Overview of Recording Fall 2007 11/12/2018 The Science of Music

ELECTROSTATIC RUBBINGS Think about this stuff dead cat - - - + - + - - 11/12/2018 The Science of Music

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. 11/12/2018 The Science of Music

Various Kinds of Electrical Materials Conductors Electrons move easily Some are poor conductors – Resistors! Insulators Electrons are held tightly in place by their chemical bonds. 11/12/2018 The Science of Music

Charge stuff Potential Difference or Voltage Current The work per unit charge required to move a charge from one point to the other Current The amount of charge that passes a single point in a circuit per unit time (1 sec). 11/12/2018 The Science of Music

Plus … Resistance The ratio of the potential difference across a resistor (R=Ohms) to the current flowing THROUGH the resistor. This is Ohm’s Law 11/12/2018 The Science of Music

A Magnet +Q S N 11/12/2018 The Science of Music OP Survey

Magnets come in all shapes and sizes Magnets come in all shapes and sizes. Almost every refrigerator door has two to provide that last, snug pull when it closes. 11/12/2018 The Science of Music

Like poles repel and unlike poles attract Like poles repel and unlike poles attract. The magnetic field lines point away from the north pole and point toward the south pole. But they don’t start or stop on those poles, they form continuous loops (inside the magnets). 11/12/2018 The Science of Music

In 1820 Hans Christian Oersted was showing his students in a lecture that the electric current in the wire did not deflect the compass needle (Figure a). When he held the compass above the wire as in Figure (b) he saw to his amazement that the compass needle deflected. Figure (c) shows the magnetic field created by the current. It is vertically downward where the compass in figure (a) was located and so couldn’t rotate the compass needle. 11/12/2018 The Science of Music

Magnet Induces a Current in a Closed Circuit A Changing Magnetic Field Induces a Current Exercise 35 Chapter 20. Electrical energy has to come from somewhere! Here the falling magnet generates current in the coil. The current has a magnetic field that interacts with the magnetic field of the falling magnet and resists its downward motion. It is conservation of energy again, the energy generating the electric current comes from the gravitational potential energy being lost by the falling magnet. 11/12/2018 The Science of Music

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?? 11/12/2018 The Science of Music

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. 11/12/2018 The Science of Music

electricity and magnetism! Now you know everything there is to know about electricity and magnetism! 11/12/2018 The Science of Music

What Reached the Ear? This is an ANALOG signal. The ear doesn’t respond to digital signals. 11/12/2018 The Science of Music

The Process 11/12/2018 The Science of Music

Storage Methods Analog Storage Digital Storage Mechanical Electrical (Record, cylinder) Magnetic (Tape, Wire) Digital Storage Magnetic (Tape) Optical (CD) Electrical (MP3 file on your “Flash Memory”) 11/12/2018 The Science of Music

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. 11/12/2018 The Science of Music

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. Sound Human Ear 11/12/2018 The Science of Music

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) 11/12/2018 The Science of Music

Development - Platter 11/12/2018 The Science of Music

“HIS MASTERS VOICE” 11/12/2018 The Science of Music

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. 11/12/2018 The Science of Music

The Need for the Microphone 11/12/2018 The Science of Music

An Old Carbon Microphone 11/12/2018 The Science of Music

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. 11/12/2018 The Science of Music

The Microphone Process MECHANCAL ---> --------------- ELECTRICAL Microphone Signal on a wire 11/12/2018 The Science of Music

Consider a powder of metal Particles of Metal are pressed closer together. Resistance is reduced 11/12/2018 The Science of Music

How does it work? 11/12/2018 The Science of Music

The “Crystal” Microphone 11/12/2018 The Science of Music

The Record 11/12/2018 The Science of Music

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Dynamic Microphone 11/12/2018 The Science of Music

Movies?? Stretched Horizontally 11/12/2018 The Science of Music

1920 Wire Recorder 11/12/2018 The Science of Music

1930s Magnetic Tape 11/12/2018 The Science of Music

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Playback 11/12/2018 The Science of Music

Today 11/12/2018 The Science of Music

CD 11/12/2018 The Science of Music

CD 11/12/2018 The Science of Music

CD OPERATION 11/12/2018 The Science of Music

Latest and Greatest Many GB FLASH MP3 ! 11/12/2018 The Science of Music

How do you squeeze all of that stuff on one iPOD? Compression! Standard CD records about 74 minutes of music. This fills 780 MB … almost a GIG! Compression makes use of what we know about our heads. 11/12/2018 The Science of Music

What do we know? If there are two tones sounding at the same time and one is much louder than the other, we would only hear the louder one. So omit the data for the softer sound. Omit other sounds that we probably won’t hear. Give up a little in fidelity. This will allow a 5 fold reduction in storage space. 11/12/2018 The Science of Music

Back to your head 11/12/2018 The Science of Music

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Exploded View 11/12/2018 The Science of Music

FULL CIRCLE! 11/12/2018 The Science of Music