100+ Free SBE CEA Practice Questions

Explanation: For voltage (and other amplitude quantities), dB = 20·log10(ratio). Since 20·log10(2) ≈ 6.02 dB, doubling the voltage raises the level by about +6 dB. Doubling power, by contrast, gives +3 dB because power uses 10·log10.

Explanation: 0 dBu references 0.775 V RMS, the voltage that dissipates 1 mW into a 600-ohm load (a legacy of telephone-line practice). The 'u' denotes 'unloaded,' meaning the reference is the voltage itself regardless of actual load impedance.

Explanation: 0 dBV references exactly 1.0 V RMS. The dBV scale is common in consumer equipment, whereas professional gear typically uses dBu (referenced to 0.775 V). The difference between the two references is about 2.2 dB.

Explanation: dBFS means 'decibels relative to full scale.' 0 dBFS is the highest level a digital system can encode; all usable signal levels are negative values below it. Exceeding 0 dBFS produces hard clipping because there are no code values above it.

Explanation: For power, dB = 10·log10(ratio). Because log10(10) = 1, a 10× power increase equals exactly +10 dB. Each additional factor of 10 in power adds another 10 dB.

Explanation: 0 dB SPL is referenced to 20 µPa (20 micropascals), the nominal threshold of human hearing at 1 kHz. SPL uses the 20·log10 form because it is a pressure (amplitude) quantity. A pressure of 1 Pa corresponds to about 94 dB SPL.

Explanation: Wavelength = speed of sound ÷ frequency = 343 m/s ÷ 1000 Hz ≈ 0.343 m. Higher frequencies have shorter wavelengths; lower frequencies have longer ones. This relationship governs acoustic behavior such as diffraction and standing waves.

Explanation: When two identical signals are exactly 180 degrees out of phase, the positive peaks of one align with the negative peaks of the other, causing complete cancellation (destructive interference). This is the basis of phase-cancellation problems and of noise-canceling techniques.

Explanation: Human hearing nominally spans 20 Hz to 20 kHz, though the upper limit decreases with age and noise exposure. This range underlies the choice of a 40 kHz-plus sampling rate (per the Nyquist theorem) for full-bandwidth digital audio.

Explanation: Although +10 dB represents a tenfold increase in acoustic power, the subjective sensation of loudness roughly doubles for each 10 dB increase. By comparison, a 3 dB change is the smallest difference reliably noticed in level, and roughly 1 dB is the threshold of just-noticeable difference under ideal conditions.