10-24-05 the science of music 1 overview of recording october 24, 2005

10-24-0510-24-05 The Science of MusicThe Science of Music 11

Overview of RecordingOverview of Recording

October 24, 2005October 24, 2005


A Very Quick Review A Very Quick Review (Survey) of Electricity and (Survey) of Electricity and

MagnetismMagnetism

Essential InformationEssential Information

for recording devices.for recording devices.

You have seen this before in HS or in a physics class.


ELECTROSTATIC RUBBINGSELECTROSTATIC RUBBINGSThink about this stuffThink about this stuff

- - - + - + - -

dead cat


Forces Between ChargesForces Between Charges

QQ11 QQ22AttracAttractt

RepelRepel

++ ++ XX

++ -- XX

-- ++ XX

-- -- XX

Q1 Q2

F F


Coulomb’s Law – the mathCoulomb’s Law – the math

The Unit of Charge is the The Unit of Charge is the Coulomb.. The constant k=9 x 10The constant k=9 x 1099 N-m N-m22/C/C22

or k=9,000,000,000 N-mor k=9,000,000,000 N-m22/C/C22

d is measured in meters.d is measured in meters.

221

d

QQkF


Electrical ChargeElectrical Charge

The negative charge is identified with The negative charge is identified with electrons.electrons.

Electrons can be “pushed around” wired Electrons can be “pushed around” wired (circuits) with the use of a battery.(circuits) with the use of a battery.

““Resistors” impede this “current”Resistors” impede this “current” Ohm’s Law: V=iROhm’s Law: V=iR

Electrons are components of atoms. An Electrons are components of atoms. An Atom contains a nucleus of protons and Atom contains a nucleus of protons and other junk. The protons are the other junk. The protons are the fundamental positive charges.fundamental positive charges.


Various Kinds of Electrical Various Kinds of Electrical MaterialsMaterials ConductorsConductors

Electrons move easilyElectrons move easily Some are poor conductors – Resistors!Some are poor conductors – Resistors!

InsulatorsInsulators Electrons are held tightly in place by their Electrons are held tightly in place by their

chemical bonds.chemical bonds. SemiconductorsSemiconductors

Intermediate propertiesIntermediate properties Basis of transistors.Basis of transistors.


Charge stuffCharge stuff

Potential Difference or VoltagePotential Difference or Voltage The work per unit charge required to move a The work per unit charge required to move a

charge from one point to the othercharge from one point to the other CurrentCurrent

The amount of charge that passes a single The amount of charge that passes a single point in a circuit per unit time (1 sec).point in a circuit per unit time (1 sec).


Plus …Plus …

ResistanceResistance The ratio of the potential difference The ratio of the potential difference

across a resistor (R=Ohms) to the across a resistor (R=Ohms) to the current flowing THROUGH the resistor.current flowing THROUGH the resistor.

This is Ohm’s LawThis is Ohm’s Law


A MagnetA Magnet

S NS N +Q

OP Survey


Magnets come in all shapes and sizes. Almost every refrigerator door has two to provide that

last, snug pull when it closes.


A Changing Magnetic Field Induces a Current

Magnet Induces a Current in a Closed Circuit


MagnetsMagnets

Magnets Do NOT attract chages.Magnets Do NOT attract chages. Magnetism is a very different Magnetism is a very different

phenomenon. phenomenon. Magnets have N and S polesMagnets have N and S poles Like poles repelLike poles repel Unlike poles attractUnlike poles attract Where have we seem this before??Where have we seem this before??


Other ObservationsOther Observations

A magnet moving into a coil produces A magnet moving into a coil produces an electric current (and voltage!).an electric current (and voltage!).

A wire moving near a magnet will A wire moving near a magnet will have a current generated in it.have a current generated in it.

There is a “magnetic field” around a There is a “magnetic field” around a wire.wire.

A loop of wire acts like a small A loop of wire acts like a small magnet.magnet.


What Reached the Ear?What Reached the Ear?

This is an ANALOG signal. The ear doesn’t respond to digital signals.


The ProcessThe Process

Analog Source

Digital Storage Analog Storage

Convert to Analog Retain Analog

Speaker Speaker


Storage MethodsStorage Methods

Analog StorageAnalog Storage Mechanical Electrical (Record, cylinder)Mechanical Electrical (Record, cylinder) Magnetic (Tape, Wire)Magnetic (Tape, Wire)

Digital StorageDigital Storage Magnetic (Tape)Magnetic (Tape) Optical (CD)Optical (CD) Electrical (MP3 file on your “Flash Electrical (MP3 file on your “Flash

Memory”)Memory”)


IssuesIssues

We want the process to be fast.We want the process to be fast. We want to be able to widely We want to be able to widely

distribute the recorded product.distribute the recorded product. We want the product to reproduce, as We want the product to reproduce, as

well as possible, the original sound.well as possible, the original sound. We want to ENJOY the final We want to ENJOY the final

reproduction.reproduction.


OLDEN DAYS – (Screech of OLDEN DAYS – (Screech of Chalk)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.

Sound

Hum

an

Ear


GramophoneGramophoneThe 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)


Development - PlatterDevelopment - Platter


“HIS MASTERS VOICE”


Western ElectricWestern 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.


The Need for the The Need for the MicrophoneMicrophone


An Old Carbon An Old Carbon MicrophoneMicrophone


The MicrophoneThe Microphone

The microphone is a device that The microphone is a device that received the sound vibrationsreceived the sound vibrations

converts it to an electrical “signal”converts it to an electrical “signal” Which is then sent to the next stage Which is then sent to the next stage

in the process (later).in the process (later). The signal tends to be small and gets The signal tends to be small and gets

weaker as it travels down a long wire.weaker as it travels down a long wire.


The Microphone ProcessThe Microphone Process

MicrophoneMicrophone

Signal onSignal ona wirea wire

MECHANCAL ---> ---------------MECHANCAL ---> --------------- ELECTRICAL ELECTRICAL


Consider a powder ofConsider a powder ofmetalmetal

Particles of Metal are pressed closer together.

Resistance is reduced


How does it work?How does it work?


The “Crystal” The “Crystal” MicrophoneMicrophone


The RecordThe Record


Dynamic MicrophoneDynamic Microphone


Back to the FutureBack to the FutureThe Dynamic MicrophoneThe Dynamic Microphone


Movies??Movies??

StretchedStretchedHorizontallyHorizontally


1920 Wire Recorder1920 Wire Recorder


1930s Magnetic Tape1930s Magnetic Tape


Playback


TodayToday


CDCD


CD OPERATIONCD OPERATION


Latest and Greatest 0.5 GB Latest and Greatest 0.5 GB FLASHFLASH


FLASH MEMORYFLASH MEMORY


Back to your headBack to your head


http://www.electronixwarehouse.com/car/woofers/main.htm


Exploded ViewExploded View


FULL CIRCLE!FULL CIRCLE!

10-24-05 the science of music 1 overview of recording october 24, 2005

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