Analogue to digital conversion

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Analogue to digital conversion

  1. 1. Digital Technology What are binary digits?1. Computers use binary numbers, and therefore use binary digits in place of decimal digits.2. The word bit is a shortening of the words "Binary digIT."3. Whereas decimal digits have 10 possible values ranging from 0 to 9, bits have only two possible values: 0 and 1.
  2. 2. Decimal and binary numbers.• You can see that in binary numbers, each bit holds the value of increasing powers of 2. That makes counting in binary pretty easy• E.g 1011 means• 1 * 23) + (0 * 22) + (1 * 21) + (1 * 20) = 8 + 0 + 2 + 1 = 11• Some more examples• 10 = 1010 11 = 1011 12 = 1100 13 = 1101 14 = 1110 15 = 1111 16 = 10000
  3. 3. Bits and bytes.1. Bits are rarely seen alone in computers.2. They are almost always bundled together into 8- bit collections, and these collections are called bytes.3. With 8 bits in a byte, you can represent 256 values ranging from 0 to 255, as shown here: 0 = 00000000 1 = 00000001 2 = 00000010 ... 254 = 11111110 255 = 11111111
  4. 4. Bits and bytes continued1. CD uses 2 bytes, or 16 bits, per sample. That gives each sample a range from 0 to 65,535, like this:2. 0 = 0000000000000000 1 = 0000000000000001 2 = 0000000000000010 ... 65534 = 1111111111111110 65535 = 1111111111111111
  5. 5. Analogue at a glance1. As a technology, analogue is the process of taking an audio or video signal (in most cases, the human voice) and translating it into electronic pulses.2. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s.
  6. 6. Analogue to Digital (A to D)1. Digital technology breaks your voice (or television) signal into binary code—a series of 1s and 0s—transfers it to the other end where another device (phone, modem or TV) takes all the numbers and reassembles them into the original signal.2. The beauty of digital is that it knows what it should be when it reaches the end of the transmission.
  7. 7. Is the duplication perfect?1. Like any technology, digital has a few shortcomings.2. Since devices are constantly translating, coding, and reassembling your voice, you wont get the same rich sound quality as you do with analogue.
  8. 8. Can we use the digital phone using an analogue line?• There are digital-to-analog adapters that not only let you use analog equipment in a digital environment, but also safeguard against frying the internal circuitry of your phone, fax, modem, or laptop.• Some adapters come designed to work with one specific piece of office equipment: phone, modem, laptop, or teleconferencer. Simply connect the adapter in between your digital line and your analog device.
  9. 9. Comparing Analogue Vs. Digital• http://telecom.hellodirect.com/docs/Tutorials /AnalogVsDigital.1.051501.asp Visit the above site for more details of Analogue Vs. Digital
  10. 10. Recording the analogue way1. In the Beginning: Etching Tin2. Thomas Edison is credited with creating the first device for recording and playing back sounds in 1877. His approach used a very simple mechanism to store an analog wave mechanically.3. In Edisons original phonograph, a diaphragm directly controlled a needle, and the needle scratched an analog signal onto a tinfoil cylinder . (see the clip in the link below)4. http://communication.howstuffworks.com/analog- digital1.htm
  11. 11. An analogue wave Image from www.howstuffworks.comAnalogue WaveThe needle in Edisons phonograph is scratching onto the tincylinder an analog wave representing the vibrations createdby your voice. For example, here is a graph showing theanalog wave created by saying the word "hello":
  12. 12. Analogue recording cont….1. The waveform was recorded electronically rather than on tinfoil, but the principle is the same.2. What the graph is showing is, essentially, the position of the microphones diaphragm (Y axis) over time (X axis).3. The vibrations are very quick -- the diaphragm is vibrating on the order of 1,000 oscillations per second.4. This is the sort of wave scratched onto the tinfoil in Edisons device. Notice that the waveform for the word "hello" is fairly complex.
  13. 13. Getting in to the digital world1. In a CD (and any other digital recording technology), the goal is to create a recording with very high fidelity (very high similarity between the original signal and the reproduced signal) and perfect reproduction (the recording sounds the same every single time you play it no matter how many times you play it).2. To accomplish these two goals, digital recording converts the analog wave into a stream of numbers and records the numbers instead of the wave.3. The conversion is done by a device called an analog-to- digital converter (ADC).4. To play back the music, the stream of numbers is converted back to an analog wave by a digital-to-analog converter (DAC).5. The analog wave produced by the DAC is amplified and fed to the speakers to produce the sound.
  14. 14. Converting an analogue wave to digital wave • http://communication.howstuffworks.com/an alog-digital3.htm Here is a typical wave (assume here that each tick on the x-axis represents 1/1000 of a second):
  15. 15. ……………..contd…• When you sample the wave with an analog-to- digital converter, you have control over two variables:• The sampling rate - Controls how many samples are taken per second• The sampling precision - Controls how many different gradations (quantization levels) are possible when taking the sample
  16. 16. Convert the curve to numbers• In the following figure, lets assume that the sampling rate is 1,000 per second and the precision is 10: 1. The green rectangles represent samples. 2. Every one-thousandth of a second, the ADC looks at the wave and picks the closest number between 0 and 9.
  17. 17. 3. The number chosen is shown along the bottom of the figure.4. These numbers are a digital representation of the original wave.Digital reading: 7 8 9 and so onBinary form: 111 1000 1001
  18. 18. 1. When the DAC recreates the wave from these numbers, you get the blue line shown in the following figure: 2. You can see that the blue line lost quite a bit of the detail originally found in the red line, and that means the fidelity of the reproduced wave is not very good.3. This is the sampling error. You reduce sampling error by increasing both the sampling rate and the precision
  19. 19. In these diagrams therate and the precisionhave been improved

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