Audio Engineering Midterm

YOU BETTER STUDY

What is a microphone?

A transducer

How is a microphone like a speaker?

It’s like a speaker in reverse (TEST)

Parts of a mic

A diaphragm that is stretched over the coil, ribbon, or plates, along with other parts to complete the transducing process

Mic technologies

Magnetic Induction and Variable Capitence

Magnetic Induction(type of mic)

Moving Coil(Dynamic), Ribbon

Variable Capitence(type of mic)

Condenser

Each mic and mic type is a measure of what

Voltage and energy of diapragm

Electromagnetic(dymanic)

Wrap wire around a nail; connect the wires to a volt meter; move it over a magnet and measure voltage / energy.

Dynamic Mic Characteristic(moving coil)

Inexpensive, rugged/sturdy, Least sensitive, Capable of handling high SPL

Popular Dynamic Mics

Shure SM57 / SM58 / SM7B Developed in the 1930’s /UniDyne Sennheiser 421 ElectroVoiceRE-20 / RE-15

Magnetic Induction

The element of a ribbon microphone works much like its own diaphragm. It is made from a thin strip of metal suspended between a magnet. (RCA’s began developing in 1920’s (44))

Ribbon Microphone (magnetic induction)

Electrical signal is measured by how fast the ribbon moves, not how far.

Ribbon Mic traits

uses corrugated, thin ribbon suspended in magnetic field Air Pressure differences between front & back cause it to move

Ribbon Mic characteristics

more fragile, more expensive, more sensitive than moving coil, have a small output level =poor SNR, not used in high SPL situations (high AIR pressure levels), noisy in distant mic situations

Condenser Mics

The element of a condenser microphone contains a diaphragm one fixed

Condenser Mic characteristics

Condenser mics are the only mics that require power, either by batteries, an external power supply, or phantom power: 48VDC, most sensitive, Most expensive, Can Handle High SPL

Phantom Power

Condenser Mics, 48DVC

General Mic Selection Considerations

Proximity Effect

High SPL / Overload

Frequency Response

Signal-to-noise ratio

Harmonic Distortion

Sensitivity

Proximity Effect

increase in LF response when placed near sound source; typical of directional mics

Most sensitive mic

Condenser Mic

Least Sensitive Mic/Most rugged Mic

Moving Coil, Dynamic

Most fragile Mic

Ribbon

How to minimize proximity effect

distance ( > 1 ft.)

Low Freq. roll-off filter

change pattern (omni-directional)

use a“pop filter”to keep singer back

use slightly off-axis

Bass roll-off/High pass

Reduces the low end frequency

rumble

low frequency vibration conducted through adjoining surfaces

How to reduce rumble

shock mount, bass roll off, using a mic with a reduced LF response

Shock mount

wraps around mic to reduce rumble, it keeps it from transmitting to mic, but does not protect mic

Polar/pickup pattern

A microphone’s directiona lsensitivity varies with frequency.

Polar/pickup pattern traits

The Higher the frequency, the more directional a mic becomes.

The lower the frequency, the less directional it becomes regardless of its pickup pattern.

Polar pattern def

a mic’s sensitivity with respect to direction and frequency

uni-directional

Picks up sound primarily in one direction (heart like shape-cardioroid)

omni-directional

picks up sound equally in all directions

bi-directional

equally picks up sound from two opposite directions (figure eight)

hypercardioroid

super—cardioroid

Multiple pattern directional mics

mics that are capable of switching from one pick-up pattern to another

The sound a mic receives is dependent on what

The nature of the sound source

The acoustic environment

The placement of themic

Close mic technique

Dry, more intimate sound

Control Sound Sources

Control Leakage

Allow use of FX later

Distant mic technique

More open acoustic sound

More natural sounding

close” micing (< 3 ft. from source)

aids sound isolation

adds“presence”

minimizes acoustics

little phase cancellation

distant (“distance”) (> 3 ft. from source)

natural blend acoustical space

room tone or ambiance

high probability of phase

On axis

Singing directly into the mic

off axis

A bit off center/roll off the bass a bit

3:1 rule

each mic must be at least 3x farther apart than each is from its source

Stereo micing

is concerned with picking up a sense of left/right stereo imaging...

use of two microphones to obtain a“coherent stereo image

Spaced pair

2 identical mics

Spaced 3-30ft apart

Likely to have phase problems

Coincident(X/Y)

2 identical mics

capsules aligned

angled 90°-135°

minimal phase problems

Near coencident

2 identical mics

elements angled 90°–130°apart

possibility of phase problems

Near coincident ORTF

(2identical mics,“near-coincident”, angle of 110 degrees)

M/S(midside)

2 complimentary mics

1 directional, 1 bi-directional

capsules aligned

minimal“phasing”

Deca tree

uses 3 omnimics

placed in “T” 8-20in. apart

Used in film scoring

Basic techniques

Large Diaphragm mics best suited for capturing low frequency information.

Small best suited for Higher frequencies.

Loudspeaker

the last link of the soundchain.

a device that helps usevaluate the quality ofevery sound

transducer

converts one type of energy (electric) into another type (acoustic)

Types of loudspeakers

Moving-coil (most common)

Ribbon

Electrostatic

Cone(loudspeaker anatomy)

Made of paper or plastic

Basket(loudspeaker anatomy)

Metal frame around the speaker

Voice coil(loudspeaker anatomy)

Electro magnetic coil of wire

Spider(loudspeaker anatomy)

Holds the coil in place

Woofers

Biggest cones

Produce low frequencies

Tweeters

Smallest cones

Produce high frequencies

Crossover frequency

the point where the frequency spectrum is divided into low and high frequencies, and sometimes mid.

Active crossover

when each driver (tweeter, woofer, sub) has its own channel of amplification. This dramatically increases the available power, dynamic range (softest to loudest sounds), and your control of the system’s tonal response over the whole audio spectrum.

Passive crossover

doesn’t need to get hooked up to a power source to work. There are two kinds of passive crossovers: component crossovers that connect between the amplifier and speakers, and in-line crossovers that fit in between the receiver and the amp.

Two way system

If a loudspeaker is divided once

Frequency(judging a loudspeaker)

Just like microphone response curves....We desire a wide response

the measure of an audio system’s ability to reproduce a range of frequencies with the same relative loudness...

Distortion(judging a loudspeaker

IM (intermodulation-two or more frequencies (usually high) combine and create dissonance unrelated to the original signal),

THD (total harmonic distortion-harmonics is added to the signal that were not present in the original signal

Signal in the reproduced sound that was not part of the original (in %)

Output level(judging a speaker)

Good monitors will reproduce clean signal to 110db SPL

Sensitivity(judging a speaker)

Anywhere from 80db to 100db.

On-axis(directly infront of speaker)SPL(in dB) produced at given distance (1m)with given power (1W)

“efficiency”of loudspeaker

Polar response (judging a speaker)

How a loudspeaker focuses sound at the listening position (HORIZONTAL AND VERTICAL DISPERSION)

Harmonic distortion

harmonics in output not present at input

Intermodulation distortion

“combination tones” produced

Overload distortion

signal is louder than the system can handle

Transient distortion

system cannot accurately reproduce rapid ‘attack’

PHANTOM IMAGE (IMPORTANT)

Occurs when you are listening at anequal distance between two speakers.

Center =“free field

+0 dB

Against wall =“half space”

+3 dB

In upper corner =“eighth space”

+9 dB

In corner =“quarter space”

+6 dB

cone motion IN PHASE

sound from two speakers COMBINE

cone motion OUT OF PHASE

sound from two speakers CANCEL

FAR-FIELD MONITORING (IMPORTANT)

Larger, full-range loudspeakers

Typically built into wall

Located several feet from listener

NEAR FIELD MONITORING (IMPORTANT)

Smaller, limited rangeloudspeakers

Set on stands or consolebridge

Located near to listening position (room acoustics do not affect listener)

Surround SOund

designed to envelope the listener in the audio

5:1

5 full range speakers•1 sub woofer (home theaters)

Frequency response in audio is defined as

the measure of an audio system's ability to reproduce a range of frequencies with the same relative loudness.

A "crossover" in a loudspeaker design

divides the frequency range into lows, highs, and sometimes mids, to go to different speakers for reproduction.

In loudspeaker design, tweeters have smaller cones than woofers, and can produce higher frequencies than woofers.

true

The advantage of using loudspeakers to monitor with is that you don't have to worry about the room influencing what you hear.

false

The most common type of loudspeaker is

Moving coil

Mixer

Small•Portable•LimitedPerformance

Console

Larger•Notportable•Provide manyprocessingfunctions•May containcomputer-assistedfunctions

Analog Console

Large, expensive, use lots of power•One knob / switch per function•Sometimes, computer assist withMutes / Levels•Easy to understand

Digital Console

Performance rivaling large analog consoles but with a smaller‘footprint’•Software upgradeable•More complex

Control Surfaces

Integration with Digital AudioWorkstation / DAW•Tactile interface with software•Have all the ‘Look / Feel’ of an analog desk•No audio passing through the desk•Just a Giant sophisticatedMouse!

Why do we need audio consoles

Using multiple microphones•One mic per instrument‘

Adding’ instruments to original recording

‘overdubbing’

Adding ‘processing’ to signal•EQ•Compression, etc.

Separate control of recording & monitoring•recorder•monitors, headphones

BASIC CONSOLE FUNCTIONS

Amplifies•adjusts incoming signal“volume”(‘pre-amp’)

Processes•adjusts 'tone' (EQ) or ‘dynamics’(compressor)

Balances/Blends•“mix” (‘fader’)Combines•“spatial positioning” (‘pan-pot’)

Routes•recorder•effects•monitors, headphones

Signal flow

The path a signal takes to it’s destination..

Pan pot

control that can shift the balance of sound to any point from left to right between two output buses•

allows creation of “stereo image”(spatial positioning)

Signal Processer

A DEVICE THAT ALTERS THE CHARACTERISTIC OF A SOUND.

SIGNAL PROCESSORS ARE GROUPED INTO FOUR CATEGORIES.