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The Analog to Digital Conversion Process
Álvaro Montoya ThomasMarch 2013
Second Submission
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 ThomasMarch 2013Second Submission
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 ThomasMarch 2013Second Submission
ANALOG SIGNAL
Q: What is an analog signal?
A: Is the one that varies continuously in time.
Álvaro Montoya ThomasMarch 2013Second Submission
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ANALOG SIGNAL
Q: What about sound?
A: Sound is a sequence of variations of pressure continuously in time.
Álvaro Montoya ThomasMarch 2013Second Submission
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DIGITAL SIGNAL
Q: And a digital signal?
A: is a representation of discrete values over time.
Álvaro Montoya ThomasMarch 2013Second Submission
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 ThomasMarch 2013Second Submission
DIGITAL SIGNAL
Álvaro Montoya ThomasMarch 2013Second Submission
Q: All right. How is that reprensentation then?
A: It depends. But in the computer's world it is all about 1 and 0.
DIGITAL SIGNAL
Álvaro Montoya ThomasMarch 2013Second Submission
Q: What? Ones and zeros? Like MATRIX???
www.cultureblues.com
DIGITAL SIGNAL
Álvaro Montoya ThomasMarch 2013Second Submission
A: not so fast. It is not as fancy as that. Actually it looks more like this:
1
0
DIGITAL SIGNAL
Álvaro Montoya ThomasMarch 2013Second Submission
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
DIGITAL SIGNAL
Álvaro Montoya ThomasMarch 2013Second Submission
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
DIGITAL SIGNAL
Álvaro Montoya ThomasMarch 2013Second Submission
Q: I still do not get it.
A: Patience. Later on you will.
1
0
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 ThomasMarch 2013Second Submission
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
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Q: How many of those samples are taken?
A: It depends on the stablished frequency.
Samples
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
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)
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
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.
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
Q: So what?
A: Well, it just would not fit in a CD or a DVD.
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
Q: Oh...
A: You know who “Harry Nyquist” was?
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
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)”.
Shake it
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
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.
QUANTIZATION
Álvaro Montoya ThomasMarch 2013Second Submission
Q: Ah. What else is missing here?
A: The next step is “quantization”. We are going to convert those samples into discrete values: bits.
QUANTIZATION
Álvaro Montoya ThomasMarch 2013Second Submission
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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.
4
3
2
1
Volts
QUANTIZATION
Álvaro Montoya ThomasMarch 2013Second Submission
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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.
4
3
2
1
Volts
QUANTIZATION
Álvaro Montoya ThomasMarch 2013Second Submission
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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.
4
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2
1
Volts
01 10 11
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
Q: oh... why you do not continue with the given example?
A: Because I need more values to represent all the signal.
4
3
2
1
Volts
01 10 11
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
Q: What can you do? I am scared...
A: Look, let's just add one more bit.
6
5
4
3
2
1
Volts
001 010 011 100 101 110 110 110 101 100 100 001
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
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
6
5
4
3
2
1
Volts
001 010 011 100 101 110 110 110 101 100 100 001
SAMPLING
Álvaro Montoya ThomasMarch 2013Second Submission
Q: Wow... but those lines were really crap.
A: Sorry, is all what I can do by drawing with Open Office.
Q: Wow... but those lines were really crap.
A: Sorry, is all what I can do by drawing with Open Office.
CODIFICATION
Álvaro Montoya ThomasMarch 2013Second Submission
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
=
1 2 3 4 5 6 6 6 5 4 4 1
THANKS FOR READING!
Álvaro Montoya ThomasMarch 2013Second Submission
Q: Wow, thanks a lot. Was really helpful.
A: My pleasure. I hope this helped anyone else apart from you!
The Analog to Digital Conversion Process
Álvaro Montoya ThomasMarch 2013
Second Submission