Unformatted text preview: Overview of Recording
November 2, 2007 07/24/11
07/24/11 Storage 1 A Very Quick Review (Survey) of Electricity and Magnetism
for recording devices.
You have seen this before in HS or in a physics class. 07/24/11
07/24/11 Storage 2 ELECTROSTATIC RUBBINGS
Think about this stuff dead cat - 07/24/11
07/24/11 - - + Storage - + - - 3 Forces Between Charges 07/24/11
X + X Q2 + Q1 F Q2 + F Q1
Storage Attract Repel
4 Coulomb’s Law – the math Q1Q2
F =k 2
d The Unit of Charge is the Coulomb.
The constant k=9 x 109 Nm2/C2
or k=9,000,000,000 Nm2/C2
d is measured in meters. 07/24/11
07/24/11 Storage 5 Electrical Charge The negative charge is identified with electrons.
Electrons can be “pushed around” wired (circuits) with the use of a battery.
“Resistors” impede this “current” Ohm’s Law: V=iR Electrons are components of atoms. An Atom contains a nucleus of protons and other junk. The protons are the fundamental positive charges. 07/24/11
07/24/11 Storage 6 Various Kinds of Electrical Materials Conductors Insulators Electrons move easily
Some are poor conductors – Resistors! Electrons are held tightly in place by their chemical bonds. Semiconductors 07/24/11
07/24/11 Intermediate properties
Basis of transistors.
Storage 7 Charge stuff Potential Difference or Voltage Current 07/24/11
07/24/11 The work per unit charge required to move a charge from one point to the other
The amount of charge that passes a single point in a circuit per unit time (1 sec). Storage 8 Plus … Resistance The ratio of the potential difference across a resistor (R=Ohms) to the current flowing THROUGH the resistor. 07/24/11
07/24/11 V=iR This is Ohm’s Law Storage 9 A Magnet +Q S N 07/24/11
07/24/11 Storage OP Survey
10 Magne com in all shape and size Alm e ry re rator door
ost ve frige
has two to providethat last, snug pull whe it close
07/24/11 Storage 11 07/24/11
07/24/11 Storage 12 07/24/11
07/24/11 Storage 13 A Changing Magnetic Field Induces a Current 07/24/11
07/24/11 Storage 14 Magnets Magnets Do NOT attract chages.
Magnetism is a very different phenomenon. Magnets have N and S poles
Like poles repel
Unlike poles attract
Where have we seem this before?? 07/24/11
07/24/11 Storage 15 Other Observations A magnet moving into a coil produces an electric current (and voltage!).
A wire moving near a magnet will have a current generated in it.
There is a “magnetic field” around a wire.
A loop of wire acts like a small magnet. 07/24/11
07/24/11 Storage 16 What Reached the Ear? This is an ANALOG signal. The ear doesn’t respond to digital signals. 07/24/11
07/24/11 Storage 17 The Process
Convert to Analog Processing Retain Analog Speaker 07/24/11
07/24/11 Analog Storage Storage Speaker 18 Storage Methods Analog Storage Mechanical Electrical (Record, cylinder)
Magnetic (Tape, Wire) Digital Storage 07/24/11
07/24/11 Magnetic (Tape)
Electrical (MP3 file on your “Flash Memory”)
Storage 19 Issues We want the process to be fast.
We want to be able to widely distribute the recorded product.
We want the product to reproduce, as well as possible, the original sound.
We want to ENJOY the final reproduction. 07/24/11
07/24/11 Storage 20 OLDEN DAYS – (Screech of Chalk)
07/24/11 Bell's ear Phonautograph was a very unusual variation on the basic technology. The recording mechanism was the human ear. By removing a chunk of skull including the inner ear from a human cadaver, and attaching a stylus to the moving parts of the ear, he was able to use this biomechanical device to make a recording of the sounds that entered a recording horn. It recorded on a moving glass strip, coated with a film of carbon, so there are probably no original recordings from it. Storage 21 Gramophone The graphophone in its original form was an improved form of the phonograph. One main difference, which Edison would soon adopt, was the use of a cardboardcoated wax cylinder instead of a sheet of tinfoil. The exact construction of the cylinders and the materials used changed considerably in later years, though the basic concept of recording into a soft, plastic material was retained. (image from NMAH) 07/24/11
07/24/11 Storage 22 Development Platter 07/24/11
07/24/11 Storage 23 “HIS MASTERS VOICE” 07/24/11
07/24/11 Storage 24 Western Electric
Western Electric's recorder used electronic amplifiers to drive an electromagnetic cutting head, rather than relying on the acoustic horn. The result was a louder, clearer record. 07/24/11
07/24/11 Storage 25 The Need for the Microphone 07/24/11
07/24/11 Storage 26 An Old Carbon Microphone 07/24/11
07/24/11 Storage 27 The Microphone The microphone is a device that received the sound vibrations
converts it to an electrical “signal”
Which is then sent to the next stage in the process (later).
The signal tends to be small and gets weaker as it travels down a long wire. 07/24/11
07/24/11 Storage 28 The Microphone Process
MECHANCAL > ELECTRICAL Microphone 07/24/11
07/24/11 Storage Signal on
a wire 29 Consider a powder of
metal Particles of Metal are pressed closer together. 07/24/11
07/24/11 Resistance is reduced30 Storage How does it work? 07/24/11
07/24/11 Storage 31 The “Crystal” Microphone 07/24/11
07/24/11 Storage 32 The Record 07/24/11
07/24/11 Storage 33 07/24/11
07/24/11 Storage 34 Dynamic Microphone 07/24/11
07/24/11 Storage 35 Movies?? Image is
07/24/11 Storage 36 1920 Wire Recorder 07/24/11
07/24/11 Storage 37 1930s Magnetic Tape 07/24/11
07/24/11 Storage 38 07/24/11
07/24/11 Storage 39 Playback 07/24/11
07/24/11 Storage 40 Yesterday and Today Symphony ~ 35 Disks @ 78 RPM ~50% of CD 07/24/11
07/24/11 Storage 41 CD 07/24/11
07/24/11 Storage 42 CD 07/24/11
07/24/11 Storage 43 CD OPERATION 07/24/11
07/24/11 Storage 44 Latest and Greatest 0.5 GB FLASH 07/24/11
07/24/11 Storage 45 FLASH MEMORY 07/24/11
07/24/11 Storage 46 Back to your head 07/24/11
07/24/11 Storage 47 07/24/11
07/24/11 Storage 48 07/24/11
07/24/11 Storage 49 Exploded View 07/24/11
07/24/11 Storage 50 Full Circle 07/24/11
07/24/11 Storage 51 ...
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- Fall '07