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Monday, November 21, 2011

Sound Engineering

To understand how to record sound you must understand what sound is, what it looks like and how it reacts in an environment.
Acoustics is the study of sound.
Sound is generated by an object vibrating or causing a transient disturbance in air in the human hearing range.
This vibration pushes and pulls air molecules from around the object in all directions (omni-directional).
So sound is a series of compressed and expanded air molecules forming waves in the air.
The complexity of these vibrations caused by its physical design is known as its timbre.
The repetition of these waves is known as its frequency, measured in Hertz.
Sound travels at approximately 1130 ft. per second 770 mph in air. It will travel faster in denser materials, slower in less dense materials.
The frequency range of the human ear is from 20 HZ to 20,000 HZ but average will be approximately 30HZ to 15,000HZ.
The amount of molecules being compressed in the air and expanded is known as its sound pressure level (SPL) measured in Decibels dB.
The range of SPL for the human ear is from the threshold of hearing, 0dB, to the threshold of pain, 140dB.
The proper listening level for mixing and the flattest response for human hearing is from 80dB to 90dB.
The surfaces in an air space cause reflection, absorption and diffusion which creates complex wave patterns and resonances (the over excitement of certain frequencies) due to the interaction and intersection of these waves at various SPL.
This causes what is known as early reflection, echoes and reverberation
  • the higher the frequency, the more direct the sound waves.
  • the lower the frequency the more omni-directional the sound waves.
The best listening environment will be a space with symmetry and the right amount of direct sound (directly from the sound source), reflection, absorption and diffusion to make sure that frequencies and resonance are flat (all frequencies represented equally) at various SPL.
Protect your ears from high or prolonged SPL.

A device that changes one form of energy into another is called a transducer. Example: A Microphone changes sound waves into electrical current when those sound waves move its diaphragm in and out. Our ears are microphones.

Basically we use two types of microphones in the studio: Condensers and Dynamic microphones.

Dynamic Microphones generate electrical current by moving a coil or a metal ribbon through a magnet’s magnetic field (electromagnetic induction). This generates an electrical representation of the sound wave that is hitting its Mylar diaphragm. Because the coil and magnet configuration resist movement somewhat, they are slower with a less frequency response on the high end of the audio spectrum then the condenser microphones.

Condenser Microphones must be powered by a power source like a battery or a 48VDC voltage such as Phantom Power to power its internal preamp. They are more sensitive. They are less rugged by design then dynamic microphones. They have a faster and higher frequency response of the audio spectrum then dynamic mics. Condensers Microphones use the electrostatic principles to generate an electrical representation of a sound wave. When sound waves hit its diaphragm it slightly changes the space between two plates.  With these changes in the space between a negative and a positive plate in the capsule, an electrical current variation is amplified by the microphone’s preamp.

Microphone Patterns
 We basically use two microphone pick up patterns: Omni (from all sides) and Uni-Directional (a Cardioid pattern     from one direction)
Other variations of the uni-directional pattern are the: Figure 8, Hyper-Cardioid, Super-cardiod and Hemispherical. Uni-directional microphones also exhibit an effect known as the proximity effect. This increase in its low frequency response is from 0 to 6 inches away from the mic. It can be flattened out by a bass roll off switch or a high pass filter (HPF) on the microphone or on a mixing console. Another switch that maybe found on some microphones is an attenuation switch. This lowers the signal level coming from the output of the microphone usually 10 to 20 dB. It allows the microphone to capture higher SPL without distorting the microphone or the preamp in which it is plugged into.

Monitor Speakers
Speakers are transducers. They change electrical current to sound wave energy.
Speakers are dynamic transducers.
Monitor Speakers should have a flat response and should be placed in an equilateral triangle from the speaker to listener.
Monitor speakers should be listened to at a moderate level, 80 to 90 dB when mixing.
Example: Our mouths are speakers or sound sources.

Audio Input and Output Levels
Line level (-10db and +4db)
Microphone level
Speaker level

3 types of audio transmition line cables:
  • Balanced, low impedance (3 conductor, XLR and TRS (Tip, Ring, Sleeve) ¼ inch connector)
  • Unbalanced, high impedance (2 conductor, TS (Tip, Sleeve) 1/4, 1/8 inch plug)
  • Insert cable Unbalanced, high impedance (2 conductor, TS , (Tip (send), Ring ( Receive) and Sleeve Ground)
       ¼ inch plug
  • Speaker cable (unbalanced)

Pre-Amplifiers and Amplifier
Makes a signal level louder or isolate audio signals from one another.

Mixing Consoles   (Analog and Digital)
An electronic device that blends, routes and amplifies audio signals
A mixer is used to:
·         amplify and adjust signal levels (trim and faders)
·         mute or channel-on switches
·         equalize (EQ) and filtering effects
·         Solo listen (PFL or AFL)  (pre-fader listen and after fader listen) of an individual channel
·         Pan Pots are spatial perception controls (panning from left to right)
·         routing audio signals to buss lines for Time based effects processing, auxiliary sends, monitoring and groupings
·         inserts as a break-in point for routing to Dynamic and Equalizing effects.

Basically two types of effects used in auxiliary buss sends:
  • Time based (Delay, Reverb, Flanger, Phaser)
  • Pitch based (Harmonizing, Chorus, Octave divider)
In addition, modulation is used to affect its intensity and sometimes change one effect to another.
(Modulation changes one of the key components of the effect such as time or phase at a certain pace.)

Basically two types of insert (inline) effects:
  • Dynamic effects (Compression and Expansion)
  • Frequency effects (Equalizing)

Recorders and Recording Software
  • Analog (tape) Editing Type: Linear
  • Digital (digital tape, hard drive and flash) Editing Type: Linear and non- linear
Plug-ins are added effects to a host or native computer recording software.

The Recording Process
Preparing for a session
Studio protocol, session procedure, communication and etiquette
Basic Tracks
Editing copy/paste
Adding effects

Jobs in audio market:
Studio, Live, Theater, Music production, TV and Radio, Audio for video, The Web, Corporate, Clubs, Sale, Rental, Touring Roadie, Amusement and Theme Parks, Transfer or Restoration, Teaching, Home or self recording, consulting, Musician, Acoustic Engineer, Programmer, Designer, Private contractor, Installer.

1 Basic Sound Reinforcement?    1 session
The mixer
Mains FOH
Submixing grouping
Aux Sends effects and monitors
Cables, stands and accesories
Set up & procedure
Running the show
Tear down

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