ADC To DAC

1. The Analog to Digital Conversion Process
Joel Amulraj
Chennai, India
Week 2 Assignment

2. The Analog to Digital Conversion Process
• Sounds are analog - they are made of waves that travel through matter. People hear sounds
when these waves physically vibrate their eardrums.
• Since Computers are digital devices, they cannot understand these continuous pressure variable
analog signals, so they communicate digitally, using electrical impulses that represent 0s and 1s
( i.e., through Binary).
Binary Notations:
• One binary digit (0 or 1) is referred to as a bit, which is short for binary digit. One bit can only be
used to represent 2 different values: 0 and 1.

3. The Analog to Digital Conversion Process
• To represent more than two values, we need to use multiple bits.
• Two bits combined can be used to represent 4 different values: 0 0,
0 1, 1 0, and 1 1.
• Three bits can be used to represent 8 different values: 0 0 0, 0 0 1,
0 1 0, 1 0 0, 0 1 1, 1 0 1, 1 1 0 & 1 1 1.
• In general, 'n' bits can be used to represent 2^n different values.
20 1
21 2
22 4
23 8
24 16
25 32
26 64
27 128
28 256
29 512
210 1,024
211 2,048
212 4,096
213 8,192
214 16,384
215 32,768
216 65,536

4. Which part of the computer component converts the analog to digital information??
“The Sound Card “
The most basic sound card is a printed circuit board that translates analog and digital information:

5. The Analog to Digital Conversion Process
An analog-to-digital converter (ADC)
The ADC translates the analog waves of your voice into digital data that the computer can understand.
To do this, it samples, or digitizes, the sound by taking precise measurements of the wave at frequent
intervals.
A digital-to-analog converter (DAC)
If you were to play your recording back through the speakers, the DAC would perform the same basic
steps in reverse. With accurate measurements and a fast sampling rate, the restored analog signal can
be nearly identical to the original sound wave.

6. Capture and playback of digital audio
Air pressure
variations
Captured via
microphone
Air pressure
variations
ADC
Signal is
converted into
binary
(discrete form)
0101001101
0110101111
Analogue to Digital
Converter
DAC
Converts
back into
voltage
Digital to Analogue
Converter

7. The Analog to Digital Conversion Process
 Audio analogue to digital converters work by repeatedly
measuring the amplitude(volume) of an incoming electrical
pressure soundwave (an electrical voltage), and outputting
these measurements as a long list of binary bytes. In this way,
a mathematical "picture" of the shape of the wave is created.

8. The Analog to Digital Conversion Process
The 2 essential parameters
There are 2 important parameters which control the quality of the audio conversion process. These
are ...
Sample
rate
& Word
length
Number of
samples taken
per second.
Known as Bit
depth.
It is the number of
bits used to carry
the data in each
sample of audio.

9. Sample Rate ( in detail )
• Sample rate is the number of samples of audio carried per second, measured in Hz or kHz.
• Sampling rate defines the number of samples per second taken from a continuous signal to make a
discrete or digital signal.
• Sampling involves taking snapshots of an audio signal at very fast intervals usually tens of thousands of
times per second.
• For audio production, the least samples rate that is required is 44.1 Khz. The other sample rates are
48Khz, 88.2 Khz, 96 Khz, 192 Khz.

10. The Analog to Digital Conversion Process
 Why a minimum of 44,100 hz sample rate is required ? Nyquist theorem
It states that :
"The sample rate should be a little over twice the amount of the highest audio frequency (harmonic) to be
recorded if poor sound quality is to be avoided".
• Because humans can hear audio frequencies as high as 20KHz (20,000cps/Hz), a minimum sample rate of 44.1KHz
(or 44,100 sample measurements a second) was decided upon.,
Human audio spectrum = 20Hz to 20,000Hz (20KHz)
Highest audio frequency = 20,000Hz ... therefore ...
20,000 x 2 = 40,000 + "a little bit more" = 44,100 samples per second

11. Sampling frequency - Lowersamplerates producepoorerquality
Because of less samples,
The resulting waveform
is not a smooth
waveform like the
original waveform.

12. Sampling frequency - Higher sample rates produce better quality recordings
Because of more
samples, The
resulting waveform
is a smooth
waveform like the
original waveform.

13. The Bit Depth ( Word length )
 Bit depth is the number of bits of information in
each sample, and it directly corresponds to
the resolution of each sample.
For example in digital world, information are
represented in binary ( 0 & 1) – base 2.
For 2 bit system – 2^2 ( 4 possibilities ) are there to
represent the information.
For 8 bits it is 256 possibilities.
Such like that a 16 bit system uses 65,536
possibilities to represent the sampled frequency.

14. The Analog to Digital Conversion Process
So how many possibilities for 24 bit system?? Yes, it’s 16,777,216 possibilities
 Examples of bit depth - Compact Disc Digital Audio, which uses 16 bits per sample,
and DVD-Audio and Blu-ray Disc which can support up to 24 bits per sample.
• The longer the word length the larger the file size, the less the distortion, the better quality
the sound
• The shorter the word length, the smaller the file size, the more the distortion, the poorer
quality the sound

15. The Analog to Digital Conversion Process
Bit depth is not only used to represent the sampled frequency, but also decides the maximum amount of
amplitude ( loudness dB) that can be sampled. i.e the Dynamic Range of the signal.
 Formula for calculating the loudness = 20 log 2^n ; ( where n is the no. of bits )
 Example 1 : Calculate the loudness present in the sample rate of 44.1 khz which uses a 16 bit depth ??
20 log 2^ 16 = 96 dB
 Example 2 : Calculate the loudness present in the sample rate of 48 khz which uses a 24 bit depth ??
“ Each bit contributes to 6 dB “

16. The Analog to Digital Conversion Process
• Playing back the recorded audio in a different sample rate, changes it pitch and speed.
• Such like, if the recorded audio is played from a lower sample to a higher sample rate,
then the pitch will be sound low and the speed the song ( tempo) will also be high
• If the recorded audio is played from a higher sample to a lower sample rate, then the
pitch will sound low and the speed the song ( tempo) will also be high.

17. The Analog to Digital Conversion Process
To conclude ,
Analog to Digital conversion happens by sampling the analogue signal using binary bits ( 0 & 1)
For the conversion to happen 2 parameters are important
The Sampling Rate & The Bit Depth ( word length )
• The Sampling Rate corresponds to the frequency of the signal
• The Bit depth corresponds to the Amplitude ( DR ) of the signal

18. Conclusion
That’s it Folks, It was really interesting in doing this assignment and collecting all these details.
Learnt a lot about these conversion process and even about sampling quantization too.
Hope I have done good on this assignment. Look forward to get a good review from you. If there is
any mistake kindly correct me. Thanks for your valuable time and going through this assignment.
Joel Amulraj