MAKING WAVES

• Information travels as a series of waves
• Cycles and wavelength
• Frequency and Amplitude
• Resonance and Reflection
• Eletromagnetic waves
• Artifical Waves
• Transducers
• Analog and Digital
• Conversion between Analog and Digital
• Electromagnetic Transducers and Magnetic Media
• Common Media Terms

"Art is born of the observation and investigation of nature."
— Cicero (106 BC - 43 BC)

Information travels as a series of waves.

• Examples include light and sound waves. Electricity travels as a series of waves. Radio and television transmissions are waves.
• Waves are comprised of a state of fluctuation between potential energy and dynamic energy. A pendulum is a good example.
• A medium is an entity through which these waves pass. A medium is said to propagate waves. A medium can be anything: air, water, metal, that is stimulated.
  

The ebb and flow of wave mechanics is described as analog. Electricity is analog, and so is electronic media. But digital media is an abstraction of these waveforms; a map or grid of discrete numeric values.

Cycles and Wavelength

• Each complete change of a wave's state, from potential to dynamic energy and back, is called a cycle.
• A cycle can be measured by the distance between analogous points- a wavelength.
• A wave can be measured by the time it takes to complete a cycle, called a period.
• Waves that have similar periods from cycle to cycle are called periodic waves.
• Waves whose cycles are eratic are called aperiodic.

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Frequency and Amplitude

• Frequency is the measure of the number of waves that pass through a fixed point in a specified period of time - often measured as cycles per second. One cycle per second is called a Hertz (Hz), one thousand is Kilohertz (KHz), one million is Megahertz (MHz).
• The smaller the wavelength, the greater the frequency.
• Frequency determines pitch we hear, color we see.
• Amplitude is the measure of a wave's intensity, related to the height and depth of the wave's peaks and valleys. The amplitude relates to the loudness of sound, the brilliance of light, the strength of a signal.
• Waveform refers to the shape of a wave. The simplest of these is the sine wave. More complex waveforms arise from the vibration of more than one body. Waveforms are additive. In periodic waves, the component sine waves are multiples or harmonics of the fundamental frequency.
• Phase is the portion of a periodic wave's cycle that has elapsed from a predetermined point. Phase relationships are described in degrees, with a full cycle being 360. The zero crossing point of the wave has a value of zero degrees. The phase relationship of two waves is the degrees difference between the zero crossing points of the two waves.

LOWER FREQUENCY	HIGHER FREQUENCY

Resonance and Reflection

• An object's resonant frequency is the point at which it naturally vibrates when energy is applied.
• The angle of wave reflection is the same as the angle of incidence, except on the opposite side of normal, a line perpendicular to the reflective surface.
• Refraction is the partial reflection of a wave. A wave will be refracted if the object in its path offers absorption. Refraction is the alteration of wave velocity as the wave passes from one medium to another.
• Diffraction is the warping of a wave. A wave will be diffracted if the wavelength is equal to or greater than the size of the object in its path.

Electromagnetic waves

• Light, radio, X-ray, ultraviolet, and gamma rays require no physical media to propagate since they consist of moving fields as opposed to particles, unlike sound waves. Their wavelengths comprise the electromagnetic spectrum.
• Atoms seek to balance positive and negative forces to maintain neutral charge resulting in an electrostatic field, and positive or negative charges emitted.
• Magnetic fields emanate from the pattern of the orbit of electrons about the nucleus, resulting in North and South polarity .
• Electrostatic fields and magnetic fields can be inducted in neighboring objects.
• Follow the law of inverse squares- fields lose strength over distance from the source. (Twice the distance from the source yields one quarter the field strength).

The electromagnetic spectrum encompasses a vast range of frequencies from gamma and x-rays on one end, to a narrow band of visible frequencies sort of near the middle, to microwave and radio frequencies on the longer-wavelength end.

Electromagnetic Spectrum

Although the forms are given different names, such as X-Rays, radio waves, these are really all part of a single, continuous range, or spectrum, of electromagnetic radiation. At one end of the spectrum are the very-short-wave radiation which have the power to penetrate matter. Examples of this type are X-rays and gamma rays. Ultraviolet radiation is also penetrating but to a lesser extent. Light itself is another form of penetrating radiation, as is infrared. Somewhat longer than infrared waves are microwaves. They still have some penetrating power but the longer the wavelength the greater the absorption and deflection by materials.

Artificial Waves

Electronic waves are generally produced by a component called an oscillator.

Sawtooth wave. Used to control the color guns of a CRT.	Pulse wave. Used for timing purposes.

A triangle wave is like a sine wave except that its action is linear. It gradually builds to its maximum voltage and gradually falls to its minimum amplitude. They are used primarily in sound synthesis.

A sawtooth wave, also called a ramp wave, gradually builds to its maximum voltage/amplitude, then abruptly drops to its minimum value. It is used in the control of electronic guns for CRT displays.

A rectangular wave jumps abruptly from its minimum voltage to its maximum. This yields a series of pulses used for timing and synchronization. For this reason they are also called pulse waves. The duration of the on state is called the pulse width or duty cycle. The square wave has a 50% duty cycle yielding equal on and off times.

More complex waves can be created using a technique called modulation. This is used in radio and television transmission.

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Transducers

Conversion from one medium to another requires a transducer. An example is a microphone (to convert sound into electrical waves) and conversely, speakers that convert electrical waves into audible sound.

Conversion allows for processing of the wave.

The amplitude of the wave can increased to higher levels or reduced (attenuated) to lower levels. This is volume in audio, and brightness in video. Amplifiers are employed to boost signal strength when the signal must travel long distances or is split among many paths. Amplifiers are most often used to boost the low level electrical signal of a transducer to final program levels. Your stereo amplifier is an example.

Filtering is another way to process the wave. Cut-off filters set a level at which attenuation occurs. Low pass filters attenuate frequencies above the cut off point. High pass filters attenuate frequencies below the cut off point. A band pass filter rejects all frequencies outside a certain frequency band. A notch filter excludes only those within a certain frequency band.

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Analog and Digital

Waves and electromagnetic fields are analog, meaning thay are continuous signals capable of smooth fluctuation. Electric current is also analog. Analog is characterized by flowing current (water, air, electricity). Electricity is a current of electrons. Direct current (DC) is indicative of a one-way flow, while alternating current (AC) indicates an oscillating flow.

Analog media (videotape, audiotape) are linear media. Digital media (floppy disk, CDs) allow for random access of information. One main reason to convert analog information to digital is to facilitate access to information.

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Conversion between Analog and Digital

Analog to digital converters (ADCs) accept an analog voltage and convert it to a series of discrete numbers, called digitizing, or sampling. Digital to analog converters (DACs) transform a series of discrete numbers to a continuous analog voltage.

The sampling rate determines how often the signal is digitized. Sampling rate must be twice as high as the highest frequency to be represented. The resolution refers to how many bits are reserved to measure the amplitude of the analog wave. The greater the bit resolution, the more faithful the interpretation of the source.

Quantization occurs when a source value falls between the values at a given resolution. Aliasing occurs when the sampling rate interferes with the frequency of the program material. In general, oversampling mitigates this problem. Interpolation can be used by DACs to reconstruct missing samples.

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Electromagnetic Transducers and Magnetic Media

• Broadcasts (radio, television, cellular phones) employ artificially generated electromagnetic waves for communication.
• Audio tape, video tape, floppy and hard disks are all examples of magnetic media.
• Passing a current through a coil produces a magnetic field. Direction of the current flow dictates the polarity of the magnetic field. Moving a magnet along a wire produces a current in that direction.
• AC current flowing through a coiled wire will produce corresponding fluctuations in the magnetic field. Moving a magnet back and forth along a coiled wire will create fluctuations in the current. This principle is called electromagnetic induction.

Common Media Terms

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