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Unit 3.1 Multimedia Basics

Using Sound

Sound enhances a multimedia application by supplementing presentations, images, animation, and video. In the past, only those who could afford expensive sound recording equipment and facilities could produce high-quality, digital sound. Today, computers and synthesizers make it possible for the average person to produce comparable sound and music. In multimedia applications, sounds are either content sounds or ambient sounds.

Content sounds furnish information. Narration and dialog are content sounds. Music and other sounds can also be considered content sounds if they are part of the topic itself. For example, the sound of a motor would be content sound if it were used to distinguish between different engine problems.

Ambient sounds include background sounds and special effects. Ambient sounds reinforce messages and set the mood. Music is a universal language that most people enjoy and appreciate. Classical music might be used in the background to set the mood for a multimedia application on literature and the arts while new age rhythms would be better for a multimedia application on the healing power of crystals. Special sound effects can reinforce or enliven a message. Different types of laughter could be incorporated into a multimedia application that included comic relief such as knock-knock jokes. As bullets enter the presentation screen in Microsoft PowerPoint, special sounds draw attention to and reinforce the bulleted item. Like every other multimedia element, if you decide to incorporate sound into a multimedia application, you should have a reason for doing so. In other words, you shouldn't use sound just because you can. Along the same lines, don't assume that more is better. Using too much sound is rarely a problem because most people fail to add it where it could truly enhance an application, but do keep in mind that balance is important.

Sound adds another dimension to a multimedia application, If used well, it is an extremely powerful element that can stimulate emotional responses that would never be activated from text and graphics alone. Sound should be used selectively and appropriately whenever and wherever it will help convey the intended message or complement the purpose of the multimedia application. Sound can be used to get attention, to entertain, to give directions, to personalize an interface, or to convey an educational or persuasive message. Audio on the Web can either be downloaded or streamed. Downloadable sound files are stored on your computer before they are played. Streaming is a more advanced process that allows the sound to be played as it is downloading.

Mono versus Stereo Sound

Mono sounds are flat and unrealistic compared to stereo sounds, which are much more dynamic and lifelike. However, stereo sound files require twice the storage capacity of mono sound files. Therefore, if storage and transfer are concerns, mono sound files may be the more appropriate choice.

Analog vs Digital

There are two types of sound: analog and digital. Analog sound is a continuous stream of sound waves. To be understood by the computer, these sound waves must be converted to numbers. The process of converting analog sounds into numbers is called digitizing or sound sampling. Analog sounds that have been converted to numbers are digital sounds. When we are working with digital sound, we call it audio. Therefore, sound that has been converted from analog to digital is often called digital audio sounds. Once a sound has been recorded, digitized, processed, and incorporated into a multimedia application, it is ready to be delivered. So that you can hear it through your speakers, the digital sound is sent through a digital-to-analog converter (DAC).

The delivery system will vary as the intended audience of the multimedia application changes. When considering the delivery of sound, you should consider the number of different sounds that will be delivered, how they will be delivered, where they will be delivered, and to whom they will be delivered. In other words, the application may include one voice and some background music designed for one user in front of a desktop computer or it may be a presentation with various different types of music, narration, and special effects designed for a larger audience to be presented in an auditorium. Regardless, a high quality delivery system will help ensure that the sounds you've worked hard to create make the right impression. There are many different types of digital audio file formats that have resulted from working with different computer platforms and software. Some of the better known formats include:

WAV is the Waveform format. It is the most commonly used and supported format on the Windows platform. Developed by Microsoft, the Wave format is a subset of RIFE RIFF is capable of sampling rates of 8 and 16 bits. With Wave, there are several different encoding methods to choose from including Wave or PCM format. Therefore, when developing sound for the Internet, it is important to make sure you use the encoding method that the player you're recommending supports.

AU is the Sun Audio format. It was developed by Sun Microsystems to be used on UNIX, NeXT & Sun Sparc workstations. It is a 16-bit compressed audio format that is fairly prevalent on the Web. This is probably because it plays on the widest number of platforms.

RA is Progressive Networks RealAudio format. It is very popular for streaming audio on the Internet because it offers good compression up to a factor of 18.

AIFF or AEF is Apple's Audio Interchange Format. This is the Macintosh waveform format. It is also supported on IBM compatibles and Silicon Graphics machines. The AIFF format supports a large number of sampling rates up to 32 bits.

MPEG and MPEG2 are the Motion Picture Experts Group formats. They are a compressed audio and video format. Some Web sites use these formats for their audio because their compression capabilities offer up to a factor of at least 14: 1. MIDI (MID, MDI, MFF) is an internationally accepted file format used to store Musical Instrument Digital Interface (MIDI) data. It is a format used to represent electronic music produced by a MIDI device (such as a synthesizer or electronic keyboard). This format provides instructions on how to replay music, but it does not actually record the waveform. For this reason, MIDI files are small and efficient, which is why they are often found used on the Web. On a PC, MIDI files will have a mid extension.

SND is the Sound file format developed by Apple. It is limited to a sampling rate of 8 bits, and is used primarily within the operating system.

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