This document discusses digital technology and how analog signals are converted to digital format for use in computers and storage. It explains that: 1. Computers use binary digits (bits) represented as 0s and 1s rather than decimal digits. Bits are grouped into bytes of 8 bits each to represent numbers. 2. Analog signals like sound are converted to digital format by sampling the amplitude of the signal at regular intervals and assigning it a numeric value. 3. Increasing the sampling rate and precision of this process reduces sampling errors when converting back to an analog signal, improving fidelity of the reproduced sound.

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. 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. 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. Bits and bytes continued
1. 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. Analogue at a glance
1. 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. 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. 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 won't get the same rich sound
quality as you do with analogue.

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. 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. Recording the analogue way
1. In the Beginning: Etching Tin
2. 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 Edison's 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. An analogue wave
Image from
www.howstuffworks.com
Analogue Wave
The needle in Edison's phonograph is scratching onto the tin
cylinder an analog wave representing the vibrations created
by your voice. For example, here is a graph showing the
analog wave created by saying the word "hello":

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 microphone's 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
Edison's device. Notice that the waveform for the
word "hello" is fairly complex.

13. Getting in to the digital world
1. 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. 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. ……………..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. Convert the curve to numbers
• In the following figure, let's 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. 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 on
Binary form: 111 1000 1001

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. In these diagrams the
rate and the precision
have been improved