# Using Pressure and Gradient to Derive Microphone Patterns Audio Days 2011 Paris David Josephson Josephson Engineering, Inc. Santa Cruz, California.

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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

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

Soundfield B-format process Four subcardioid capsules in tetrahedral array (LFU, LBD, RBU, RFD) W = LFU + LBD + RBU + RFD X = - LFU + LBD + RBU - RFD Y = - LFU - LBD + RBU + RFD Z = - LFU + LBD - RBU + RFD (Craven and Gerzon 1974, scaling and equalization omitted)

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 vocal Rob 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

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