MULTIMEDIA SOUND & AUDIO

Sound-Audio-Introduction:

        Sound is perhaps the most important element of multimedia. It is meaningful “speech” in any language, from a whisper to a scream.

        It can provide the listening pleasure of music, the startling accent of special effects or the ambience of a mood setting background.

        Sound is the terminology used in the analog form, and the digitized form of sound is called as audio.

    Power of Sound:

        When something vibrates in the air is moving back and forth it creates wave of pressure. These waves spread like ripples from pebble tossed into a still pool and when it reaches the eardrums, the change of pressure or vibration is experienced as sound.

        Acoustics is the branch of physics that studies sound. Sound pressure levels are measured in decibels (db);

        A decibel measurement is actually the ratio between a chosen reference point on a logarithmic scale and the level that is actually experienced.

    Multimedia Sound Systems:

        The multimedia application user can use sound right off the bat on both the Macintosh and on a multimedia PC running Windows because beeps and warning sounds are available as soon as the operating system is installed.

        On the Macintosh you can choose one of the several sounds for the system alert.

        In Windows system sounds are WAV files and they reside in the windows\Media subdirectory.

        There are still more choices of audio if Microsoft Office is installed.

        Windows makes use of WAV files as the default file format for audio and Macintosh systems use SND as default file format for audio.

    Digital Audio:

        Digital audio is created when a sound wave is converted into numbers – a process referred to as digitizing.

        It is possible to digitize sound from a microphone, a synthesizer, existing tape recordings, live radio and television broadcasts, and popular CDs.

        You can digitize sounds from a natural source or pre recorded.

        Digitized sound is sampled sound. Ever nth fraction of a second, 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 (sampling rate or frequency, measured in kilohertz, or thousands of samples per second)

        The three sampling rates most often used in multimedia are 44.1 kHz (CD-quality), 22.05 kHz, and 11.025 kHz.

        Sample sizes are either 8 bits or 16 bits.

        An 8-bit sample size provides 256 equal measurement units to describe the level and frequency of the sound in that slice of time.

        Quantization: The value of each sample is rounded off to the nearest integer.

        Clipping: If the amplitude is greater than the intervals available, clipping of the top and bottom of the wave occurs.

        Quantization can produce an unwanted background hissing noise, and clipping may severely distort the sound.

 

    Preparing Digital Audio Files:

        Preparing digital audio files is fairly straight forward. If you have analog source materials – music or sound effects that you have recorded on analog media such as cassette tapes.

·         The first step is to digitize the analog material and recording it onto a computer readable digital media.

·          It is necessary to focus on two crucial aspects of preparing digital audio files:

o   Balancing the need for sound quality against your available RAM and Hard disk resources.

o   Setting proper recording levels to get a good, clean recording.

        Remember that: the sampling rate determines the frequency at which samples will be drawn for the recording. Sampling at higher rates more accurately captures the high frequency content of your sound. Audio resolution determines the accuracy with which a sound can be digitized.

         

    Formula for determining the size of the digital audio:

Monophonic: Sampling rate * duration of recording in seconds * (bit resolution / 8) * 1

Stereo : Sampling rate * duration of recording in seconds * (bit resolution / 8) * 2

        The sampling rate is how often the samples are taken.

        The sample size is the amount of information stored. This is called as bit resolution.

        The number of channels is 2 for stereo and 1 for monophonic.

        The time span of the recording is measured in seconds.

         

    Editing Digital Recordings:

        Once a recording has been made, it will almost certainly need to be edited. The basic sound editing operations that most multimedia procedures needed are described in the paragraphs that follow

        Multiple Tasks: Able to edit and combine multiple tracks and then merge the tracks and export them in a final mix to a single audio file.

        Trimming: Removing dead air or blank space from the front of a recording and an unnecessary extra time off the end is your first sound editing task.

        Splicing and Assembly: Using the same tools mentioned for trimming, you will probably want to remove the extraneous noises that inevitably creep into recording.

        Volume Adjustments: If you are trying to assemble ten different recordings into a single track there is a little chance that all the segments have the same volume.

        Format Conversion: In some cases your digital audio editing software might read a format different from that read by your presentation or authoring program.

        Resampling or down sampling: If you have recorded and edited your sounds at 16 bit sampling rates but are using lower rates you must resample or down sample the file.

        Equalization: Some programs offer digital equalization capabilities that allow you to modify a recording frequency content so that it sounds brighter or darker.

        Digital Signal Processing: Some programs allow you to process the signal with reverberation, multi tap delay, and other special effects using DSP routines.

        Reversing Sounds: Another simple manipulation is to reverse all or a portion of a digital audio recording. Sounds can produce a surreal, other wordly effect when played backward.

        Time Stretching: Advanced programs let you alter the length of a sound file without changing its pitch. This feature can be very useful but watch out: most time stretching algorithms will severely degrade the audio quality.