Fundamentals of Audio and Video Engineering
What this domain tests
The Fundamentals domain tests the physical and perceptual basis of AV work: decibels, power and voltage ratios, inverse-square propagation, wavelength, frequency, timing, and basic human perception. Expect calculation-style items that require you to choose the correct reference and log formula, not just recall a definition.
Core rules
- Power ratios use 10 log10(P2/P1); voltage, SPL, and distance ratios use 20 log10(V2/V1).
- Doubling power adds 3 dB; doubling voltage adds 6 dB; doubling distance from a point source in a free field reduces level by 6 dB.
- Wavelength is λ = c/f. Sound speed is about 343 m/s at 20 °C; light speed is about 3 × 10^8 m/s.
- Human hearing spans roughly 20 Hz to 20 kHz; video frame rates must satisfy motion and flicker perception.
- Keep references straight: dB SPL is referenced to 20 µPa, dBu to 0.775 V, dBV to 1 V, and dBFS to digital full scale.
Worked example
A loudspeaker has sensitivity 90 dB SPL at 1 W/1 m. An amplifier delivers 100 W. Ignoring room gain, find the expected level at 10 m.
- Power gain: 10 log10(100/1) = 20 dB, so the 1 m level is 90 + 20 = 110 dB SPL.
- Distance loss from 1 m to 10 m: 20 log10(10/1) = 20 dB.
- Result: 110 − 20 = 90 dB SPL. The reasoning matters: use 10 log for power, 20 log for distance, and do not apply a blanket 6 dB per metre without checking whether the source is a point source and whether the space is free-field or reverberant.
Traps
- Using 20 log for power ratios or 10 log for voltage ratios.
- Forgetting that inverse-square loss applies to point sources in a free field, not to a diffuse reverberant room.
- Mixing dB SPL, dBu, and dBFS as if they were interchangeable.
- Treating wavelength as independent of frequency.