amt coursera - imp - submission 2

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.


ANALOG SIGNAL

Q: What is an analog signal?

A: Is the one that varies continuously in time.


t

ANALOG SIGNAL

Q: What about sound?

A: Sound is a sequence of variations of pressure continuously in time.


t

DIGITAL SIGNAL

Q: And a digital signal?

A: is a representation of discrete values over time.


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.


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.

DIGITAL SIGNAL


Q: What? Ones and zeros? Like MATRIX???

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DIGITAL SIGNAL


A: not so fast. It is not as fancy as that. Actually it looks more like this:

1

0

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

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

DIGITAL SIGNAL


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).


SAMPLING


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Q: How many of those samples are taken?

A: It depends on the stablished frequency.

Samples

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)

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.

SAMPLING


Q: So what?

A: Well, it just would not fit in a CD or a DVD.

SAMPLING


Q: Oh...

A: You know who “Harry Nyquist” was?

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)”.

Shake it

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.

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.

QUANTIZATION


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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


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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


t

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

3

2

1

Volts

01 10 11

SAMPLING


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


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


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


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


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!


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

amt coursera - imp - submission 2

Technology