Transcript Overview of Recording

Overview of Recording
October 24, 2005
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A Very Quick Review (Survey)
of Electricity and Magnetism
Essential Information
for recording devices.
You have seen this before in HS or in a physics class.
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ELECTROSTATIC RUBBINGS
Think about this stuff
dead cat
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Forces Between Charges
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Attract Repel
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Coulomb’s Law – the math
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F k 2
d
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The Unit of Charge is the Coulomb.
The constant k=9 x 109 N-m2/C2
or k=9,000,000,000 N-m2/C2
d is measured in meters.
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Electrical Charge
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The negative charge is identified with electrons.
Electrons can be “pushed around” wired
(circuits) with the use of a battery.
“Resistors” impede this “current”
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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.
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Various Kinds of Electrical Materials
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Conductors
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Insulators
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Electrons move easily
Some are poor conductors – Resistors!
Electrons are held tightly in place by their
chemical bonds.
Semiconductors
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Intermediate properties
Basis of transistors.
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Charge stuff
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Potential Difference or Voltage
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Current
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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).
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Plus …
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Resistance
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The ratio of the potential difference across a
resistor (R=Ohms) to the current flowing
THROUGH the resistor.
This is Ohm’s Law
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A Magnet
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OP Survey
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Magnets come in all shapes and sizes. Almost every
refrigerator door has two to provide that last, snug
pull when it closes.
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A Changing Magnetic Field Induces a Current
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Magnets
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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??
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Other Observations
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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.
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What Reached the Ear?
This is an ANALOG signal. The ear doesn’t
respond to digital signals.
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The Process
Analog Source
Digital Storage
Convert to Analog
Retain Analog
Speaker
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Analog Storage
The Science of Music
Speaker
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Storage Methods
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Analog Storage
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Mechanical Electrical (Record, cylinder)
Magnetic (Tape, Wire)
Digital Storage
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Magnetic (Tape)
Optical (CD)
Electrical (MP3 file on your “Flash Memory”)
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Issues
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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.
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OLDEN DAYS – (Screech of Chalk)
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 bio-mechanical 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.
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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
cardboard-coated 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)
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Development - Platter
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“HIS MASTERS VOICE”
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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.
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The Need for the Microphone
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An Old Carbon Microphone
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The Microphone
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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.
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The Microphone Process
MECHANCAL
--->
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ELECTRICAL
Microphone
Signal on
a wire
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Consider a powder of
metal
Particles of Metal are pressed
closer together.
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Resistance is reduced
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How does it work?
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The “Crystal” Microphone
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The Record
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Dynamic Microphone
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Back to the Future
The Dynamic Microphone
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Movies??
Stretched
Horizontally
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1920 Wire Recorder
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1930s Magnetic Tape
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Playback
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Today
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CD
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CD
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CD OPERATION
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Latest and Greatest 0.5 GB FLASH
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FLASH MEMORY
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Back to your head
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Exploded View
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FULL CIRCLE!
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