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