Audio Systems and Signal Processing
What this domain tests
This domain tests gain structure, impedance, balanced versus unbalanced interfaces, phantom power, digital sampling, and DSP functions such as EQ, delay, limiting, and routing. Items often ask you to identify the correct interface level or calculate a delay or gain change.
Core rules
- Microphone level is typically around −60 dBu, line level is +4 dBu professional or −10 dBV consumer, and loudspeaker level is much higher.
- Balanced connections use two signal conductors plus shield and rely on common-mode rejection; impedance bridging requires the load to be at least about 10 times the source impedance.
- Phantom power is 48 V DC applied common-mode to both signal conductors, normally for condenser microphones; do not apply it to unbalanced or ribbon microphones that are not rated for it.
- Digital audio sampling must exceed twice the highest frequency of interest (Nyquist); 48 kHz sampling supports content up to 24 kHz.
- DSP delay is used for loudspeaker alignment and lip-sync correction; latency must be included in the system budget.
Worked example
A delay loudspeaker is 8.5 m behind the main loudspeaker. Find the delay needed to align it to the main at 20 °C.
- Sound travels about 343 m/s.
- Delay = distance / speed = 8.5 / 343 = 0.02478 s.
- Convert to milliseconds: 0.02478 × 1000 = 24.8 ms. Reasoning: delay is a time calculation, not a level calculation. If the delay loudspeaker is physically behind the main, its signal must be delayed so both arrive together at the listener.
Traps
- Confusing dBu and dBV references, or treating −10 dBV consumer level as equal to +4 dBu.
- Applying phantom power to an unbalanced source or a microphone not rated for it.
- Setting gain structure so the DSP input clips before the amplifier does.
- Forgetting that EQ boosts reduce headroom and can increase feedback risk.
- Ignoring processing latency when aligning audio to video.