Chapter 5: Projection & Audio

Inverse Square Law

Since the same amount of energy is spread over an increasing area, the intensity of light must decrease.

Keystone Distortion

Caused by the projector being anywhere other than directly perpendicular to the absolute center of the projection surface.

Hotspot

Seeing the light from the projector through the surface.

ANSI Lumens

A unit of measure for the amount of light a projector is able to produce.

Pixel

The individual dots that make up a projected image.

Resolution

The number of "pixels" an image contains or a projector is capable of producing.

Aspect Ratio

Of an image describes the proportional relationship between its width and its height.

Front Projection

Advantages: no need for space upstage of screen and no crossover problems.

Disadvantages: Projector placement (Keystoning) and Image on dancers, dancers shadows on the screen.

Front Projection Surface

Projection surface:

Advantages: Highly reflective projection surface capable of brighter, sharper images.

Disadvantages: Will not disappear and go to black, Needs an image or color on it almost all of the time.

Rear Projection

Advantages: Placement (Can be centered on an axis perpendicular to the center of the projection surface if you have enough depth).

Disadvantages: Can cause crossover problems and needs a lot of space upstage/behind the projection screen.

Rear Projection Surface

Projection surface: Professional screens transmit clean, crisp images while eliminating the hotspot. The screen retransmits the light.

Advantages: Comes in a variety of shades from white to black. Can be placed behind a black scrim to transition between black and projected image backgrounds. Can be used very effectively as a skydrop. Affected less by ambient light.

Disadvantages: On cheap screens, you can see the projector through the screen (hotspot). With most modern professional screens, you do not. Cheaper screens and heat-welded seams. Can be used slightly less effectively when used as a front projection surface. Expensive

How is projector brightness/intensity measured?

Projector brightness or intensity is measured in number of lumens produced by the projector.

Displays - Not Projections

Displays are electronic devices that display images on their screens or surfaces via light producing dots or pixels, like your television or computer monitor. The images are not projected through the air and onto a screen. They are emitted from the screen.

Frame Rate

The number of images per second.

Compression

Compression. We compress files to make them smaller, so they can be uploaded and viewed for the best experience, quality vs ease of use.

Compression is achieved in different ways, but basically by software that instead of storing each individual frame of a video, sets key frames and then compares the next image or frame to that key frame, and only stores what changes.

Artifacts

Blocky pieces of image that are the result of the keyframe not being updated correctly.

Video Codec

A type of compression scheme designed for the intended use of the video.

Color Depth

Roughly how detailed you are about the difference in color.

Video Container

A set of organized possible parameters including compression or codec, color depth, audio type/compression selected for the intended use, and even subtitles.

Video Format

Consists basically of a set of rules and parameters that define industry wide video. This is the native resolution, color depth, the frames per second among other parameters. Video format examples are the DVD video format, the 3GP video format or1080p and 1080i formats.

Sound

The brain's perception of the vibration of a medium that causes sound pressure waves.

Loudness/ Volume

Measured in decibels (symbol: dB). In sound, that would be how much more or less pressure there is from the base pressure. The threshold of hearing is the point where an average person can begin to hear a sound.

Dynamic Range

The difference or the range between the loudest sounds and the quietest sounds. Dynamic range can be exciting when you are listening to music but is often a problem for performance works like dance. You may have to decrease the dynamic range so that the audience can hear the quietest parts, while not being assaulted by the loudest parts

Cycle

A cycle is the wave from start, or a repeatable point, through 360°, back to that repeatable point.

Frequency

Determines pitch. It is determined by the number of cycle per second. It is measured in hertz, symbol Hz.

Humans have a range of hearing from roughly 20 Hz to 20,000 Hz (20KHz). This range of hearing decreases with age, abuse, and fatigue.

Velocity Sound requires a medium to travel through. The speed of sound is generally determined by the density and elasticity of the medium. So generally speaking, sound travels faster through water than air etc.

As a rough number, the speed of sound is 1130 feet per second in air at 70 degree Fahrenheit, at sea level. In comparison, light travels at 186,000 miles per second.

Velocity

Sound requires a medium to travel through. The speed of sound is generally determined by the density and elasticity of the medium. So generally speaking, sound travels faster through water than air etc.

Timbre

What differentiates one sound source from another. Also referred to as tone, or the color of the sound. It is determined by the relationship between the fundamental and the harmonics. Different instruments playing the same note will sound different because they do not produce the same ratio of sound between the fundamental and the partials, or harmonics.

Envelope

Instruments also sound different because of the sound envelope they produce. He sound envelope is made up of four parts: attack, decay, sustain, and release. The attack is the time taken for the amplitude to build to its peak. The decay is the initial decay after the attack. The sustain is the changes in the note as it is held out, and the release is how the sound finishes after being played.

Masking

The psychoacoustic phenomenon where loud sounds will prevent the ear from hearing.

Perception of Direction

Can only occur because we have at least two ears separated by an acoustical block (your head). Lower frequencies seem less directional. Higher frequencies are more directional and are more easily reflected. We can tell the direction of the sound in the horizontal plane with greater accuracy than in the vertical plane.

Acoustics

The reflective and absorptive qualities of a space.

Reverberation

The persistence of a sound after the original sound has stopped. When a sound reverberates, the multiple sounds are not distinct. When that sound is distinct, that is an echo. Reverberation is often nice for music. Reverberation negatively affects our understanding of the spoken word, because we rely on the clarity of the sound to understand the words

Reinforcement

The amplifying of live sound for the purposes of making it louder.

Analog

Signals are direct interpretations of the original signal. This could be in a magnetic, electrical, or physical form.

Digital

Recordings sample the sound every so often, and that sample is converted to a binary number or code, 1's & 0's, to represent that sample.

The reason we have moved to digital processing is that analog equipment can add noise to the process, and change the signal. Digital equipment just trades code. That original sampled signal will never be changed. You can make as many copies as you want.

Think of bit depth as how detailed you can be about each sample. The greater the bit depth, the higher the quality.

Transducer

A device that converts one type of energy to another.

Signal Path

The path of an audio signal from start to finish.

Microphone level

The extremely weak signal produced by a microphone. It is susceptible to radio and electrical interference.

Line Level

A somewhat standardized type of signal, stronger than microphone level, used between the mixer to the amplifier

Mono

Signal is one track or path

Stereo

Signal has two distinct tracks or paths; one left, one right.

Surround Sound

Uses multiple tracks or paths to provide sound imaging in multiple dimensions.

Microphone

Converts a sound pressure wave into a very weak electrical signal.

Pickup Pattern

he pattern of acceptance or rejection of a microphone; where it accepts sound from.

Condenser Microphones

Condenser microphones need a power source, dynamic microphones do not. This power is either provided by a battery in the microphone, or phantom power is provided from the mixer or other piece of equipment that the microphone is attached to.

Boundary Microphones

Microphones meant to sit on the floor, table or on a wall.

Boom Microphones

Are mics, usually hyper cardioid mics, attached to a long pole or boom that is operated by a boom operator, pointing the mic at the sound source.

Wireless Mic Systems

Basically small radio stations, consisting of a microphone (with or without a small cable), a transmitter and a receiver.

Our main issue with these is where to put the transmitter so that it will not be damaged. It usually winds up in the small of the back. The next issue is where to put the microphone. This could be on a boom placed around the ear, sticking just out of the hairline (on elastic- called a halo), etc.

Care of a wireless microphone and transmitter worn on the body

The transmitter and antenna need to be protected from sweat. One of the easiest ways to do this is to place the transmitter in a non lubricated condom before attaching it to what ever will attach it to your body, (a shirt with a pocket, wide elastic, etc.).

Wireless mics use batteries. Start each show with a fresh, non-rechargeable battery.

Digital Audio Files and Computer Control

Computers, and electronic devices can record/store, access and playback digital audio files. Always buy the higher quality AIFF or WAV files for production purposes. MP3's and many other compressed forms are not of a high enough quality

Digital Signal Processor

Converts digital signals from your computer to analog signals to be used by the mixer or other equipment, or vise versa, converting analog signals to digital so they can be processed or recorded by your computer.

Mixer

The purpose of a mixer is to simply mix various inputs and send them to various outputs. Typical inputs for a show might include:

- Audio sends from Qlab or other sound source playing back prerecorded audio for the show. This would be at least two sends, a left and right, but could be many more.

- Boundary microphones across the front of the stage.

- Wireless mics worn by performers.

- Microphone for announcements to the house.

- One or many sends from live musicians, miced for reinforcement.

- A mic for picking up audience reaction, Etc.