Cabling, Studio, Acoustics,

Monitoring, Hum, etc

Balanced Lines Two conductors WITH third neutral ground wire

Normally the tip is hot (+), ring cold (-) and sleeve is shield (ground).

Less susceptible to noise

XLR, TRS (tip, ring, sleeve) 1/4”, TT

XLR TRS

Balanced Lines

TT Cable

Unbalanced Lines

2 conductors , NO separate ground

More susceptible to noise

TS (tip and sleeve)=¼” guitar plug, RCA, etc

TS (no ring) RCA

Balanced and

unbalanced

lines - analog

Digital

connectors

Cabling and gear

Balanced gear--->balanced cable--->balanced gear = balanced connection

Balanced gear-->balanced cable--->unbalanced gear = unbalanced connection

Balanced gear-->unbalanced cable--->balanced gear = unbalanced connection

unbalanced gear-->balanced cable--->unbalanced gear = unbalanced connection

Line Level vs. Mic Level

Line level

Consumer (-10 dB)

Professional (+4 dB)

Mic level (-50 dB)

Line Level vs. Mic Level

Low level transducers –mic level (need to be preamped)

Microphones

Magnetic pickups

Tape heads

Phonograph cartridge

Line level transducers – line level (already preamped)

DAC/Tape decks

Optical (motion picture film)

CD & MiniCD

Keyboard

Tone generator

Computer

Cabling – Other Common Types

Cabling – Direct Box We can make an unbalanced line into a balanced line with

use of a direct box.

Instruments that have unbalanced, high impedance outputs

Bass (direct)

Electric Guitar (direct)

Keyboard/Synth

Drum Machine

A direct box:

1) Converts a high impedance unbalanced audio signal into a low impedance balanced audio signal

2) Isolates audio signals electrically (reducing chance of ground loop)

3) Changes line level to mic level input for console

Studio Acoustics

Things to consider when building a control or tracking room

Acoustic isolation – keep external noises out

Frequency balance – room should not alter original recording

Acoustic seperation – no bleed between instruments or control room

Controlled Reflections - how much natural reverberation

Cost

Studio AcousticsTypes

Home/Project Studio

Professional Studio

Room Treatment

Transmission loss- the reduction of a sound signal (in dB) as it passes through an acoustic barrier

The thicker and denser the material, the less the transmission

Bass frequencies are last to be blocked. Why?

Studio AcousticsCONSTRUCTION

Walls – build a “wall within a wall” – studs don’t touch

Floors – floating floors – neoprene mounts

Ceilings – false ceilings with Z channels

Doors – double door/soundlock

Walls & Floor/Ceiling – must not be parallel. Why?

Standing waves worst in a cubical room

Studio Acoustics

Iso rooms/booths –small sealed rooms

Baffles/Gobos – moveable, blankets, etc.

Both prevent leakage/bleed/spill

Wall diffusers – reflect sound

Wall absorbers – absorb sound

High frequencies are absorbed by dense porous materials such as carpet, cloth, etc. 800Hz and up

Low frequencies harder to control - damped by pliable materials – bass traps, 3 main types

Baffle Bass Trap

Studio AcousticsHow do we minimize room reverb?

How would you set up a session with several players in one large room?

Close miking, directional mikes, DI’s,

Characteristics of studios

1930’s-60’s all instruments tracked in one room, room sounds taken advantage of

1970’s/early 80’s – no absorbtion in rooms, dead and dry

Tuning a Room

1. Pink Noise

2. Real-Time Analyzer

3. Graphic Equalizer

Studio Monitors

Studio speakers (otherwise known as monitors) are

transducers that change electrical energy into acoustic

energy, The actual transducer is called a driver

Like microphones, monitors can be classified according

to which type of transducer they contain

Moving Coil (Coil)

Ribbon

Capacitor (Electro-static)

Studio MonitorsSOME TIPS

You can only mix as well as your playback system

Accurate speakers with flat frequency response – my monitor story

Test on a Boombox too, why?

Nearfield monitors – hear direct sound of speakers, no room characteristics

Powered vs unpowered

Speakers on stands – bass properties

Off axis response – 2 people listening together. Where should the listener be?

Control room should have same amt of reverb as house

Different methods of monitoring

Ports

Ports = holes

Ported speakers allow reinforcement of bass frequencies to reflect internally and then emerge from the speaker in an enhanced state.

Un-ported speakers allow no direct exchange of internal speaker air to external; called air suspension speakers.

Speaker Systems

Two-Way System

Each of two speaker cabinets contains two speakers, one

tweeter and one woofer

Tweeter = high frequencies

Woofer = low frequencies

(In a three-way system, each cabinet would contain two tweeters

and one woofer)

Crossovers

When a speaker system contains multiple speakers, it is necessary to split the signal by frequency and send higher frequencies to the tweeter and lower frequencies to the woofer

Out-Of-Phase Speakers

When one lead (wire) is switched on one of the speaker cabinets and causes stereo speakers to compete with each other.

While one speaker is experiencing compression the other is rarefacting and vice-versa.

Results in loss of volume and stereo imaging (can cause insanity).

Speaker Characteristics

Frequency Response

Linearity

Sensitivity

Distortion

Power supply

Problems with power

Voltage “sags”

Power being fed to your studio is not constant, it has dips

With power conditioning device spikes and surges can be clamped

Voltage regulator – 120 v constant

How can we prevent dirty AC power?

Avoid light dimmers

Use power conditioner

Use balanced AC power supply

Hum Prevention

60 cycle or 60Hz hum – caused by electrostatic/electromagnetic interference.

Caused by:

1) Poor cable shields (foil or wires wrapped around main line, must be grounded)--prevent 60 cycle hum as well as RFI.

2) Cables bunched together or power lines in wall and audio cables.

3) No ground

Ground – signal always wants to go to the ground (i.e. getting shocked by mic stand)

Example 3 wire power cord

Hum Prevention

Ground loops – another variation

Ground loops generally occur when there is a difference in potential between the various

grounding points in studio. When potentials like this occur, 60 Hz ground currents and high

frequency noise can flow around the system and cause hum in both audio and video signals.

To avoid:

Use transformer isolated box

Connect everything to same ground

Break the loop (cut ground between 2 instruments)

Hum Prevention/Power

More ways to prevent hum:

Avoid fluorescent lights

Keep cables away from power amps, computer monitors.

Separate power cords/extension cords from other cables

by 1 ft.

Do not coil AC cords.