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Recording Fundamentals

INART 258 Fundamentals of MIDI & Digital AudioMark Ballora, instructor

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Recording Fundamentals

Recall the slides from earlier presentations concerning reverberation...

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Distance

As sound sources move farther from us their volume drops.

Another change that occurs is the ratio of direct sound to reverberant sound.

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Listener

ReverberationSimulates the natural propagation of sound in a closed space, in which wave fronts reflect off of the space’s surfaces. A longer travel path means a short delay before the front reaches the ear.

Three stages:

Direct sound from source to listener; gives the impression of source’s location.

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Early reflections: first reflections to reach listener from surfaces; give the impression of room size.

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Diffuse reverberation: later and more frequent second (and higher)-order reflections, give the impression of the “room’s sound.”

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Reverberation

time

amplitude

Impulse Earlyreflections

Diffuse reverberation

Acousticians measure a room’s impulse response by creating a short sound burst (hand clap, flick of a lighter, click from a toy) and measure the amplitude and timing of the reflections.

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Reverberation

As reverberation is an essential component of natural sounds, it is considered an essential effect in recorded and amplified sounds.

Popular music is recorded one instrument at a time, and then an artificial environment is creating by mixing and adding reverberation (and other effects).

Classical music is recorded in a carefully selected venue, with the intention of capturing the sound of the performer in that space.

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Reverberation and Recording

In concert recording, choices of microphone selection and placement are meant to capture a desirable blend of direct and reverberant sound in the space.

A microphone’s directionality pattern describes the relative intensities it is able to capture from different directions.

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Omnidirectional MicrophonesOmnis capture sound equally from all directions.

This is illustrated on a polar diagram.Imagine the microphone is in the center of the circle.The heavy line indicates that sounds from all directions are captured with equal intensity.

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Directional MicrophonesDirectionals are most sensitive to sounds arriving from a frontward direction, and less sensitive to sounds arriving from the sides or rear.

A directional pattern commonly used in recording is the cardioid, which drops in sensitivity at the sides, and captures very little from the rear.

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Microphone Placement

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Localization vs. Spaciousness

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Localization refers to an ability to recognize apparent locations of performers when listening to a stereo recording. This often relies an the listener sitting in a “sweet spot” equidistant between two speakers, which is not always possible.

Spaciousness refers to a quality of diffuse reverberation. It is apparent to listeners whether or not they are situated in a “sweet spot.”

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Microphone Configurations

Seasoned recording engineers know many varieties of configurations and microphone types.

Different configurations offer advantages in terms of strong localization, spaciousness, and the balance of direct to reverberant sound.

What follows are two “entry level” configurations that are helpful starting points.

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Microphone Configurations

In this configuration, at least two microphones are arranged in an arc around the performers.

Since performers will be closer to one microphone than to another, their instruments’ wavefronts will reach one microphone before another.

These time-of-arrival differences contribute to a strong sense of spaciousness, although localization may not be strong.

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Spaced Omnis

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Microphone Configurations

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Coincident Directionals

In this configuration, two directional microphones are placed in the same location, oriented 90° from each other.

Since they are coincident, the time-of-arrival is the same for all wavefronts, but the intensity differences reaching the two microphones create a strong sense of localization, although the sense of spaciousness may be weak.

In an X-Y configuration, two cardioids are oriented 90° from each other.

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Microphone Configurations

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Semi-coincident Directionals

In this configuration, two directional microphones are slightly spaced.

The distance between them is typically on the order of 7.5”, the average diameter of the human head.

This configuration is a compromise, offering both intensity and time-of-arrival differences, and thus creating a fair sense of both localization and spaciousness.

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Phantom Power

Some microphones require an electrical current to keep them on.

This is typically supplied by the device the microphone is plugged into. This device sends a current up the microphone cable (typically +48V DC) that powers the microphone.

If a microphone does not require phantom power, it will not be affected if the receiving device has phantom power turned on.

However, it is good practice to plug a microphone in before turning on the phantom power, and to turn phantom power off before unplugging a microphone.