CBT - Certified Broadcast Technologist Audio and Video Signals Questions and Answers — Questions and Answers
Question 1: In an analog NTSC composite video signal, what is the primary function of the colorburst?
- To provide a frequency and phase reference for the chrominance signal. (Correct answer)
- To carry the high-frequency luminance (brightness) details.
- To signal the start of a new video frame (vertical interval).
- To set the black and white reference levels for the picture.
Correct answer: To provide a frequency and phase reference for the chrominance signal.
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?
- Ringing
- Mosquito Noise
- Macroblocking (Correct answer)
- Color Banding
Correct answer: Macroblocking
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?
- dBu
- dBFS
- LUFS (Correct answer)
- VU
Correct answer: LUFS
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?
- 20 kHz
- Slightly greater than 40 kHz (Correct answer)
- 22.05 kHz
- 32 kHz
Correct answer: Slightly greater than 40 kHz
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?
- 270 Mbit/s
- 3 Gbit/s
- 12 Gbit/s
- 1.485 Gbit/s (Correct answer)
Correct answer: 1.485 Gbit/s
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.
Question 6: In a modern broadcast facility, what is the process of combining multiple channels of digital audio with a serial digital interface (SDI) video signal into a single stream called?
- Multiplexing
- Audio Embedding (Correct answer)
- Dolby Encoding
- Time Division
Correct answer: Audio Embedding
Audio embedding is the process of inserting digital audio signals (such as AES/EBU) into the ancillary data space of an SDI video stream. This allows both video and up to 16 channels of audio to be transported over a single coaxial cable, simplifying wiring and ensuring audio and video remain synchronized.
CBT - Certified Broadcast Technologist Audio and Video Signals Questions and Answers
In an analog NTSC composite video signal, what is the primary function of the colorburst?