CEA CEA Signal Processing & Electronics 2 — Questions and Answers
Question 1: What is the function of a phase-locked loop (PLL) in digital audio clock systems?
- To convert analog signals to digital
- To lock a local clock to an incoming reference signal for synchronization (Correct answer)
- To measure signal latency
- To generate test tones
Correct answer: To lock a local clock to an incoming reference signal for synchronization
A PLL generates a local clock signal that precisely tracks an external reference, maintaining synchronization and minimizing jitter in digital audio systems.
Question 2: What is 'slew rate' in the context of operational amplifiers used in audio circuits?
- The maximum voltage gain at DC
- The maximum rate of change of output voltage, typically expressed in V/µs (Correct answer)
- The input noise density
- The open-loop bandwidth at unity gain
Correct answer: The maximum rate of change of output voltage, typically expressed in V/µs
Slew rate describes how fast an op-amp's output can change voltage, and if it is too slow for the signal frequency, it causes slew-rate distortion.
Question 3: What is the primary purpose of a de-esser in audio signal processing?
- To remove low-frequency rumble from vocal tracks
- To selectively reduce excessive sibilance ('s' and 'sh' sounds) in vocal recordings (Correct answer)
- To add harmonic brightness to a vocal signal
- To control the dynamic range of an entire mix
Correct answer: To selectively reduce excessive sibilance ('s' and 'sh' sounds) in vocal recordings
A de-esser is a frequency-selective compressor that detects and attenuates harsh high-frequency sibilant energy in vocal recordings.
Question 4: In digital audio, what does 'jitter' refer to?
- Unwanted tremolo applied to a signal
- Timing variations in a digital clock signal that can cause sampling errors (Correct answer)
- The aliasing produced by a low sample rate
- Quantization noise at low signal levels
Correct answer: Timing variations in a digital clock signal that can cause sampling errors
Jitter is the deviation of a digital clock's transitions from their ideal timing positions, which can introduce noise and distortion in digital audio systems.
Question 5: What is the standard impedance of a professional balanced line-level output in audio?
- 600 Ω
- 10 kΩ
- 50–200 Ω (low impedance) (Correct answer)
- 100 kΩ
Correct answer: 50–200 Ω (low impedance)
Professional balanced outputs use low source impedance (typically 50–200 Ω) so they can drive long cable runs with minimal signal loss and noise pickup.
Question 6: What does 'headroom' mean in audio electronics?
- The physical space above the speaker cabinet
- The difference between the nominal operating level and the maximum level before clipping (Correct answer)
- The frequency range above 10 kHz
- The delay time before a compressor engages
Correct answer: The difference between the nominal operating level and the maximum level before clipping
Headroom is the margin between the normal average operating level and the clipping point, allowing transient peaks to pass without distortion.
CEA CEA Signal Processing & Electronics 2
What is the function of a phase-locked loop (PLL) in digital audio clock systems?