Basic of Digital Audio

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Basic of Sound

2.1 Basic of Digital Audio

Sound: a travelling wave that

How sound waves interact

When two or more sound waves meet, they

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Speech Signal Frequency：300Hz-3kHz

Sound Frequency

Audio signals
Analog Signal: an electrical representation of sound originated by microphone,

Lifecycle of sound in Multimedia System

Procedure of audio digitalization

conversion to a stream of numbers, and preferably

Procedure of audio digitalization

Illustration

Sampling means dividing continuous time into discrete time

Understanding sample rate

Sample rate indicates the number of digital snapshots taken

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To reproduce a given frequency, the sample rate must be at

Understanding bit depth

When a sound wave is sampled, each sample is

dB(Decibel)

dB is commonly used in acoustics as a unit of

dBFS(dB relative to full scale)

dBFS(dB relative to full scale) is

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Data Size =Sample Rate×Bit Size×#Channel/8(Byte/s)

Affects of Data Size

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An audio file format is a file format for storing digital

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The bit layout of the audio data (excluding metadata) is called

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*.WAV Standard audio file container format used mainly in Windows PCs.

DRM Dataflow Diagram

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Audio Acquisition

i) Sound Recorder Software(eg. Sound Recorder in Win 7)
ii)

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2.5 Digital Audio Compression Standards

Introduction to Digital Audio Compression

Compression Encoding: the

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Lossless Compression
less space without losing any information.
compression ratio of about 2:1
Lossy

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Audio Compression Standards

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Comparison between common audio formats

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1993, MPEG-1 Audio Layer III
a digital audio coding format which uses

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2.6 Sound Card and Electroacoustic Equipment

Sound Card
An internal expansion card that

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Integrated sound hardware on PC motherboards

In the late 1990s many computer

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Architecture of Sound Card

Mixer receives inputs from both external connectors and

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Audio Codec

A single chip in soundcard
encodes analog audio as digital signals

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Device Driver

A low-level program that controls a device attached to a

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General Characteristics

It can be used in multimedia applications such as music

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Example

Enjoy multi-channel cinematic sound
Many sound cards come with 5.1 channel outputs

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Example

Independent input sources
Many sound cards come with independent line-in and microphone

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Example

Control and customize your audio
Many sound cards come with audio processing

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Audio Performance
Sample Rate：
11.025 kHz (Speech) 22.05 kHz (Music) 44.1

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Connectivity
Input：line in jack, microphone in jack
Output： headphone, mono, 2

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Processor
CODEC (Dependent of CPU, Cheap)
DSP(Independent of CPU)

Quality Parameters

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What is MIDI?
MIDI (Musical Instrument Digital Interface): a technology to synthesize

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There are actually three components in MIDI standard, which are the

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The MIDI protocol is an entire music description language in binary

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MIDI connector is a 5-pin DIN connector used to send MIDI

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When MIDI messages are stored on disks, they are commonly saved

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Sequencer is the key component for MIDI music creation.
A MIDI Sequencer

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Example

Drum sample 1

Drum sample 2

Bass sample 1

Bass sample 2

A combination of

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Audio Processing Software
(formerly Cool Edit Pro)
Audio Editing
Audio Effects
Multitrack Processing
Burning Audio

History

1990s, Syntrillium Software, Cool Edit,
2003, Adobe purchased Cool Edit Pro, Adobe

Creative Cloud

With the introduction of Creative Cloud branding, Adobe's licensing scheme

Download and install apps
Sync files and folders
Add fonts

Search for assets

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Workspace

A View buttons and toolbar B Editor panel with zoom navigator

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Waveform and Multitrack Editors
To edit individual files, use the Waveform Editor.

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Workspace

A Navigator B Timeline Ruler C Waveform Display D Spectral Display
E

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Waveform Display
Quiet audio has both lower peaks and lower valleys than

Spectral Display
This view lets you analyze audio data to see which

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Zoom audio
Zoom into a specific time range
In either the zoom navigator

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Workspace

Navigating time and playing audio
Navigate by scrolling
Navigate with the Selection/View panel
Current-time

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Importing, recording, and playing

Connecting to audio hardware
Configure audio inputs and outputs
Choose

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Importing, recording, and playing

Creating and opening files
Create a new, blank audio

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Importing, recording, and playing

Recording audio
You can record audio from a microphone

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Importing, recording, and playing

Monitoring recording and playback levels
To monitor the amplitude

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Importing, recording, and playing

Adjust recording levels for recording device
Adjust levels

Editing Audio

Selecting audio for playing, copying, cutting, (mix)pasting, and deleting
Select

Editing Audio

Remove artifacts automatically
For the quickest repair of small, individual

Editing Audio

Adjust amplitude using amplitude control
By default, the visual amplitude

Editing Audio

History Panel
The History panel lets you instantly revert back

Editing Audio

EDIT>Converting sample types
Convert the sample rate of a file
Convert

Exercise1 of Edit Audio

Steps
Open ex1File1 and ex1File2
Find and Copy “did” in

Editing Audio

Working with markers using mark panel
Markers (sometimes called cues)

Editing Audio

Playlists
A playlist is an arrangement of marker ranges

Applying Effects

Apply individual effects
From any submenu in the Effects menu,

Applying Effects

Apply groups of effects
The Effects Rack lets you insert, edit,

Applying Effects

About process effects
These processing-intensive effects can be applied only individually,

Applying Effects

Use effect presets
Many effects provide presets that let you store

Applying Effects

Generate a simple waveform
Choose Effects > Generate > Tones

Applying Effects

Generate Noise
Generating noise is useful for creating soothing sounds like

Applying Effects

Reverb effects
In a room, sound bounces off the walls, ceiling,

Applying Effects

Background Noise Reduction
The Noise Reduction effect dramatically reduces background and

Exercise3 of Noise Reduction

Steps
Create audio file
Record “I finished my work on

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Mixing multitrack sessions

The Multitrack Editor can mix together multiple audio tracks

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Mixing multitrack sessions

Create a new multitrack session
Template: specify source files and

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Mixing multitrack sessions

Insert an audio file into a track
Place CTI at

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Mixing multitrack sessions

Session (*.sesx) files
Adobe Audition save multitrack sessions in session

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Mixing multitrack sessions

A Track controls B Zoom navigator C Vertical scroll

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Mixing multitrack sessions

Arranging and editing tracks
Add or delete tracks
Name tracks
Move tracks
Mute

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Mixing multitrack sessions

Editing multitrack clips
Move a clip
Copy a clip
Remove a selected

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Mixing multitrack sessions

Export multitrack mixdown files
After you finish mixing a session,

Exercise 4 of Sound Remove

Steps
Mix cough with music in multitrack
Remove

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Multitrack routing

Buses, sends, and the Master track let you route multiple

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Mixing multitrack sessions

Audio tracks
Audio tracks contain either imported audio or

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Mixing multitrack sessions

Assign audio inputs and outputs to tracks
In the Inputs/Outputs

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Mixing multitrack sessions

Bus tracks
With bus tracks, you can combine the

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Mixing multitrack sessions

Sends
Sends let you route audio from a track

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Mixing multitrack sessions

Master track
The Master track , which is the

Exercise 5 of Multitrack routing

Ex4.mp3

Clip1

Clip2

Clip3

Clip4

Bus A

Master

Bus B

reverb

delay