Sound, Copyright

Goal

By the end of today, you should:

1. understand differences between analog and digital signals

2. understand sampling rate, bit resolution, bit rate and calculating file size

3. understand the basics of Copyright law

4. know how to apply rules of fair use

Recap of Analog and Digital

Our ears interact with an analog world of sound waves, but music and other sounds are all being done digitally now. Why? How?

• Analog signals alwasy degrade with time, distance and other factors.
• With an analog signal, you can't be entirely sure of what the original sound was supposed to be out of the literally infinite number of possibilities.
• Digital signals are only tranmitting one of two possible values (zero and one). Each is a bit.
• Therefore, when the receiver gets a degraded signal, it can make an informed guess about which of the two possibilities was actually transmitted. This allows the signal to be cleaned-up.
• Furthermore, by adding redundant information in the form of parity bits, errors can be detected.
• By using additional parity bits, the receiver can figure out which bit is erroneous and, since there are only two possible values, errors can be corrected.
• Thus, it is possible, using digital representations, to have perfect transmission.

Have I convinced you? Good. So, how do we do it? How do we represent sound digitally?

• Imagine drawing the analog signal on graph paper. Make two crucial decisions:
  • The resolution on the vertical axis, and
  • the resolution on the horizonal axis.
• The horizontal axis will be time.
• Sample the analog signal at each vertical line (each moment in time), rounding it off at the nearest horizontal line. Write this down as a number.
• The sequence of numbers is then the digitized signal.
• The resolution of the vertical axis (how close together the horizontal lines are) determines the number of bits per sample. Usually, this is some nice round number like 8, 16 or 32 bits per sample.
• The resolution of the horizontal axis (how close together the vertical lines are) determines the sampling rate.
• The product of these two gives the bit-rate.
• The greater the bit rate, the better the receiver can reconstruct the original signal.
• The Nyquist theorem tells us how high the sampling rate has to be in order to capture sounds up to a given maximum frequency (pitch).

Quiz Question Nr. 1

Sound travels faster in:

1. vacuum

2. water

3. air

4. speed doesn't depend on the medium

Quiz Question Nr. 2

A soprano's singing (with an orchestra) can be considered as sound with:

1. Low amplitude, low pitch

2. Low amplitude, high pitch

3. High amplitude, low pitch

4. High amplitude, high pitch

Quiz Question Nr. 3

Analog signals are superior to digital signals.

1. True

2. False

3. There is no difference between the two.

Quiz Question Nr. 3b

Digital signals are superior to analog because

1. Errors can be avoided

2. Errors can be detected

3. Errors can be corrected

4. Signals can be compressed

Quiz Question Nr. 4

When will the parity bit NOT be able to detect an error:

1. When there is an odd number of bits in the transmission.

2. When there is an even number of bits in the transmission.

3. When the number of changed bits is even.

4. When the number of changed bits is odd.

Quiz Question Nr. 5

Assume that the even parity bit indicates that there has been an error in transmission, what is our best option?

1. There is nothing we can do about it, noise is part of every transmission.

2. We can use the parity bit to identify the error and fix it.

3. We can use error correction algorithms to reconstruct the original signal.

4. We will have to request for the signal to be retransmitted.

Quiz Question Nr. 6

The bit resolution is:

1. The sampling rate.

2. A multiple of the fundamental frequency.

3. The number of bits to represent frequency values.

4. The number of bits to represent amplitude values.

Quiz Question Nr. 7

If the whales can produce sound in the range 10 Hz - 30 KHz, at what frequency we would have to sample to produce a digital recording?

1. 15 KHz

2. 20 KHz

3. 30 KHz

4. 45 Khz

5. 60 KHz

Task 1: File Size Calculations

Knowing that the bit rate is the number of bits to represent one second of digital sound, write jQuery/Javascript code that will perform the calculations for the form shown below.

The statements for reading the content from the fields is already given, you need to write two functions that take paremeters and return values and invoke them. Read comments in the execution box.

<form>
<p>Bit Resolution: <input name="resolution"></p>
<p>Sampling Rate: <input name="sampling"></p>
<p>Time (in seconds): <input name="seconds"></p>
<p>The Bit Rate is: <span id="bitrate"></span></p>
<p>The File Size is: <span id="filesize"></span></p>
</form>

Copyright and Fair Use

Digital information has qualitatively changed the effect of copyright protection. Now that perfect copies are instantly available, the incentive to make illegal copies is enormous.

Copyright

• is for physical expression of a work (you can't copyright ideas).
• is automatic
• is for a limited duration, after which the work goes into the public domain.
• is different from intellectual credit. That is, plagiarism is different from violating copyright.

The courts also acknowledge the importance of fair use of copyrighted works. It depends

• on the purpose and character of the use.
• on the nature of the copyrighted work
• on the amount or substantiality of the use.
• on how the use affects the potential market of the copyrighted work.

Copyright law is for the benefit of society, not solely for the benefit of the copyright holder.

Quiz Question Nr. 8

When does a written work receive protection under U.S. copyright laws?

1. when you write it down

2. when you publish your work

3. when you register your work with the U.S Copyright Office

Quiz Question Nr. 9

1. Yes

2. It depends

3. No

Quiz Question Nr. 10

1. Yes

2. It depends

3. No

Activity

With those around you, skim over these open-ended questions and choose one to discuss. We'll collect thoughts afterwards.

Summary

We hope that after these activities you can:

• understand digital signals and how they are transmitted
• sampling for conversion between analog and digital signals
• copyright law and fair use

Solutions

Will be posted later, visit again after .

function calculate_bitrate(bRes, sRate){
  return bRes * sRate;
}
$("#bitrate").text(calculate_bitrate(bitRes, sampling));

function calculate_filesize(bRes, sRate, seconds){
  var bitrate = calculate_bitrate(bRes, sRate);
  return bitrate * seconds / (8*1000); // convert in KB
}
$("#filesize").text(calculate_filesize(bitRes, sampling, seconds));