1. The Analog to Digital Conversion Process
Álvaro Montoya Thomas
March 2013
Second Submission

2. INTRODUCTION
Hi! I am Álvaro Montoya Thomas from Madrid, Spain.
This is the lesson for the 2nd week of Introduction To
Music Production at coursera.org and I am going to teach
the analog to digital conversion process.
Álvaro Montoya Thomas
March 2013
Second Submission

3. INTRODUCTION
In this assignment I am going to try to develop the topic
using Question – Answer schema.
Let's see how it works.
Álvaro Montoya Thomas
March 2013
Second Submission

4. ANALOG SIGNAL
Q: What is an analog signal?
A: Is the one that varies continuously in time.
t
Álvaro Montoya Thomas
March 2013
Second Submission

5. ANALOG SIGNAL
Q: What about sound?
A: Sound is a sequence of variations of pressure
continuously in time.
t
Álvaro Montoya Thomas
March 2013
Second Submission

6. DIGITAL SIGNAL
Q: And a digital signal?
A: is a representation of discrete values over time.
Álvaro Montoya Thomas
March 2013
Second Submission

7. DIGITAL SIGNAL
Q: Wait, wait... discrete? What do you mean, discrete?
A: OK, “discrete” means that it does not vary smoothly in
time, unlike a continuous signal.
Álvaro Montoya Thomas
March 2013
Second Submission

8. DIGITAL SIGNAL
Q: All right. How is that reprensentation then?
A: It depends. But in the computer's world it is all about 1
and 0.
Álvaro Montoya Thomas
March 2013
Second Submission

9. DIGITAL SIGNAL
Q: What? Ones and zeros? Like MATRIX???
www.cultureblues.com
Álvaro Montoya Thomas
March 2013
Second Submission

10. DIGITAL SIGNAL
A: not so fast. It is not as fancy as that. Actually it looks
more like this:
1
0
Álvaro Montoya Thomas
March 2013
Second Submission

11. DIGITAL SIGNAL
Q: uh... I see. But I do not get the point in having just 1
and 0 as data for sound :-(
A: binary data is understandable by a computer. The
reason why is called “binary” is because they are just
two: 1 and 0.
1
0
Álvaro Montoya Thomas
March 2013
Second Submission

12. DIGITAL SIGNAL
Q: Ah! Then each digit is a bit!
A: precisely. A sequence of those bits is a “word”. The
longer the sequence is, the more information can be in
there. An audio CD has 16 bits.
1
0
Álvaro Montoya Thomas
March 2013
Second Submission

13. DIGITAL SIGNAL
Q: I still do not get it.
A: Patience. Later on you will.
1
0
Álvaro Montoya Thomas
March 2013
Second Submission

14. SAMPLING
Q: Cool. How we get from the sound wave to the bits?
A: the first step is “sampling”: taking pieces of the wave
variations over time. The number of samples in time
makes the sampling frequency, which is measured in
Kilohertz (kHz).
Álvaro Montoya Thomas
March 2013
Second Submission

15. SAMPLING
Q: How many of those samples are taken?
A: It depends on the stablished frequency.
Samples
t
Álvaro Montoya Thomas
March 2013
Second Submission

16. SAMPLING
Q: Is there any recommended number?
A: The most used ones go from 24 kHz to 48 kHz but the
recommended one is
44 100 samples per second (44.1 kHz)
Álvaro Montoya Thomas
March 2013
Second Submission

17. SAMPLING
Q: Why? Let's take 100000 bits and 10000000000 kHz of
frequency to achieve the best sound ever!!!!!
A: No. It does not work like that. The more samples one
takes, the bigger the bandwidth has to be.
Álvaro Montoya Thomas
March 2013
Second Submission

18. SAMPLING
Q: So what?
A: Well, it just would not fit in a CD or a DVD.
Álvaro Montoya Thomas
March 2013
Second Submission

19. SAMPLING
Q: Oh...
A: You know who “Harry Nyquist” was?
Álvaro Montoya Thomas
March 2013
Second Submission

20. Shake it
SAMPLING
Q: Harry Nyquist? A Swedish DJ?
A: He was Swedish, but not a DJ. He was important to
make electronic music happen, though. He enunciated
the following condition together with the American
Claude Shannon:
“the minimum sample rate required to achieve a quality
digital recording has to be twice the frequency of the
audio signal to be recorded (and digitalized)”.
Álvaro Montoya Thomas
March 2013
Second Submission

21. SAMPLING
Q: All right. Then why 44.1kHz?
A: Because, as we saw last week with the Master Loudon
Stearns, the frequency of the higher notes that we can
hear is 20kHz. 44.1kHz is just more than two times that
frequency in order to get higher tones over than limit.
Álvaro Montoya Thomas
March 2013
Second Submission

22. QUANTIZATION
Q: Ah. What else is missing here?
A: The next step is “quantization”. We are going to
convert those samples into discrete values: bits.
Álvaro Montoya Thomas
March 2013
Second Submission

23. QUANTIZATION
Q: Hey, what is going on with the vertical axis? And what
is this wave?
A: Volts. Differences in tension. Those electronic values
are understood by machines. And the wave is one of the
samples.
Volts
4
3
2
1
t
Álvaro Montoya Thomas
March 2013
Second Submission

24. QUANTIZATION
Q: And how are those volts translated?
A: Here come the bits. Since they are binary, position and
amount of those 0 and 1 play an important role here. The
more digits are used, the higher numbers can be
represented.
Volts
4
3
2
1
t
Álvaro Montoya Thomas
March 2013
Second Submission

25. QUANTIZATION
Q: You mean more bits?
A: Yes. With one bit we can just choose either 0 or 1. With
two bits we have more options: 00, 01, 10, 11. As you see
they are four values: zero, one, two three.
Volts
4
3
2
1
t
01 10 11
Álvaro Montoya Thomas
March 2013
Second Submission

26. SAMPLING
Q: oh... why you do not continue with the given
example?
A: Because I need more values to represent all
the signal.
Volts
4
3
2
1
01 10 11
Álvaro Montoya Thomas
March 2013
Second Submission

27. SAMPLING
Q: What can you do? I am scared...
A: Look, let's just add one more bit.
Volts 6
5
4
3
2
1
001 010 011 100 101 110 110 110 101 100 100 001
Álvaro Montoya Thomas
March 2013
Second Submission

28. SAMPLING
Q: So you added one more possibility?
A: Not really. I doubled the possibilities. By
using one more bit we can go from 0 to 7, so
eight possibilities.
Is it always this way: from 0 to 2n-1
Volts 6
5
4
3
2
1
001 010 011 100 101 110 110 110 101 100 100 001
Álvaro Montoya Thomas
March 2013
Second Submission

29. SAMPLING
Q: Wow... but those lines were really crap.
A: Sorry, is all what I can do by drawing with Open Office.
Álvaro Montoya Thomas
March 2013
Second Submission

30. CODIFICATION
Q: I guess there is nothing else to know, is it?
A: There is still one step to consider: “codification”. The
gathered binary values are translated so that they can be
represented in your DAW.
001 010 011 100 101 110 110 110 101 100 100 001
=
123456665441
Álvaro Montoya Thomas
March 2013
Second Submission

31. THANKS FOR READING!
Q: Wow, thanks a lot. Was really helpful.
A: My pleasure. I hope this helped anyone else apart from
you!
Álvaro Montoya Thomas
March 2013
Second Submission

32. The Analog to Digital Conversion Process
Álvaro Montoya Thomas
March 2013
Second Submission