The Power of Sound

• When something vibrates in the air by moving back and forth, it creates waves of pressure and when they reach your eardrums, you experience the changes of pressure, or vibrations, as sound.


• Acoustic is the branch of physics that studies sound. Sound pressure levels are measured in decibels (dB).


• In order to make you multimedia become interesting you need to know the following:
  1. How to make sounds
  2. How to record and edit sounds on your computer
  3. How to incorporate sounds into your multimedia work

Digital Audio

• Digital audio is created when you represent a sound wave using numbers which called digitizing.


• You can digitize sound from a microphone, synthesizer, existing tape recordings, live radio and television broadcasts, and popular CDs.


• Digitized sound is sampled of sound; a sample of sound is taken and stored as digital information in bits and bytes.


• The quality of this digital recording depends upon how often the samples are taken and how many numbers are used to represent the value of each sample.


• The three sampling frequencies often used in multimedia are CD-quality 44.1 kHz (kilohertz), 22.05 kHz, and 11.025 kHz. Sample sizes are either 8 bits or 16 bits. The larger the sample size, the better the data recorded sound will be.

Editing Digital Recordings

The basic sound editing operations that most multimedia producers need are:

• Multiple Tracks


• Trimming


• Splicing and Assembly


• Volume Adjustments


• Format Conversion


• Resampling or Downsampling


• Fade-ins and Fade-outs


• Equalization


• Time Stretching


• Digital Signal Processing (DSP)


• Reversing Sounds

Making MIDI Audio

• MIDI (Musical Instrument Digital Interface) can let you compose your own original score.


• Creating an original MIDI score is hard work because it takes time and musical skill to work with MIDI.


• To make MIDI scores, you will need sequencer software and a sound synthesizer. The sequencer software lets you record and edits MIDI data.


• When it is in MIDI data there is a value that designates the instrument to be used for playing back the music. To change instruments, you just change the value.


• Instruments that you can synthesize by General MIDI numbering system that ranges from 0 to 127.


• Once you have gathered your audio material, you will need to edit it to precisely fit your multimedia projects.

Audio File Formats

• A sound file’s format is a recognized methodology for organizing the digitized sound’s data bits and bytes into a data file.


• On the Macintosh, digitized sounds stored as SNDs. In Windows, digitized sounds stored as WAV files.


• The CD-ROM/XA format for reading and writing CDs was developed to put several recording sessions onto a single CD-R (recordable) disc.


• The AIFF sound format is preferred for Macintosh sound files. The wave format (WAV) was introduced by Microsoft and IBM with the introduction of Windows.


• Both Macintosh and Windows can make use of MIDI files. On both platforms, MIDI sounds are typically stored in files with the .mid extension.

MIDI versus Digital Audio

• The advantages:
  1. MIDI files are much more compact than digital audio files
  2. MIDI files surrounded in web pages load and play more quickly than their digital equivalents.
  3. If the MIDI sound source you are using is of high quality, MIDI files may sound better than digital audio files.
  4. You can change the length of a MIDI file without changing the pitch of the music or degrading the audio quality. MIDI data is completely editable.


• The disadvantages:
  1. Only certain playback will be accurate if the MIDI playback device is identical to the device used for production.
  2. Midi data cannot easily used for play back spoken dialog.

Choosing Between MIDI and Digital Audio

• Use MIDI data in the following circumstances:
  1. Digital audio won’t work because you don’t have enough RAM, hard disk space, CPU processing power or bandwidth.
  2. You have a high-quality MIDI sound source.
  3. You have complete control over the machines on which program will be delivered.
  4. You don’t need spoken dialog.


• In general, use digital audio in the following circumstances:
  1. You don’t have control over the playback hardware.
  2. You have the computing resources and bandwidth to handle digital files.
  3. You need spoken dialog.

Adding Sound to Your Multimedia Project

• Determine the file formats that are compatible with your multimedia authoring software and the delivery medium you will be using.


• Determine the sound playback capabilities that the end user’s system offers.


• Decide what kind of sound is needed. Decide where these audio events will occur in the flow of your project.


• Decide where and when you want to use either digital audio or MIDI data.


• Acquire source material by creating it from scratch or purchasing it.


• Edit the sounds to fit your project.


• Test the sounds to be sure they are timed properly with the project’s images.

MUSIC CDs

• The method for digitally encoding the high-quality stereo of the consumer CD music market is international standard, called ISO 10149.


• This is also known as the Red Book standard.