CBT - Certified Broadcast Technologist Audio and Video Signals Questions and Answers

Question 1

In an analog NTSC composite video signal, what is the primary function of the colorburst?

Accepted Answer

To provide a frequency and phase reference for the chrominance signal.

Answer

The colorburst is a short burst of the color subcarrier sine wave (approximately 3.58 MHz for NTSC) placed on the 'back porch' of the horizontal blanking pulse. Its purpose is to synchronize the television receiver's color decoder circuitry, providing a stable frequency and phase reference that allows the chrominance (color) information to be accurately demodulated.

Question 2

A broadcast engineer is troubleshooting a heavily compressed video feed and notices that in scenes with fast motion, the image momentarily breaks up into visible square patterns. What is this type of video artifact called?

Accepted Answer

Macroblocking

Answer

Macroblocking is a common video compression artifact where the image appears to be made up of small squares, especially during fast motion or in complex scenes. It occurs when the video codec, which processes the image in blocks (macroblocks, often 16x16 pixels), does not have a high enough bitrate to accurately represent the detail, forcing it to use a less-detailed representation of the block.

Question 3

Which audio measurement unit is standardized for normalizing broadcast audio levels by taking into account human perception of loudness over time?

Accepted Answer

LUFS

Answer

LUFS (Loudness Units Full Scale), also known as LKFS, is the standard unit for measuring and normalizing audio loudness in broadcast. Unlike peak (dBFS) or voltage (dBu) measurements, LUFS is designed to measure perceived loudness over a period of time, which more closely aligns with human hearing.

Question 4

According to the Nyquist-Shannon sampling theorem, to accurately reproduce an analog audio signal with a maximum frequency of 20 kHz, what is the minimum required sampling rate?

Accepted Answer

Slightly greater than 40 kHz

Answer

The Nyquist-Shannon sampling theorem states that the sampling frequency must be at least twice the highest frequency component of the signal being sampled to avoid aliasing. Therefore, for a 20 kHz audio signal, the sampling rate must be greater than 40 kHz. Standard rates like 44.1 kHz and 48 kHz were chosen to meet this requirement with a practical margin.

Question 5

A technician is setting up a new high-definition video router. A signal labeled as 'SMPTE 292M' is being used. What is the nominal data rate of this HD-SDI signal?

Accepted Answer

1.485 Gbit/s

Answer

The SMPTE 292M standard defines the High-Definition Serial Digital Interface (HD-SDI). This standard specifies a nominal data rate of 1.485 Gbit/s, which is capable of carrying uncompressed high-definition video signals like 720p and 1080i.

(CBT) Certified Broadcast Technologist Practice Test

(CBT) Certified Broadcast Technologist Practice Test

CBT - Certified Broadcast Technologist Audio and Video Signals Questions and Answers