3-D Sound and Spatial Audio

MUS_TECH 348

Stereo Loudspeaker Reproduction

Intensity Stereo

Side Image

Intensity Stereo

Center Image

Typical Pop/Rock and Classical Spatial Distribution

Off-Center Listening

“Precedence Effect”

Mono Compatibility

Why can’t we just reproduce binaural recordings over loudspeakers?

Binaural Recording with Loudspeaker Reproduction

Stereo Loudspeaker Reproduction Creates Notch at 2kHz

How to Eliminate Crosstalk?1) Use a baffle

2) Use out-of-phase signals

180° Out of Phase Signals

180° Out of Phase Loudspeakers

Alternatively

How to make Loudspeaker Reproduction Transparent?

3) Crosstalk Cancellation from Manfred Schroeder (late 1950s)

• Exact Solution

• Make loudspeaker listening more like headphones

• All sounds externalized

Schroeder’s Cross-talk Cancellation System

Schroeder’s Cross-talk Cancellation System

One Step at a Time: Equalization of Loudspeaker Response

EQ Filter

Result

But…

Introduce cross-talk cancellation signal:

But…

There is crosstalkfor the crosstalkcancellation signal!

Full Cross-talk Cancellation Solution:

“Sweet Spot”

The Problems?1. Off-center positions. Only one sweet spot.

2. Individual Differences. Listener’s HRTFs, including H30 and H330, don’t match.

3. High frequency cancellation. Wave lengths are so short that very slight shifts in position throw everything off.

4. 1/H30. Inverting the notches creates big peaks that probably don’t match the listener.

5. Room Acoustics. Indirection sound reaches the listener.

Off-Center Seating in Larger Spaces

Good Each seating position has unique time of arrival delay and level differences. Only the center seats can provide spatial imagery.

Off-Center Seating in Larger Spaces

The separation of the stereo loudspeakers creates different ranges of differences for time of arrival delay.

Off-Center Seating in Larger Spaces

Delayed signal from loudspeaker can create a wide range of subjective impressions!

Off-Center Seating in Larger Spaces

The range of time of arrival delays for typical loudspeaker separatations puts the delay in the range of these different subjective impressions

Loudspeaker Reproduction in Natural Environments

Loudspeakers themselves create indirect sound.

Frequency and Time Response of Loudspeaker in an Empty Room

Impulse response and amplitude response from the loudspeaker to the listener in an empty test room.

Figure 2 shows change with a few absorption panels in place.

More,

Figure 6 finally shows a rooms with only slight indirect sound between the loudspeaker and the listener.

Figure 6 impulse response and amplitude response.