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Author Topic: Mic cap types and setups  (Read 1873 times)

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Offline Sean Gallemore

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Mic cap types and setups
« on: August 28, 2003, 05:20:10 AM »

nice concise page I found, reference for idiots like me who can't remember it all, they forgot HRTF though ;)

Common Microphone Technology and Setups

    (ideally) even frequency response and sensitivity at any angle.
    Highest sensitivity at 0 and 180 degrees, with maximum drop at 90/270 degrees.
    Highest sensitivity at 0 degrees, and (ideally) no sensitivity at 180, with a linear to exponential transition between both.
    Same as cardoid, with a steeper (log) sensitivity curve - i.e. less sensitivity off-angle.

With real-world directional mics the frequency response is not linear across the directional pattern, especially on more affordable mics - you get what you pay for. And large distance recording with directional microphones is more problematic as they have a proximity effect - i.e. distance relative low frequency response.
Microphony techniques

Individual pickup
    One suitable mono microphone per source. Nearly every professional stage and studio recording is done that way. No stereo ambience at all, staging (if any) done by panning in the mixdown (and eventual reverb processing). Perfect signal for postprocessing and optimum intellegibility, but no real stereo recording. Whenever you do not care about ambience and have the option to install the right microphone on every source, use individual microphones!
A-B (narrow base)
    omni mics at narrow (20-100, typically 50 cm) distance. Stereo image mainly due to time difference between mics. Simple setup, but frequency-dependent obliteration of signals in mono mixdown (poor mono compatibility) and rather limited stereo imaging over spreakers. Good large distance properties. Headphone playback generally better than over speakers.
A-B (wide base)
    omni mics at wide distance. Stereo image is due to intensity difference and large time difference. Good stereo image for ideal speaker playback environments, but unnatural stereo imaging in less-than-perfect playback settings, and extremely artificial over headphones. Often has decent mono compatibility, but may fail especially in rooms with little or no ambience.
    directional mics at the same location, at cross angles. Intensity stereophonics. Good speaker playback and mono compatibility in a small setup. Does better than wide A-B over headphones. Popular system for cheap single-point mics.
    figure-eight at 180 degrees with cardoid at 0 degrees. Intensity based, effectively an electrically generated X-Y with angle variable by mixing. Decays to the cardioid signal on mono (perfect mono compatibility). Somewhat lacking base width for good headphone listening. Popular system for higher-priced single-point mics.
    Omnidirectional capsules at ear distance, separated by (natural or artificial) head. Mainly run-time stereo imaging, with almost natural frequency related intensity due to boundary effects and baffling of the head. Can have perfect headphone quality, but frequency dependent phase obliteration can make it almost useless for broadcast (mono compatibility) and speaker playback.
    Crossed figure-eights, effectively a special X-Y setting with rear-sensitivity. Better separation, but possible frequency obliteration problems with in-phase sound from the rear.

    cardioids at 90 degrees separated by 20 resp. 30 cm. In between X-Y and narrow A-B, somewhat less head-related than ORTF.
    Cardioids at 110 degrees separated by 17 cm. In between X-Y and narrow A-B. Stereo image has sufficient amounts of intensity difference for speaker playback, but still some runtime imaging and suitable mic distance for natural headphone listening. Very good allround setup, but may have some sensitivity gap in the center.
    Narrow A-B at about 20 cm with a "Jecklin disc" baffle. The baffle provides for more intensity separation and more head-like time difference properties. Good both over speakers and headphones, bulky setup.
Pressure Zone Microphones (PZM)
    Basically, an omnidirectional mic mounted on a large flat surface. Utilizes the (usually unwanted) fact that levels increase at surfaces. Properties extremely dependent on the setting, but occasionally handy in wide A-B, as distance to the sound source may have little impact on intensity (given sufficiently hard surfaces). Most common application: Studio round-table.

The "tie-clip" binaurals are really Lavalier-type omnidirectionals and could be used for A-B, OSS, binaural, PZM and individual pickup technologies. The common shoulder-mount setup really is something in between narrow A-B and binaural. For better binaural setups they should be mounted immediately at the ears. There are some cardioid clip-ons about, and shoulder-mounting them ought to result in something close to DIN/NOS/ORTF - haven't tried them yet, but I'd expect them to have more reasonable speaker playback characteristics.

Generally, intensity stereophonic recordings can be mixed and edited, while stereo based on time difference requires absolutely identical settings and environments between recordings for mixing/editing.

For broadcast applications, I'd recommend individual (handheld) cardioid or pin-on microphones whereever possible, especially for interviews. If you do not explicitly want a seasick audience, never use handheld stereo mics, except possibly for brief ambience recordings, taking special care not to move. For all other stereo recordings, use a mic stand, with a M-S single-point for fast recordings. ORTF setups are better if a more complicated fixed installation at close to medium distance is possible. For large distances to the source, use narrow A-B or OSS.

« Last Edit: February 18, 2005, 12:50:07 PM by dmonterisi »


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