1. 3-D Sound and Spatial Audio MUS_TECH 348

2. Environmental Acoustics, Perception and Audio Processing: Envelopment

3. Envelopment Griesinger “Objective Measures of Spaciousness and Envelopment” Terminology: Spaciousness and envelopment should be taken as identical in meaning. Apparent Source Width (ASW) should be disassociated from spaciousness. Spatial Impression (SI) does seem to capture spaciousness.

4. Envelopment Objective Measures of Spaciousness: Barron’s ratio of lateral energy to total energy (LF or Lateral Fraction) doesn’t work in general environments The ratio measured at a standard distance (LG or Lateral Hall Gain) reflecting the absolute level of the lateral energy is better. Interaural Cross Correlation (IACC) is the best predictor of ASW, but IACC doesn’t work for frequencies below 300 Hz (where it approaches 1.0). Griesinger suggests InterAural Difference (IAD), ratio in dB between the square of the interaural difference signals and the sum of the squares of the individual ear signals.

5. But, envelopment also produced by fluctuations in ITD and IID. This is what the lateral reflections cause and why IACC doesn’t work to predict envelopment for low frequencies! Envelopment

6. Other facts: Fluctuations in ITD and IID below 2000 Hz cause envelopment Fluctuations after 160 ms of direct sound are most effective For sounds below 700 Hz optimal sound envelopment comes from sound arriving at 90-degrees and the optimal angle for higher frequencies moves toward the medial plane. Above 2000 Hz rear locations cause more envelopment; 150-degrees (+/- 30-degrees from rear) is optimal.

7. Three types of envelopment: Continuous Spatial Impression (CSI) - lateral reflections interfere with continuous source sound (delay > 10 ms) Early Spatial Impression (ESI) - lateral energy arriving with 50 ms of the end of an impulsive sound; affects the source more than giving envelopment. Background Spatial Impression (BSI) - when the source is a series of notes diffuse energy arriving after 150 ms creates envelopment; depends on absolute level. Envelopment

8. Three types of envelopment: Continuous Spatial Impression (CSI) Early Spatial Impression (ESI) Background Spatial Impression (BSI) Envelopment

9. William Martens “Are Two Subwoofers Better Than One?” Negative cross correlation indexes reveal the most difference: Light grey - one subwoofer Dark grey - two subwoofers Envelopment

10. MDS analysis of subject comparisons produces two significant dimensions. Dimension 1 relates to image distance and dimension 2 to image width. Envelopment

11. Forced-choice judgments demonstration the dominance of two- subwoofer reproduction for width and intimacy. Envelopment