Week 7 Physics of CD Flashcards
what must be done for a CD
convert a digital signal to an analogue one
define high fidelity for a CD
high similarity between original signal and reproduced signal
define perfect reproduction for a CD
signal emitted sounds the same every time you play it
what is ADC
convert analogue wave into a stream of numbers and record these numbers to produce a digital wave
what is DAC
convert the stream of numbers from a digital wave to an analogue wave
what is sampling rate
controls how many samples are taken per second
what is sampling precision
controls how many different graduations are possible when taking a sample
how does DAC work
it takes the sampling rate and precision from the digital wave and uses them to create a new analogue wave
what is the common problem with DAC
the reproduced wave has lost some of the detail of the original wave this problem is called sampling error
how can the sampling error be reduced
increasing sampling rate and precision
describe the physical structure of a CD
1.2mm thick consisting of an injection moulded piece of clear polycarbonate plastic that covered by a series of layers of microscopic bumps made from acrylic and aluminium
how does the data of CD present
single spiral track that spirals outwards
what is used to interpret the data on a CD
optical reading system
describe what happens when a laser is absorbed, spontaneously emitted and stimulated emitted by an electron
Absorption - photon is absorbed by the electron increasing in energy level
Spontaneous emission - Electron decreasing in energy level spontaneously emits a photon
Stimulated emission - One photon is absorbed by an electron when decreasing in energy level in order to emit 2 others
what are the 3 properties of laser light that make it different to normal light and define each
1 Monochromatic - light is all of specific wavelength
2 Coherent - each photon moves in step with the others
3 Directional - beam is very tight and strong and concentrated
