
DVD-R
 Created by Pioneer, it was originally intended to create DVD masters
prior to production.
 The specification has been split into two applications:
 General media use (DVD-R(G))
 Authoring (DVD-R(A))
 The DVD-R format is most like that of the DVD, with most discs usable in
most DVD players and DVD-ROM drives.
DVD+R
 Another writable format, developed by a coalition of developers, the DVD Alliance.
 The DVD+R format is divergent from the DVD-R format, and is in direct competition
with the it.
 There are a number of significant technical differences between the dash (or
"minus") format and the plus format, though most consumers would not notice the
difference.
 The DVD+R uses the ADIP system of tracking and speed control which is less
susceptible to interference and error than the LPP system used by DVD-R.
 Also, DVD+R(W) has a more robust error management system than DVD-R(W),
allowing for more accurate burning to media independent of the quality of the
media.
DVD-RW
 Also a Pioneer design
 Uses the same specifications for track pitch and other details,
making it physically compatible with the DVD.
 Uses a similar phase-change technology to those used in CD-RW
media.
DVD-RAM
 The DVD-RAM is considered to be a highly reliable rewritable format.
 It also uses the same phase-change technology with CD-RW.
 The discs have built-in error control and a defect management system, making it better for
general data storage, backup and archival.
 The on-disc structure of a DVD-RAM disc is closely related to hard disk and floppy disk
technology, as it stores data in concentric tracks (whereas other optical media use one long
spiral track).
 DVD-RAM discs have a pre-grooved surface. This groove is interrupted by a series of embossed
pits that contain the sector address information.
 The groove "wobbles"; it wiggles from side to side. These small changes in direction are used
to provide timing information to the drive.
 Data is written both in the grooves and on the lands between them.
DVD-RAM Disc Structure
DVD+RW
 Like the DVD-RAM, DVD+RW discs have a preformed groove and uses a
phase change material to record data.
 The groove also wobbles, but with more wobbles in a given distance to
produce a higher-frequency timing signal.
 There are no fixed address areas interrupting the grooves.
 Data is written only in the grooves.
 There are very few products supporting this technology to date.
Even more…
 By shrinking the dimensions on the CD, and using a shorter
wavelength to read the smaller pits and lands on the disc, the DVD
was born.
 DVDs provided more capacity than the CD. Can more be made out
of the 120-mm plastic disc?
Enter the Blu-Ray® Disc…
 The Blu-ray Disc (BD) is a high-density optical disc format for the storage of
digital media, including high-definition video.
 The term Blu-Ray is derived from the fact it uses a blue-violet laser (405 nm)
to read and write data onto a disc.
 The shorter wavelength means that even smaller dimensions can be read /
written on the disc, allowing even more data to stored on the standard 120 mm
disc.
 With Blu-Ray, discs can hold up to 25 GB on one side.
Physical differences of DVD and BD
The HD-DVD
 HD-DVD or high-density DVD, is designed to be the successor to
the DVD.
 It can carry 3-4 times the storage capacity of a standard DVD,
making it suitable for high-definition video.
 It also uses a 405 nm laser, similar to the Blu-Ray.
 However, technical differences make the two formats
incompatible.