Stereo

• Must have two independent channels
• Space, depth, dimensionality = Immersive
• Triangulation of our senses with an object (sight or sound)
• The real magic happens in the brain, not the technology

Visual Stereopsis

Are the images identical?

Psychoacoustics

• A psychoacoustic effect that makes a sound source appear where there is no speaker.

• Differences between two mics/speakers create a left/right stereo soundstage.

• Imaging is the term used to describe how a recording uses the soundstage– space and depth; it is another specific aspect to listen for.

• Localization = How precisely the brain can pin-point where a sound is coming from.

Psychoacoustics

The Phantom Image

Orchestra

Narrow
(mics too close together)

Wide
(mics too far apart)

Psychoacoustics

• Amazingly complex!

• Localization = How precisely the brain can pin-point where a sound is coming from

How We Hear Direction

Psychoacoustics

Headphones...

Intensity Stereo

Sound arrives at exactly the same time at each mic, but at different amplitudes.

Coincident Mic Setups

X/Y:
2 Cardioids @ 90-degrees

Two identical mics as close together as possible.

X/Y:
2 Cardioids @ 90-degrees

X/Y:
2 Cardioids @ 90-degrees

X/Y:
2 Cardioids @ 90-degrees

Blumlein
2 Bidirectionals @ 90-degrees

Blumlein
2 Bidirectionals @ 90-degrees

Intensity Stereo

• Good imaging in many different situations
• Undramatic stereo spread (but can still have a nice soundstage)
• Can be a little "flat" sounding sometimes, but minimizes room sound
• Best mono compatibility (no phase problems, as sound has the same arrival-time at each mic)

Characteristics

Sound arrives at exactly the same time at each mic, but at different amplitudes.

Time-of-Arrival Stereo

Sound arrives at about the same amplitude, but slightly different times at each mic.

• When the ear hears two sounds at the same loudness very close together (within about 30 ms), the brain interprets them as a single sound, coming from the direction heard first.
• The difference between a sound imaging in the center of the soundstage vs. imaging from the side depends on which got to the ear first.

The Precedence Effect

The Precedence Effect

Spaced Mic Setups

A/B:
2 Omnis Spaced According the the 3:1 Rule

A/B:
2 Omnis Spaced According the the 3:1 Rule

A/B:
2 Omnis Spaced According the the 3:1 Rule

A/B:
2 Omnis Spaced According the the 3:1 Rule

A/B:
2 Omnis Spaced for Larger Groups

Time-of-Arrival Stereo

• Preferred for larger groups in better rooms

• Less precise localization, but best overall blend

• Widest stereo spread & most depth

• Potential for mono-compatibility problems, as sound arrives with different phase at each mic

Characteristics

Sound arrives at about the same amplitude, but slightly different times at each mic.

Near-Coincident Mic Setups