1. 3-D Sound and Spatial Audio MUS_TECH 348

2. Cathedral / Concert Hall / Theater Sound Altar / Stage / Screen Spiritual / Emotional World Subjective Music Ambience Cultural Context of Spaciousness

3. Environmental Acoustics, Perception, and Audio Applications

4. Distance Perception We already discussed that Chowning makes use of the fact that in very reverberant environments like concert halls, perceived distance varies in proportion to indirect/direct sound ratio. The absolute sound intensity and the relative sound intensity (changing as 1/distance) are cues in themselves.

5. Distance Perception Most environments have little or no reverberation in the way we discuss it in concert halls. In these environments, changes in distance can be cued by changes in the timing of low- order reflections. Consider too,

6. Distance Perception Most important is the time interval of the initial gap between the sound and first- order reflections. For example, as a sound moves farther away, the gap becomes smaller.

7. Distance Perception We know that distance judgments can be influenced by sound intensity, relative intensity, HRTFs, the indirect-to- direct energy ratio, and the timing of first-order reflections. In addition, distance judgments can be influenced by cognitive factors like knowledge of the sound source or likely distances given the context. It seems that distance judgment is multi-faceted.

8. Position Perception Early reflections also constitute an element of realism for simulated acoustic spaces independent of distance perception.

9. The kind of interaural decorrelation of that is experienced in concert hall reverberation is an important aspect of audio applications. Interaural decorrelation can be created in a variety of ways. Decorrelation Revisited

10. Multichannel Reverb Reverb L R Stereo reverb units produce output channels that are uncorrelated in order for the listener to experience some degree of spaciousness. uncorrelated outputs Pro Audio Decorrelation

11. Decorrelation by Reverb Reverb L R Pro Audio Decorrelation Stereo reverb is typically used in combination with the source signal. diffuse field

12. Decorrelation by Detuning Pitch Shift L R Pro Audio Decorrelation A related spatial effect somewhere between spatially diffuse reverberation and dual images can be created by detuning one channnel.

13. Studio Decorrelation by Recording Record the same performance twice Put one on left and one on right Pro Audio Decorrelation Recording a performance twice creates similar dual image effect.

14. The degree of perceived ‘spaciousness’ and the effectiveness of many of these effects are predicted by level of interaural decorrelation. The objective measure of correlation (and decorrelation) is the cross-correlation measure, Ω(∆t), and the cross-correlation index (peak of the cross-correlation measure). Decorrelation in Audio where ∆t represents a temporal offset between y 1 (t) and y 2 (t).

15. Examples of correlation measure: Decorrelation in Audio

16. Five Effects of Decorrelation on Stereo Imagery 1. the timbral coloration and combing associated with constructive and destructive interference of multiple delayed signals is perceptually eliminated, 2. decorrelated channels of sound produce diffuse sound fields (akin to the late field of reverberant concert halls), 3. decorrelated channels produce externalization in headphone reproduction, 4. the position of the sound field does not undergo image shift with changes in the position of the listener relative to stereo loudspeakers, 5. the precedence effect which causes the collapse of the image into the nearest loudspeaker is defeated enabling one to present the same sound signal from multiple loudspeakers. Decorrelation in Audio

17. Effect #1 the timbral coloration and combing associated with constructive and destructive interference of multiple delayed signals is perceptually eliminated

18. Decorrelation in Audio Effect #2 decorrelated channels of sound produce diffuse sound fields (akin to the late field of reverberant concert halls),

19. Decorrelation in Audio Effect #3 decorrelated channels produce externalization in headphone reproduction

20. Decorrelation in Audio Effect #4 the position of the sound field does not undergo image shift with changes in the position of the listener relative to stereo loudspeakers

21. Decorrelation in Audio Effect #4

22. Decorrelation in Audio Effect #5 the precedence effect which causes the collapse of the image into the nearest loudspeaker is defeated enabling one to present the same sound signal from multiple loudspeakers

23. Decorrelation in Audio Effect #5

24. Decorrelation in Audio

25. Another Distance Effect A constant phase offset (rather than cross-correlation index) creates an impression of changing image distance. Like HRTF reproduction, this distance effect depends on how close the listener is to the sweet spot.