Transcript Document

Sound
 Importance of sound
 How to make sound (types)
 How to record and edit sound on your
computer
 How to incorporate sound in your MM work
Intro to Sound
We rely on SOUND to enhance Multimedia
Applications
WHY?
Easily capture the attention of users
Facilitate easy learning
Set the mood
On the Web, sound offers
 Background music, narration, and sound effects
Create moods
 Recorded testimonials from customers are used to market and
sell products and services.
 Interviews with stars and listening to a sample of their
achievements
 One-way audio offers on-demand radio listening around the
world. These radio programs broadcast music, talk shows, and live
interviews.
 Internet Audio Conferencing or Internet telephony that allows
two-way, full-duplex audio conversations over the Web. With
Internet telephony you can talk to friends or family without the cost
of a long-distance phone call.
What is Sound?
Sounds are pressure waves of air
Visualize the sounds as a series of
recurring waves called a waveform.
Volume - the higher the wave the higher
the sound
Pitch or frequency number of cycles
per second (cps), or Hertz
Bells
Oh
Sources of Sound
Pre-packaged
•
Some sound files may come with your computer's operating system or with
programs that are installed on your computer.
Purchased or Borrowed
•
Download from stock companies – $$$ or provided free
Create Your Own Sound Clips
•
Recording program with a computer's operating system (such as Sound
Recorder) and speak into a microphone attached to the computer – quality will
not be the best
•
Recording studio with equipment such as DAT (Digital Audio Tape) devices that
record sounds digitally. Produces a high quality commercial product
•
Electronic instruments such as synthesizers can be used to create music
sound files. Connecting the instrument to a computer allows the sounds to be
captured in a MIDI (Musical Instrument Digital Interface) format.
How is Sound Recorded?
(electrical signal)
analog
•Microphone translates
movement into electrical
signals (analog). Then
tape recorder translates
the waveform from an
electrical signal on a wire,
to a magnetic signal on a
tape (analog)
•Analog-to-Digital
Converter (ADC). The
ADC captures a
snapshot of the
electric voltage on an
audio line and
represents it as a
digital number that can
be sent to a computer.
Digital audio
 It is the actual representation of
sound stored in the form of digital
numbers (Samples)
 It represents the loudness of the
sound at a slice of time
 It sounds the same every time
played.
How is Sound Recorded and Played?
What is Digital Format?
In a multimedia application sound must be in a
digital form (string of 1s and 0s).
 A sound can be recorded directly in digital form or an
analog sound can be converted to a digital sound.
To convert analog sounds to digital sounds a
technique is used called digital sampling
Digital audio sampling I
 Sampling: is converting the
sound wave to numbers
using the magnitude of the
wave. That is from analog to
digital. How?
 Divide the horizontal axis
(the time dimension) into
discrete uniform pieces.
 Sample rate (frequency): is
how often the samples are
taken (fraction of a second)
Digital audio sampling II
 Sample size: the amount of information
stored about each sample 8 or 16 bits .
Also known as bit depth.
 Quantization – divide the vertical axis
(signal strength) into pieces.
Sometimes, a non-linear function is
applied.
 – 8 bit quantization divides the
vertical axis into 256 levels. 16 bit
gives you 65536 levels.
Nyquist’s Sampling Theorem

How many Samples to take?
11.025 KHz — Speech
(Telephone 8KHz)
22.05 KHz — Low Grade Audio
(WWW Audio, AM Radio)
44.1 KHz — CD Quality
For lossless digitization, the
sampling rate should be at
least twice the maximum
frequency responses.
 Indeed many times more
the better.
Memory Required for 1 Minute
of Digital Audio
Reasons to use digital audio
 It is consistent: the digital media will sound as
good at the end as it did in the beginning when
it was created.
 A wider selection of application software and
system support for digital audio is available.
 The preparation and programming required for
creating digital audio do not demand
knowledge of music theory;
 working with MIDI data usually does require
familiarity with musical scores, keyboards, and
notation as well as audio production.
Preparing digital audio files
 Two important aspects have to be taken in
considerations while preparing sounds:
1. Balancing the sound quality with the available
hardware resources.
Remember the relation between sampling frequency
and sound quality?
2. Setting proper recording levels to get clean
recording. If Recording level too high, it will
introduce noise. Conversely if it is too low it is
useless.
QUALITY OF DIGITAL RECORDING
 Depends ON
1. Sample Rate
2. Sample Size (level)
3. Channels
4. Codecs
QUALITY OF DIGITAL RECORDING
Channels
 Mono signal
one stream of data reproduced equally on both speaker
channels
Lose stereo separation
 Stereo signal
consists of two streams of data working together
(left,right)
double the size of mono file
QUALITY OF DIGITAL RECORDING
Quality
QUALITY OF DIGITAL RECORDING
CODECS
 Software programs that greatly
compress the audio file size
 Codecs use lossy compression by
removing redundant and less-significant
data
How big can audio get?
 An example of uncompressed sound with CD
quality for 1 minute of audio:
 1 minute of recording  60 seconds
 60 * 44,100 samples/second  2,646,000
samples
 2,646,000 samples * 16bits per sample 
42,336,000 bits
 42,336,000 bits * 2 (stereo, 2 channels) 
84,672,000 bits
 84,672,000 bits / (8bits per byte)  10,884,100
 About 10 MB (Megabytes)!!!
Musical Instrument Digital Interface
MIDI sounds
 Allows sounds synthesizers from different
manufacturers to communicate with each other by
sending messages along cables connected to
devices.
 MIDI is a standard for encoding music, not sound. That
is a shorthand representation of music stored in
numeric form
 Contains instructions for creating the frequency, volume and
duration of notes that sound like various musical instruments
 MIDI files are recording of musical actions for
example:
 Pressing a piano key.
Midi versus digital audio


MIDI files are much more compact than digital audio files.
The size of a MIDI file is completely independent of
playback quality.
In general, MIDI files will be 200 to 1,000 times smaller
than CD-quality digital audio files. For example:
 MIDI
 21KB, 2min 36s
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Digital Audio
 612KB, 56s
Because MIDI files are small, they don’t take up as much
RAM, disk space, and CPU resources.
Which one is a live recording and which one is computer
generated? Can you tell the difference?
 One
 Two
Where to use Midi
 Because they are small, MIDI files
embedded in Web pages. When loaded,
MIDI files play more quickly than their
digital equivalents.
 Midi files are editable, thus it can be used
in the application where it might be needed
to change the length of the file without
changing the quality of the audio quality.
 Digital audio wont work because you don’t
have enough RAM, hard disk space, CPU
processing power, or bandwidth.
 don’t need spoken dialog.
Disadvantages of using MIDI files
 You can’t be certain that playback will be
accurate if the MIDI playback device is not
identical to the device used for production.
 Does not produce high-quality vocals ‫غناء‬
 Even with the General MIDI standard the
sound of a MIDI instruments varies according
to the electronics of the playback device and
the sound generation method it uses.
 Also, MIDI cannot easily be used to play back
spoken dialog.
Components of a MIDI System

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Synthesizer:
 It is a sound generator (various pitch, loudness, tone
colour).
 A good (musician’s) synthesizer often has a
microprocessor, keyboard, control panels, memory, etc.
Sequencer:
 It can be a stand-alone unit or a software program for a
personal computer. (It used to be a storage server for
MIDI data. Nowadays it is more a software music editor
on the computer.
 It has one or more MIDI INs and MIDI OUTs.
Track:
 Track in sequencer is used to organize the recordings.
 Tracks can be turned on or off on recording or playing
back.
Components of a MIDI System


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Channel:
 MIDI channels are used to separate information in a MIDI
system.
 There are 16 MIDI channels in one cable.
 Channel numbers are coded into each MIDI message.
Timbre:
 The quality of the sound, e.g., flute sound, cello sound, etc.
 Multitimbral – capable of playing many different sounds at the
same time (e.g., piano, brass, drums, etc.)
Pitch:
 musical note that the instrument plays
Voice:
 Voice is the portion of the synthesizer that produces sound.
 Synthesizers can have many (12, 20, 24, 36, etc.) voices.
 Each voice works independently and simultaneously to produce
sounds of different timbre and pitch.
Patch: the control settings that define a particular timbre.
Making MIDI audio
 To make MIDI audio you need:
 Sequencing software
 Sound synthesizer
 A MIDI keyboard
 Instruments that can be synthesized are
identified by general MIDI numbering
system that ranges from 0 to 127
 Good sequencing software allow printing
and scanning the music sheets.
Adding sound to MM project

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Steps to bring audio recording into MM
project
Decide what kind of sound is needed (such as
background music, special sound effects, and
spoken dialog).
Decide where these audio events will occur in
the flow of your project.
Fit the sound cues into your story board, or
make up a cue sheet.
Decide where and when you want to use
either digital audio or MIDI data.
Other steps
 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. This may involve repeating
previous steps until everything in
sync.
Editing digital recording
 Once recording and digitizing been
made, editing will be made. Following
are list of editing operations that are
most used:
 Trimming: removing blank space from
the beginning and extra time at the end.
 Splicing and assembly: putting short
segments to gather in a longer one.
Other editing operations
 Volume adjustment: when assembling
different segments in one, the volume
may be not the same, thus it is
important to be able to adjust the sound
volume.
 Format conversion: one should be able
to convert audio files from one type of
files to types that director plays. It plays
AIFF, SWA, AU, or WAV audio files.
Other editing operations
 Resambling or downsampling: If you
have recorded your sound at 16-bit
sample size but are using lower rates
in your project, then you must edit
the file downsasmpling its contents.
 Fade-ins and fade-outs: beginning
and ending the sound gradually and
in a smooth way.
More editing operations
 Equalization: allow modifying recorded
content to sound brighter or darker.
 Time stretching: some programs allow
alter the length of the sound file
without changing the pitch(‫)النغمة‬
 Digital signal processing: add special
sound effects
 Reversing sound
Sound-Editing Software - cont
Audacity Software
Edit the clip,
Combine it with other
sound files Add
transitions or special
effects
Sound-Editing Software
- cont
Recording sound using
WaveStudio
Edit the clip,
Combine it with other sound files Add
transitions or special effects
Adding sounds
Uses for adding sounds
 We can mix sounds
 We even know how to change the
volumes of the two sounds, even over
time (e.g., fading in or fading out)
 We can create echoes
 We can add sine (or other) waves
together to create kinds of
instruments/sounds that never
existed in nature, but sound complex
Sound File Formats
Sound File Formats
- continued
So which format is best?
uncompressed
Computing the size of a digital
recording
 Sampling rate * duration (seconds) * (bit
resolution / 8) * 1 (mono) or 2 (stereo)
 E.g., for a 10 second recording at 20.05 kHz, 8bit resolution, monophonic (good for speech):
 22050 kilohertz * 10 seconds * 8/8 * 1 = 220,500
bytes
 Or, for 10 seconds of good music quality at 44.1
kHz, 16-bit resolution, stereo:
 44100 kHz * 10 * 16/8 * 2 = 1,764,000 bytes
 “Red Book” standard (ISO 10149) for CD-quality
audio
 Expensive for multimedia
 Playing 16-bit resolution requires 16-bit sound
cards