Multimedia Plano ISD

Digital Audio: Intro, Terms and Resources

 

Introduction:

General Information

These steps and tips are intended to help with the process involved when you want prepare a sound clip, for use in a variety of applications. A quick, but very important, reminder before getting started is in order. It is your responsibility to follow any copyright laws and "fair use" guidelines that may pertain to what you are doing. If you are not sure, check with a Library Media Specialist on your campus. You may find it helpful to visit The Copyright Site to find out more about copyright and fair use guidelines.

  • There is no question that music can build mood - excitement, anticipation, danger, etc., communicate emotion - sadness, pride, joy, capture and hold the attention of your audience, reinforce interactivity with button sounds, make the audience feel like they're somewhere else, and give projects that "professional" feel. However, music, especially background music, need not always be "embedded" into a presentation to make it effective. Playing music from a portable CD player (jam box) can provide several advantages. You also have the option of having PowerPoint or other multimedia authoring application, just cue and play the CD track "live" during the presentation as well. (Make sure you test thoroughly using the hardware that will be used at the actual presentation though when planning to use this method.)

  • There are many factors that can help you determine which way to go. Some are: 1) file size and portability, 2) file size and load time, 3) overall length of presentation, number of clips, and how much sound (total length), 4) location, equipment, network access at the final presentation spot, 5) copyright and fair use issues 6) did I mention file size and hardware performance consistency.

  • As with any multimedia project, make sure you determine your target audience (the ultimate users that will experience or interact with your production), your "end result" performance environment (is this project being developed primarily for a "live" presentation, a cd-based experience, a Web-based delivery, VCR tape medium, etc., and what hardware and software will be available for the end user's (possibly yourself) when this project is delivered or experienced. This should include consideration of the quality of audio (sound) playback equipment as well. Once these elements are defined and planned, then begin the development (time investment) of your project. Knowing these elements in advance will likely help you make much wiser choices during development, save "re-do" time, and ultimately lead to a more successful end product!

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Digital Audio Terms:

AU (U-LAW) – Older audio compression file format, Sun Microsystems format that is popular in the Unix world. However, they have comparatively poor sound quality.

WAV (WAVE) – Standard Windows Format - A digitized sound file format for Microsoft Windows, which has ".wav" as the filename extension.

AIF (AIFF) – Standard (native) MAC Format for digital audio files.

MIDI (Musical Instrument Digital Interface) – A way of communicating instructions for playing music from one electronic device to another; for example, from a synthesizer to a computer to a musical instrument. MIDI includes hardware (the electronic instruments and the interface between devices) and software (the set of rules for encoding and transfer of sound information). With MIDI, a musician can use a keyboard to simulate the sounds of many different instruments, plus add special effects. MIDI files are very small compared to many other audio file formats and can be a very effective choice for digital use. However, the quality and range of tones used by this format is very limited. The resulting playback will use a set of standard synthesized instrumental sound tones. It will work well for some projects, it will depend on the reproduction quality you are after, as well as the access you have to the tools needed to prepare them and the playback ability of your target application. Because of it's small file size (fast download), midi has been an early "music" clip format favorite on the Internet.

MP3 – Popular Internet compression format - MP3 stands for "Motion Picture Experts Group, Audio Layer 3 Compression". A popular music download format, MP3 produces near-CD-quality music in a compressed file that can be transferred quickly, and played on any multimedia computer with MP3 player software. The technology creates sound files a tenth the size of standard CD music files with very little loss of sound quality.

WMA/AAC - Popular highly compressed format. These formats (WMA for Windows, AAC for Macs and iPods) are compressed to even smaller file sizes than MP3, but still retain a relatively high quality playback level. However, they generally require certain applications or devices for playback, thus, they are not completely reliable or compatible...yet, for inserting into PowerPoint or similar applications. Just make sure and test thoroughly before depending on them in your presentations and playback equipment.

RM (RealMedia) RAM, RA, etc. – Standard RealPlayer/RealAudio compressed format.

MPEG-1. An ISO (International Standards Organization) group that sets standards for compressing and storing video, audio, and animation in digital form. 2.The standards set by this group. MPEG is a lossy compression method. MPEG-1 is a standard for CD-ROM video and audio. MPEG-2 is a standard for full-screen, broadcast quality video. MPEG-4 is a standard for video telephony.

MOV (Movie)– Standard QuickTime format for movies and audio. Can also be audio only.

AVI (Audio Video Interleaved) – Standard Windows Video format. Can also be audio only. AVI is a Microsoft multimedia file format, similar to MPEG and QuickTime, used by Video for Windows. In AVI, audio and video elements are interleaved (stored in alternate segments) in the file.

Sample Rate - A sample rate (frequency) is the way a sound file is recorded. Sound Companion defaults at a Sample Rate of 22.05 KHz. What this means is that you will record @ 22.05 kilobytes per second. If you multiply this out, a one-minute file would be about 1.2 MB in file size. (Remember a regular floppy disk holds about 1.4 MB).

Bit Depth - Bit depth can be set at 8 or 16 bit. Sound Companion defaults to record at 16 bit. Bit depth describes the potential accuracy of a piece of hardware or software that processes audio data. Bit depth is the number of "bits" you have in which to describe something. Reminder a "bit" (short for binary digit), is the smallest unit of data in a computer. It has a single value, either "0" or "1". In most computer systems, there are eight bits in a "byte". For a more technical and thorough understanding and relevance to digital audio, visit Principles of Digial Audio

Here are some common general settings to use:

For "voice only" recordings: 11.025KHz - 16 bit
For "voice with background music": 22.05 KHz - 16 bit
For "sound clips recorded from a music CD": 22.05 KHz - 16 bit

These can get you started, but remember, you will usually want to go with those settings that strike an acceptable balance between file size and acceptable playback quality based on the target audience and target performance equipment that your project will be presented or played back with.

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Related Web Resources:

Note: some of these sites will not be accessible from a district machine. They are here as supplemental resources. You may be able to access them at home, if you choose to. Neither David Hitt nor PISD is responsible for the contents of remote sites or servers. If accessing any of these sites from a Plano ISD computer,you must follow and abide by all PISD Acceptable Use Guidelines for Technology Resources. (http://k-12.pisd.edu/aug.htm)

Make sure you follow legal and ethical use of all digital audio files. Read all documentation closely before using and/or editing sound clips from various sources. It is your responsibility to follow copyright and fair use guidelines. Your campus librarian can help with questions about this.

This is not an endorsement or recommendation to download or use any files and/or applications or plug-ins that may be available from these sites. It is intended as a resource to find out more about the various digital sound formats.

WAV and MP3:

http://electronics.howstuffworks.com/mp3.htm/printable - "How MP3 Files Work".

http://www.sandhills.cc.nc.us/software.html#av

http://accuweather.ap.org/cgi-bin/aplaunch.pl– Check the Associated Press/AccuWeather Multimedia Archive to search for sound files. (As this is a subscription-based service, remember that it can only be accessed when on the PISD District Network or via a Remote Access or MyPisd account login.)

http://www.altavista.com/cgi-bin/query?mmdo=13&stype=saudio

http://www.mtlc.net/ - Click on "Articles" for many tutorials, tips, and other "how-to's".

http://www.webreference.com/multimedia/audio.html

This page last modified June 20, 2007

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