Sound recording

Common requirements for quality recording

Some scenarios—where would we want to capture sound?

In‐studio sessions

Live, staged performances

Recording in the wild


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.

 ‐diaphragm dipole
 ‐boom mics
  ‐single transducer mounted on the bottom of an interference tube
 ‐parabolic reflector models
 ‐surface mics

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
   ‐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
    ‐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


 ‐switching artifacts
 ‐extra thermal noise from potentiometers and (possibly) transconductance

Analog to digital

 ‐slightly more difficult to do than D/A
 ‐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:

Typical processing at the recording time

 ‐correction, compensation and derivation from indirect measurements
  ‐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
  ‐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


 ‐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
  ‐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