Types of Video Signals

Question 1

What are the four synchronization pulse regions of interest?

Answer 1

The front porch, the sync pulse, the active video region, and the back porch

Question 2

What is the front porch?

Answer 2

The front porch is the time between the end of active video information and the beginning of the sync signal.

Question 3

What is the back porch?

Answer 3

The back porch is the time between the end of a sync pulse and the beginning of active video.

Question 4

What does the video receiver or monitor look for?

Answer 4

As each sync pulse comes along, the video receiver or monitor “looks” for the leading edge of the sync pulse.

Question 5

What does the leading edge do?

Answer 5

The leading edge acts to synchronize the display with the video source.

Question 6

What are the two types of electronic video signals?

Answer 6

Electronic video signals are of two types: Analog or Digital.

Question 7

What does an analog video consist of?

Answer 7

An analog video signal consists of a low voltage signal containing the intensity information for each line, in combination with timing information that ensures the display device remains synchronized with the signal.

Question 8

How is an analog video signal often represented?

Answer 8

An analog video signal is often represented as a sine wave, where the vertical axis represents the signal amplitude, or brightness attribute of the video image, and the horizontal axis represents the changes in frequency which affects the sharpness or detail in the image. Changing the wave’s amplitude represents the different colors on the screen.

Question 9

Analog signals vary in amplitude over time and can represent an infinite number of values or levels between its highest and lowest points. A typical analog video signal has a voltage range of ___to ___ volts peak-to-peak.

Answer 9

A typical analog video signal has a voltage range of zero to 0.7 volts peak-to-peak.

Question 10

Common analog video signal information is transmitted as a series of horizontal lines separated by _____________ _______, which have the appearance of a ___ ____, or ___ ____.

Answer 10

Common analog video signal information is transmitted as a series of horizontal lines separated by synchronization pulses, which have the appearance of a digital pulse, or square waves.

Question 11

How is an image drawn on a TV or computer display?

Answer 11

An image is drawn on a TV or computer display by sweeping an electronic signal horizontally across the display one line at a time.

Question 12

What does the horizontal sync pulse at the end of each line ensure?

Answer 12

The horizontal sync pulse at the end of each line ensures synchronization of the display to the beginning of the next line of information.

Question 13

One complete set of lines forms the picture, or frame. Upon the completion of one frame, the scanning process returns vertically to the top left corner of the screen to repeat the process. The number of scanned lines determines the ____ ______of the image and the rate at which an entire picture is formed is called the_____ ____.

Answer 13

The number of scanned lines determines the vertical resolution of the image and the rate at which an entire picture is formed is called the refresh rate.

Question 14

There are two different types of scanning systems, _____and _____, which differ in their technique used to format the picture on the screen. Essentially, TV signals and compatible displays are _______while computer signals and compatible displays are _______(non-?).

Answer 14

There are two different types of scanning systems, interlaced and progressive, which differ in their technique used to format the picture on the screen. Essentially, TV signals and compatible displays are interlaced while computer signals and compatible displays are progressive (non-interlaced).

Question 15

What is interlaced scanning?

Answer 15

Interlaced scanning is where each frame is divided into two separate fields, with one field composed of odd-numbered horizontal scan lines and the other composed of even-numbered horizontal scan lines. The picture is displayed on the screen by scanning the lines on an alternating basis.

Question 16

What is progressive scanning?

Answer 16

Progressive scanning is a method by which all the video scan lines are presented on the screen in one pass instead of two. It is typically denoted by the letter “p”, as in “480p”, which indicates a signal with 480 active lines running at 60 frames per second.

Question 17

How is progress scanning typically denoted?

Answer 17

It is typically denoted by the letter “p”, as in “480p”, which indicates a signal with 480 active lines running at 60 frames per second.

Question 18

Digital video signals are considerably different in comparison to analog signals, with specific performance and timing requirements that must be maintained throughout the entire signal path. How are digital signals represented?

Answer 18

Digital video signals are represented as square waves consisting of almost instantaneous transitions between two states: ON or OFF. There are no in-between states in digital signals as there are in analog signals.

Question 19

For digital signal transmission, what does a digital receiver circuit need to determine?

Answer 19

For digital signal transmission, a digital receiver circuit needs only to determine whether each incoming bit is ON or OFF to completely reconstruct the transmitted signal.

Question 20

Some early versions used a voltage level of about 3.7 to 5.0 volts to signal an ON condition and zero volts to signal an OFF condition. What signal level do most digital formats used today operate at?

Answer 20

Most digital formats used today operate with a peak-to-peak signal level of 0.8 to 1.0 volts for signaling an ON condition.

Question 21

What is among the benefits of digital technology?

Answer 21

Among the benefits of digital technology is the ability for digital media and AV equipment to communicate bi-directionally with each other.

Question 22

Communication between content, sources, the AV system, and displays consists of the signal capabilities of devices in the system, or information related to rights and permissions associated with the transmitted content.

Three of the most important digital communication types are:

Answer 22

Three of the most important digital communication types are:

• EDID—Extended Display Identification Data
• DRM—Digital Rights Management
• HDCP—High-Bandwidth Digital Content Protection

Question 23

What does EDID mean?

Answer 23

EDID – Extended Display Identification Data

Question 24

What is EDID?

Answer 24

EDID is a data structure used to communicate video display information, including native resolution and vertical interval refresh rate requirements to a source device. The source device will then output the optimal video format for the display based on the provided EDID information, ensuring proper video image quality.

Question 25

What is DRM?

Answer 25

Digital Rights Management is a generic term for technologies, such as content scrambling in cable or satellite television transmission, that can be used to control access to, or reproduction of copyrighted, commercially-available content. DRM is used primarily to prevent the unauthorized duplication and distribution of copyrighted material.

An AV system that is intended to support playback of protected content must be compliant with the associated DRM. Failure to do so may result in an inability to display this protected material.

DRM also governs how content can be used. Commercially-available DVDs and Blu-ray Discs, for example, are typically licensed for personal use in a residential environment. Displaying this content in a public venue without express consent of licensing by the copyright holder is in violation of the media’s license.

Question 26

What is HDCP?

Answer 26

HDCP – High-Bandwidth Digital Content Protection

Question 27

What is the most common DRM scheme?

Answer 27

The most common DRM scheme is HDCP—High-Bandwidth Digital Content Protection, developed by Intel, to prevent the copying of digital video and audio content.

Question 28

What is the 3 step HDCP process HDCP enabled video sources, such as Blu-ray Disc players, PCs, and other digital media devices always undergo to protect the video from unauthorized access?

Answer 28

1.Authentication: The video source determines that all devices connected to its outputs are authorized and able to receive encrypted video. This is accomplished by means of an initial authorization handshake protocol, where cryptographic public keys and encrypted messages are exchanged between the source and the downstream devices connected to its outputs.

2. Content Encryption: After the source authenticates that all downstream devices are HDCP compliant and that no system size restrictions are violated, the source sends encrypted video downstream. The source periodically revises the encryption key for the video as an additional security measure.
3. Renewability: Since HDCP relies on digital encryption using secret keys, the system can be circumvented if the secret keys residing in HDCP-licensed products fall into the wrong hands. Therefore a means has to be established to revoke any compromised keys. This is done through a list of public keys of compromised products which are then compared to downstream devices.