⚙️ ENGINEER LEVEL: Psychoacoustic Optimization
Critical Bands and Auditory Masking
Human hearing resolves frequency using critical bands — roughly constant-Q filters in the cochlea. The bandwidth of these critical bands increases with frequency.
Critical bandwidth approximation:
CBW = 25 + 75 × [1 + 1.4 × (f/1000)²]^0.69 [in Hz]
At 100 Hz: CBW ≈ 100 Hz
At 1000 Hz: CBW ≈ 160 Hz
At 10000 Hz: CBW ≈ 2500 Hz
Implications for EQ:
Parametric EQ filters should match critical bandwidth: - At 60 Hz: Q ≈ 0.6 (wide) - At 1 kHz: Q ≈ 6.3 (narrow) - At 10 kHz: Q ≈ 4.0 (wider again)
Using constant Q across all frequencies (e.g., Q=2.0 everywhere) wastes resolution at low frequencies and over-corrects at high frequencies.
Optimal EQ filter placement uses critical-band-matched Q values for each center frequency. Dirac Live and other advanced room correction algorithms do this automatically.
Precedence Effect (Haas Effect) and Image Manipulation
When two identical sounds arrive within 1–30 ms of each other, the brain perceives them as a single sound coming from the direction of the first arrival.
Application to car audio:
Even if the left speaker is louder by 10 dB, if the right speaker's sound arrives 1 ms earlier, the image shifts right.
Using time alignment to elevate image:
If tweeters are mounted low (door level), delaying them slightly relative to midbass causes the midbass to arrive first at some frequencies. The brain localizes the sound higher (midbass location) even though the tweeter provides high-frequency content.
Practical implementation:
- Mount tweeter high (A-pillar)
- Mount midbass low (door)
- Time-align both to listener
- Fine-tune: delay tweeter by +0.3 to +0.6 ms beyond perfect alignment
- Image elevates — vocals appear at dashboard height or above
This is a subtle manipulation but highly effective in SQ competition.