Transduction
The kinds of idealized pickups
‐idealized types
‐omni pressure sensitive
‐dipole pressure sensitive
‐dipole velocity sensitive
‐mics with a higher order spatial response
‐sound intensity probes
‐the effects of acoustical mirrors on ideal mics
‐the effects of absorbers on ideal mics
Types of real microphones. Directional response.
‐omni
‐diaphragm dipole
‐cardioid
‐hypercardioid
‐boom mics
‐single transducer mounted on the bottom of an interference tube
‐parabolic reflector models
‐surface mics
‐anemometers
Nonideal transduction in physical microphones
‐electrical operating principles
‐traditional dynamic mics with a magnetic pickup
‐capacitive sensing
‐condensator mics
‐the other model with something solid as the insulator? what was it, now?
‐piezoelectric operation
‐magnetostriction
‐mainly for ultrasound
‐velocity sensitive setups
‐hotwire anemometers
‐ultrasound doppler anemometers
‐typical distortions
‐imperfect frequency response
‐lumped response because of mass
‐vibratory modes in finite size pickups, esp. diaphragms
‐finite size leads to poor low frequency response
‐larger transducers suffer in the high region because the pickup no
longer approximates the ideal infinitesimal pickup for high frequencies
‐reactive sound fields cause coloration when the pickup cannot handle
out‐of‐phase pressure/velocity components equally
‐e.g. the closeness effects, and other nearfield distortions
‐imperfect directional response
‐different efficiency for different frequencies at different angles
‐causes spectral coloring as well
‐interference with the wires, the stands, the cover of the mic etc.
‐high amplitude nonlinearity
‐exhibited by all the devices
‐doppler shift when operating under high transducer displacements
‐inhomogeneity of the magnetic field in dynamic mics
‐inhomogeneity of the electric field in large diaphragm (i.e. large
output) condensator models
‐zero crossing nonlinearity
‐especially with magnetostrictive and anemometer types, where zero
operating conditions are by definition a bit different
‐differential nonlinearity
‐coil winding modulation in dynamic mics
‐inherent nonlinearity of piezo electric pickups
‐hysteresis in magnetostriction
‐noise
‐thermal
‐worst with hotwire anemometers
‐from amplification
‐worst with low output devices
‐the many problems caused by finite output impedance and imperfect
reactance matching
Coincident pairs and multiway mic arrays. Spaced omnis. Spatial recording.
‐Blumlein theory
‐spaced omnis
‐trouble with reactive soundfields
‐sound intensity theory
‐point sources are the ideal, but higher order mics require space to
operate and to be physically possible
‐we need to process the output, we can only approach the ideal setup
Interaction with acoustic spaces
The electronic domain
Pre‐amplification
‐linearity
‐noise
‐switching artifacts
‐extra thermal noise from potentiometers and (possibly) transconductance
amps
Analog to digital
‐slightly more difficult to do than D/A
‐anti‐alias
‐jitter
‐no headroom: with D/A no permanent damage is done if some bits are lost
or if there are artifacts; with A/D the problem permanently affect the
stored sound
‐we have some trouble with the environment of the converters:
EMI
Typical processing at the recording time
‐compression
‐gating
‐correction, compensation and derivation from indirect measurements
‐shuffling
‐equalization
‐e.g. the SoundField microphone
Micing techniques
Coincident pair techniques
‐theoretically ideal when we put rig the sweet spot
‐Blumlein theory!
‐pair
is misleading: we can use anything from mono to multichannel
‐e.g. Ambisonic: full periphony in only 4 channels
‐used for live recordings
‐a sort of purist solution
Mic per source
‐optimized for for post‐production and heavy processing
‐also used to balance disparate instrument volumes in PA apps
‐e.g. horn vs. sitar
‐trouble with source separation and comb filtering defects
Instrumental micing
‐contact mics
‐real sterile, no space
‐common when effects, post‐processing or extreme amplification is
necessary
‐e.g. in almost all pop
‐the electric guitar is a concept, an instrument in its own right
‐drum micing
Harvesting the ambience
‐separate ambience pickups
‐often spaced omnis at the rear of a hall
‐used for decorrelation
‐comb filtering trouble with direct sound leak
Monitoring
‐phones vs. near field vs. full blown speakers
‐the effect is very different
‐phones interfere with the natural feedback for the player
‐mono and stereo compatibility
‐it is difficult to render the stuff plausibly to the player
‐multiple speaker monitoring
‐trouble with feedback elimination
‐movie production differences
‐a lot more offline processing, and stuff having to do with image/audio
synchronization
‐often post‐production/double tracking oriented, instead of overtake like
with common music production
‐the sonic material is more varied, and multichannel production plays a
bigger part