Globe Theatrical Supply Resource Center 712/255-0972

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            INTRODUCTION to AUDIO <U>

GTS supplies a wide range of audio and associated equipment, designed primarily for performance and educational applications. Following is a brief introduction to considerations relating to the selection and application of audio equiment for training, performance, and general facility uses.

        THE BASICS

Sound is pressure waves. Moving through some material (walls, air, water, etc.), sounds are fundamentally described by frequency (audibly approximately 20 Hertz {Hz = cycles per second} bass to ~20,000 Hz treble) and intensity (volume = loudness).
Audio systems are generally intended to accomplish:
                sound transfer; for example, a paging system,
                volume increase; e.g., a stadium public address (PA) system,
 and/or     manipulation; e.g., recording studio mixing and editing.
Analog: The simplest system includes a microphone (input), an amplifier (volume control), and a speaker (output). The simplest microphone contains a small baffle (moved farther by increased pressure intensity and faster by increased pressure frequency) in a magnetic field, producing a direct duplicate (analog) low voltage, low amperage electrical signal. The amplifier electronically strengthens the very weak input signal and sends it to the speaker. The simplest speaker reverses the microphone process using a much larger baffle, restoring pressure waves to the available environment. If all components are of good quality, the audible output should be identical to the original sound source.
Few systems are this simple. Most include several inputs (mic's, tape, CD, etc.), a mixer to blend and manipulate the inputs to various outputs, several outputs (speakers, recorder, transmitter, etc.), and a variety of other monitoring and manipulation components (pre-amp, equalizer, effects, crossover, etc).
Digital systems "simplify" complex signal processing (manipulation) and output by allowing computer memory storage and recovery of equipment settings (similar to digital lighting consoles) and recording of consistent, low noise, low loss digital audio tapes (DAT) and compact discs (CD). However, to achieve a timely conversion of the extremely complex original analog source signal to a binary (computer format) signal only a portion (sample) of the original signal is used. The standard sampling rate is 44,100 Hz (2 or more samples per second, depending on analog frequency) and 24 bits of frequency/voltage readings.
The bottom line is that "live" quality is in the order of:
                Live (no audio system),
                Analog ("complete" waveform reproduction),
                Digital (sampled reproduction).
Unless specified as digital, all GTS listed audio equipment is analog.

GTS divides performance audio equipment into two major sub-categories - TRAINING AIDS and VENUE.
    TRAINING AIDS are divided as Variable-speed and Student Assistance. Fixed (surface and rack mounted) and portable (some battery powered) variable-speed equipment is most commonly used for movement arts (dance, gymnastics, skating, musicals) training and rehearsals; while Student Assistance equipment most frequently is installed in classroom "audio labs" or "media centers" for use with pre-recorded traditional school course materials.
    VENUE equipment includes performance facility (auditorium, church, outdoor, etc.), club, portable DJ, and intercom/public address/messaging systems.



Variable-speed playback is available as phonograph, cassette, CD, and DVD single or combined module units. Some models include amplifiers and speakers, capable of independent use; while others yield only line outputs requiring separate amplification and speakers. Some units also include key transposer circuitry, permitting music frequency correction when speed is adjusted - very useful for vocal or instrumental accompaniment. Wireless remote control may also be available. All listed cassette and CD-R units include audio recording capability. Portable units range from hand-held "pocket" size through higher amplification (volume capability) "karaoke" models to high output "rolling rack" public address units. Price and range of additional features vary significantly - REQUEST YOUR NEEDS.

            MEDIA LAB AUDIO

Student assistance systems include wired and wireless student headphone, audio-visual, and card reader systems. Some include compatible stereo, wireless instructor microphone/headset, and/or remote control units.

Also, a wide selection of  accessories and expansion components: playback units, microphones, jack-boxes, etc.; as well as, mixers, amplifiers, and speakers (discussion to follow).

        VENUE <U>

Installed facility audio usually requires several  interconnected components intended for little to no portability and capable of  high volume, larger area output. Minimally required are input components (microphones for live and/or playback units for pre-recorded), a mixer for separating and/or blending various inputs, an amplifier to increase the audio signal strength, and speakers to convert the signal to "sound pressure" (audio volume) through the air.

Additional common components include microphone stands, audio signal modification units, and intercoms (wired or wireless).

            MIXER <U>

The mixer is literally the heart of  an audio system. Here all input signals are manipulated and the outputs selected. Mixers are either analog  (allowing the passage of the complete input signal) or digital (pulsed binary, allowing easier signal manipulation and storage of multiple system settings for later use - similar to a digital light control console).

With few exceptions, mixers include separate input channels for each live microphone or musical instrument and playback (line) audio source, a potentiometer (pot) to adjust signal strength (volume) through each input channel, a mode switch per channel for selection if and to which output the channel signal is routed, a master potentiometer to adjust the mixed signal from the channel pots, output potentiometers for each output (monaural or stereo-pairs), a line output to the amplifier, and a monitoring (headphone or speaker) output for the user. Most mixers additionally include tone control per input channel permitting frequency adjustment, output channel VU (volume unit) meters indicating volume in decibels (db's), graphic equalizers (EQ) permitting adjusting signal strength (in db's) by frequency ranges per input and/or output channels, and a recording output.  All but the smallest mixers also include, at least, some of the following additional features: effects (mixer controlled) or effects output/input loops (using separate effects equipment) permitting echo and/or other audio effects, powered mic inputs (usually 48 volts, permitting use of cabled phantom powered condenser microphones), filters (high, mid, low, notch, bandpass, clip, peak, compression, etc.) allowing the the gain (increase) or attenuation (reduction) of narrow frequencies or signal qualities, program "memory" storage of all mixer settings for repeated reloading for reuse, networking ports (US224, RS232, midi, etc.) permitting external digital (computerized) control, and/or other circuirts.

                Analog Mixers

Most smaller (up to 24 input channels) mixers include no digital (binary) functions and are less expensive than digital units. They are ideal for  less complex applications, such as dance studios, skating rinks, small clubs or auditoriums. Analog mixers utlize the entire input signal, arguably permitting "full source" production. For this reason larger "professional" analog mixers are available for most applications from churches or theaters to recording studios.

                Digital Mixers

Digital mixers have three application advantages over analog models - console settings memory storage, very detailed/complex "instantaneous" signal manipulation, and digital recording output. Basic unit capacity is rated per recording tracks (channels), fidelity (commonly 24 bits) - the range of analog frequency voltages being converted to binary, and sampling rate (commonly 44.1 KHz) - .the number of binary samples taken per second versus the input signal frequency (generally  20 Hz to 20,000 Hz).



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A portion of this file was last updated 12/17/08.