CAT CAT Digital Audio and Networking 1 — Questions and Answers
Question 1: What is the Nyquist theorem's requirement for the sample rate relative to the highest audio frequency to be captured?
- The sample rate must be at least twice the highest frequency (Correct answer)
- The sample rate must equal the highest frequency
- The sample rate must be at least 10 times the highest frequency
- The sample rate must be four times the bit depth
Correct answer: The sample rate must be at least twice the highest frequency
The Nyquist theorem states that to accurately reconstruct a signal, the sample rate must be at least twice the highest frequency present in the signal.
Question 2: What does the acronym AES/EBU stand for in professional audio?
- Audio Engineering Society / European Broadcasting Union (Correct answer)
- Analog Encoding Standard / Electronic Broadcast Unit
- Audio Exchange System / Enhanced Balanced Utility
- Automated EQ System / Extended Bandwidth Utility
Correct answer: Audio Engineering Society / European Broadcasting Union
AES/EBU (Audio Engineering Society / European Broadcasting Union) is a standard digital audio interface that carries two channels of digital audio over a balanced 110 Ω XLR cable.
Question 3: Which Dante network audio transport protocol layer does Dante audio primarily operate on?
- Layer 2 (Ethernet) and Layer 3 (IP/UDP) (Correct answer)
- Layer 1 (physical) only
- Layer 7 (application) only
- Layer 4 (TCP) exclusively
Correct answer: Layer 2 (Ethernet) and Layer 3 (IP/UDP)
Dante uses standard Ethernet at Layer 2 for device discovery and Layer 3 UDP/IP for media transport, allowing it to run on standard managed switches.
Question 4: What is jitter in a digital audio system?
- Timing variations in the digital clock that cause audible noise or distortion (Correct answer)
- Quantization error introduced during analog-to-digital conversion
- Packet loss in a networked audio stream
- Aliasing caused by undersampling
Correct answer: Timing variations in the digital clock that cause audible noise or distortion
Jitter is the variation in timing of the digital sampling clock; even small inconsistencies can cause phase noise and distortion in the reconstructed audio signal.
Question 5: What standard sample rate and bit depth is used by the AES67 networked audio interoperability standard?
- 48 kHz / 24-bit (primary reference, with others supported) (Correct answer)
- 44.1 kHz / 16-bit only
- 96 kHz / 32-bit floating point only
- 192 kHz / 24-bit as the only option
Correct answer: 48 kHz / 24-bit (primary reference, with others supported)
AES67 specifies 48 kHz as the primary reference sample rate and supports 16- and 24-bit linear PCM, though 96 kHz is also supported as an option.
Question 6: What does dithering accomplish when reducing bit depth in a digital audio file?
- It adds low-level noise to decorrelate quantization distortion, preserving perceived dynamic range (Correct answer)
- It increases the file's bit depth to prevent truncation errors
- It filters high-frequency content before downsampling
- It compresses the dynamic range to fit the reduced word length
Correct answer: It adds low-level noise to decorrelate quantization distortion, preserving perceived dynamic range
Dithering adds a small amount of shaped noise before truncation so that quantization errors become random (noise) rather than correlated distortion, improving perceived audio quality.
