The power of Sound
MIDI Vs Digital audio
Multimedia system sounds
Audio File Formats
Vaughan’s Law of Multimedia Minimums
Adding sound to Multimedia project
Vibrations in the air creates waves of pressure that are perceived as
Sound waves vary in sound pressure level (amplitude) and in
frequency or pitch.
‘Acoustics’ is the branch of physics that studies sound.
Sound pressure levels (loudness or volume) are measured in decibels
Humans hear sound over a very broad range
Sound is energy, caused by vibrations of the molecules.
Too much volume can permanently damage your ears and
The perception of loudness depend on the frequency or pitch.
Harmonics cause the same note played on a cello to sound
different from one played on a piano.
Digital audio is created when you represent the characteristics of
sound wave using numbers - a process referred to as Digitizing.
We can digitize any sound.( Microphone, synthesizer….).
Digitized sound is sampled sound.
Every nth fraction of a second , a sample of a sound is taken and
stored as digital information in bits and bytes.
The quality of digital recording depends on the how often the
samples are taken.
i.e higher the sampling rate better is the quality of sound.
Sampling rate is measured in KiloHertz.
Three sampling rates are normally used in Multimedia 44.1k Hz
(CD- Quality) , 22.05 kHz and 11.025 kHz.
Larger the sample size , more accurate data will describe the
The value of each sample is rounded off to the nearest integer, called
It’s a straight forward process.
Plug a microphone in its jack , Then make use of audio digitizing
software like Audacity to do the work.
2 crucial aspects to be considered :
1) Balancing the need for sound quality against the file size.(Higher
Quality Larger File size).
2) Setting proper recording levels to get a good ,clean recording.
What type of recording to be considered?
We need to use a good piece of Digital audio recording and editing
software that displays digital meters.
Once the recording has been made, It will almost be necessary to edit
it using the required tools available in the software.
Basic sound Editing operations :
2. Splicing and assembly
3. Volume and adjustments
4. Format conversion
5. Resampling and
6. Fade in and Fade out
8. Time Stretching
9. Digital Signal
10. Reversing sounds
11. Multiple Tracks
1. Trimming : Removing dead air or blank space and so on. Done
using commands like cut , clear , Erase, Silence.
2. Splicing and Assembly : Removal of extraneous noise , touch
up, creating a longer recording by mixing many small recordings.
3. Volume adjustments : when we combine one or more recording
with different volume level, they must be made to run with a
consistent vol. level. We need to normalize it with a sound editor
to a particular level.
4. Format Conversion : While saving different formats are made
available for sounds. Data may be lost during conversion.
5. Resampling and downsampling : if we have sound recorded and
edited the sound at 16 bit sampling rate and using lower rates then
RS & DS is necessary, as we may save lots of disk space.
6. Fade in & Fade out :useful for sections that requires this effect.
This enveloping helps to smooth out a beginning and end of the
7. Equalization : allow us to modify a recordings frequency content
so that it sounds brighter or darker .
8. Time Stretching : allows to alter the length of the file . Useful but
may degrade audio quality of the file.
9. Digital Sound Processing : allows signals with reverberation, multi
tap delay, chorus, flange and other special effects using DSP
10. Reversing Sound : Reversing or a part of a recording.
11. Multiple Tracks : Being able to edit and combine multiple tracks,
merge tracks and then export them in a final mix to a single audio
file is important.
Musical Instrument Digital Interface :
is a communications standard developed in the 1980’s for electronic
instruments and computers.
It allows instruments from different manufacturers to
But MIDI data is not digitized, its only music data stored in
Digital Audio is recording where as MIDI is a score.
A MIDI file is a list of time stamped commands that are recordings
of musical actions.
Using MIDI, we can easily and quickly compose our own original
The process of creating MIDI is quite different from digitizing a
Digitized Audio Bitmap Image then MIDI Vector graphics.
For digitized audio we simple need to play the recording through a
computer device that can digitally record the sound.
To make MIDI, we need :
MIDI software creates data about each note as it has been played on a
MIDI keyboard which note, how much pressure was put on each
key, how much time the sound sustained……….
This information, when played back through MIDI device , allows
the same to be reproduced exactly.
MIDI files are more compact than audio files.
MIDI is small , can be easily embedded into the web pages.
If the MIDI sound source is of high quality, this sounds better than
MIDI data is completely editable.
MIDI data can be easily converted to musical notations and vise
MIDI does not represent sound, there fore cannot be used for
MIDI cannot be easily used to playback a spoken dialog, although
expensive and technically tricky digital samplers are available.
A. Digital audio wont work when there isn’t enough memory or
B. When there is high quality MIDI sound source.
C. When we have complete control over the machine on which the
program is going to be delivered.
D. We don’t need spoken dialog.
It has a consistent playback quality.
A wider selection of application software and system support for DA
is available in Win and Mac platforms.
Preparation and programming of DA doesn’t require the knowledge
of music theory.
We don’t need control over the playback Hardware.
When we have enough bandwidth and computing resources.
When spoken dialog is required.
We can use sound on computer for any action performed with it.
Open the sound control panel to listen to the system sounds ,
change them, make new , or custom sound.
In windows, sounds are wave files, they reside in Windows/Media
They include chimes.wav, chord.wav , logoff.wav and so on.
In OS X on Mac system, we can only change the system alert sound.
Custom sound should be added into System/Library/Sounds
subdirectory in AIF Format.
A sound file’s format is a recognized methodology for
compressing data bits of digitized sound into a data file.
The structure of the file must be known even before the data
can be saved or later loaded into a computer to be edited or
played as sound.
The file name extension identifies the method of storage used.
On the Macintosh, digitized sounds may be stored as data files,
resources, or applications such as AIFF or AIFC.
In Windows, digitized sounds are usually stored as WAV files.
Both can use MIDI files (.mid).
The method used for consumer grade music CD’s is Linear Pulse
Code Modulation (LPCM shortened to PCM)
CD-ROM/XA (Extended Architecture) format for reading and
writing CD’s was developed later so one can put several recording
sessions of music to be placed on a single CD-R .
LPCM tracks from an Audio CD are usually converted and stored on a
computer in uncompressed AIFF or WAV format.
AIFF Audio Interchange File Format
WAV Wave Format
There are huge number of file formats and “Multimedia Containers”
that store sound data
There are converters to read and write sound files from one format
MP3 was developed by MPEG (Moving Picture Expert Group).
•Common method for storing consumer audio.
•Contains lossy compression algorithm to save space.
•Evolved in early 1990’s.
Example : An audio CD may hold an hours uncompressed LPCM, if
the same content is stored in MP3 format then we can store 7 hours
content with a slight loss in quality.
WMA (Windows Media Audio) is a proprietary format developed to
OGG was developed as an open – source and royalty free “Container”
for sound compressed using the “Vorbis algorithm”.
Vorbis sound data resides within an OGG container OGG Vorbis
MP4 format is based on Apple’s Quick Time Movies(.mov)
It is similar to the MOV format that stores different types of media.
MP4 extension is used when file streams audio & video together.
M4a extension is used only when file contains only audio data.
M4p extension contains only audio, but encrypted for Digital Rights
M4r files are used for ringtones on Apple’s iPhone.
Other GSM phones use 3gp file format for ring tones.
Advanced Audio Coding (AAC) format is adopted by Apple’s iTunes
Default format for iPod , iPhone , PlayStation ,Wii, Dsi , Motorola ,
Nokia , Philips , Samsung , Siemens and Sony Ericsson.
Codec is a software that compresses a stream of audio or video for
data storage or transmission and then decompresses it for play back.
Some are “lossy” trade quality for reduced file size transmission
Some are “lossless” original data is not at all altered.
Liebig’s Law of Minimum :
The evolution of eyesight , loco motor speed , sense of smell , or any
other species trait will cease when that trait becomes sufficiently
adequate to meet the survival , requirements of the competitive
If the trait is good enough , the organism expends no more effort
There is an acceptable minimum level of adequacy that will satisfy
the audience, even when that level not be the best that technology ,
money , or time and effort can buy.
Following steps are required to bring an audio recording into MM
1. Determine the file formats that are compatible with MM
authoring S/W .
2. Determine the sound playback capabilities that the end user’s
3. Decide the type of sound needed.
4. Decide where and when you want to use the digital audio or
5. Acquire source material by creating it from scratch or buying it.
6. Edit the sounds to fit your project.
7. Test the sounds to be sure they are timed properly with the
project’s images. (This may involve steps 1-4 until everything is in
Large amount of digital information is required for high quality
Which in turn requires large amount of space.
If monaural sound is adequate then one can cut the storage space by
half or get double the playing time in the same memory space.
With compression codecs we can reduce the size to 1/8th the space
but there is loss of quality.
We can also downsample.
The following formula helps you to estimate your storage needs.If
you are using 2 channels for stereo then double the space.
(Sampling rate * bits per sample) / 8 = bytes / sec
The same can be solved in terms of KiloBytes :
Sample rate * sample size / 8 * # sec * 2 (if stereo) = file size in KB
If we require CD quality recording, then digitize sound at 44.1 kHz
and 16 bit to store, at a sound studio.
If we decide to do it our self then we need to invest in :
acoustically treated room ,
high end amplifiers ,
recording equipments ,
Digital Audio Tape (DAT) systems provide a tape based 44.1 kHz
and 16 bit record and playback capability.
DAT recordings are too accurate, precisely recording glitches,
background noises, microphone pops , including coughs in the next
A good editor can reduce the impact of these noises but at the cost
of time and money.
Mobile phones can record audio. USB , flash memory recorders can
be used to record and the recordings can be downloaded directly as
digital files using USB cables or card readers.
When a project has many sounds , its important to maintain a good
database , keeping a physical track of original material just in case
you need to revert it when the disk drive crashes.
The method for digitally encoding the high quality stereo of the
consumer CD market is an international standard , ISO 10149.
Also known as “Red Book Audio “ standard.
Converter & burning s/w’s such as Toast and CD creator from
Roxio can translate digital files of RBA found on CD directly to
digital sound file formats like MP3 & WAV.
Ringtones are normally associated with phones.
Telephone systems pulsating at 90 volt signal is sent to
copper wire to energize the hammer like klangs a bell.
But in the present systems, the mobile’s s/w takes the charge when
come one calls, depending on the programmed options, plays the
users choice of ring tone.
Ring tones play on very small speakers & often compete in a noisy
The other tones include answer tones , sing tones , true tones , real
tones , video tones & ringles.
There are many methods by which we can play sound on a web page.
Sound is actually not a part of web page as it has it is a separate file
with its own address & is embedded into the page.
The simplest way to embed a sound file is to se an inline HTML
<a href=“sound.wav”> Click here to listen to sound </a>
The text “Click here to listen to sound “ would be underlined, when
we click on it the browser will find the file mysound.wav, download
it, and opens a player to play the sound.
Media players are designed to play files as soon as enough of the data
is cached in computer’s buffer .
Downloading continues to fill the buffer faster, then you empty it by
playing the sound allowing the sound file to stream .
Streaming files are dependant on connection speed:
When using dial up modem, it is very slow.
While using DSL , its much faster.
When lots of things are involved in a project , problems don’t
emerge until we start testing.
Evaluate the sound storage medium.
Calculate the amount of RAM required and so on.
In the world of professional films & video production, sound is
incorporated during post production or post session , after all the
film and video footage has been assembled.