Using Pressure and Gradient to Derive Microphone Patterns

Audio Days 2011

Paris

David Josephson

Josephson Engineering, Inc.

Santa Cruz, California

Scalars and Vectors

• nondirectional/pressure/scalar– responds to pressure from any direction

• directional/pressure-gradient/vector– responds to difference in pressure between

two points

Pressure Response

Pressure Response

Pressure Gradient Response

Pressure Gradient Response

Cardioid pattern

+ =

What is B-Format?

• signal format for Ambisonics

• W – omnidirectional (pressure)

• X – figure-8 (cos ) facing front-to-back

• Y – figure 8 facing side-to-side

• Z – figure 8 facing up-to-down

Native B-format

• omnidirectional mic produces W signal

• front-facing bidirectional mic produces X

• side-facing bidirectional mic produces Y

• (optional) up-down mic for Z

Set pattern with ratio of W to X

a + b cos()

a ... is how much of the omni (W)

b ... is how much of the fig-8 (X)

+ =

X + Y = another figure-8 ...pointed at an angle corresponding to the ratio of X and Y

5.1 from B-format

• FC = aW + bX (where a/b sets pattern)

• FL = aW + bX + cY

• FR = aW + bX - cY

• SL = aW - bX + cY

• SR = aW - bX - cY

• LFE = low passed W

Josephson C-700S

W

X

Y

Billy Pitrone – guitar and vocal Sarah Eblin – bass and vocal Pete Hicks – fiddle, mandolin and vocalRob Horgan – banjo

Recorded by Dave Nielsen at Rancho Armadillo, Santa Cruz

www.beancreekbluegrass.com

Anna Clyne, rewind

Cabrillo Music Festival Orchestra, Marin Alsop, director Recorded by Cuco Daglio www.cabrillomusic.org