🗊Презентация Basic of Digital Audio

2.1 Basic of Digital Audio Basic of Sound

How sound waves interact When two or more sound waves meet, they add to and subtract from each other.

Sound Frequency

2.2 Audio Digitalization Audio signals Analog Signal: an electrical representation of sound originated by microphone, tape head. Loudspeakers or headphones convert an electrical audio signal into sound. Digital Signal: a discrete-time signal for which not only the time but also the amplitude has discrete values

Lifecycle of sound in Multimedia System

Procedure of audio digitalization

Procedure of audio digitalization

Understanding sample rate

Understanding bit depth

dB(Decibel)

dBFS(dB relative to full scale)

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

2.3 Audio File Format An audio file format is a file format for storing digital audio data on a computer system. An audio file usually contains a header indicating sample rate, bit depth etc(metadata), and then a large number of digital audio data.

Format types The bit layout of the audio data (excluding metadata) is called the audio coding format and can be uncompressed. It is important to distinguish between audio file(container) format and audio coding format. A coding format and a file format are usually defined in one compression standard, so most audio file formats support only one type of audio

Typical Audio File Formats *.WAV Standard audio file container format used mainly in Windows PCs. Commonly used for storing uncompressed (PCM), CD-quality sound files (large in size). (see music.wav) *.MP3 Defined in MPEG-1 Audio Layer-3. It is the most common sound file format used today.(Not to be confused with MPEG-3.) *.AAC Part of MPEG-2 and MPEG-4. Designed to be the successor of the MP3 format. Default file format for YouTube, iPhone, iPod, iPad, iTunes etc. *.WMA(Windows Media Audio) owned by Microsoft. Designed with Digital Rights Management (DRM) abilities for copy protection. *.OGG A patent-free, open source container format supporting a variety of coding format *.APE For a lossless audio compression format. Take up several times as much space as lossy compression formats. (see CDImage.ape)

DRM Dataflow Diagram

2.4 Digital Audio Acquisition and Processing Audio Acquisition

2.5 Digital Audio Compression Standards Introduction to Digital Audio Compression

Categories of Audio Compression Standards Lossless Compression less space without losing any information. compression ratio of about 2:1 Lossy Compression greater reductions in file size reduction in audio quality most standards offer a range of degrees of compression, generally measured in bit rate

Audio Compression Standards

Comparison between common audio formats

MP3 1993, MPEG-1 Audio Layer III a digital audio coding format which uses a form of lossy data compression more commonly referred to as MP3 designed by the Moving Picture Experts Group (MPEG) as part of its MPEG-1 standard and later extended in the MPEG-2 standard. Compared to CD quality digital audio(44kKz, 16bit), MP3 compression commonly achieves 75 to 95% reduction in size. CD:1.4Mb/s, MP3:128Kb/s

2.6 Sound Card and Electroacoustic Equipment Sound Card An internal expansion card that facilitates input and output of audio signals to and from a computer under control of computer programs..

Integrated sound hardware on PC motherboards In the late 1990s many computer manufacturers began to replace plug-in soundcards with a "codec" chip integrated into the motherboard. The integrated sound system is often still referred to as a "sound card". The best plug-in cards, which use better and more expensive components, can achieve higher quality than integrated sound.

Architecture of Sound Card

Audio Codec

Device Driver

General Characteristics It can be used in multimedia applications such as music composition, audio editing, presentation, education, entertainment (games) , etc

Example Enjoy multi-channel cinematic sound Many sound cards come with 5.1 channel outputs so you can connect to your existing multi-channel speakers with ease.

Example Independent input sources Many sound cards come with independent line-in and microphone connectors, which allow you to plug in two different audio sources to your PC. You can plug in your MP3 player and sing along, while recording your singing session for your friends to enjoy!

Example Control and customize your audio Many sound cards come with audio processing software, which is designed to bring cinematic difference to home theatre PCs! You can also adjust the level of immersion you like, simply by adjusting the sliders on Control Panel.

Quality Parameters Audio Performance Sample Rate： 11.025 kHz (Speech) 22.05 kHz (Music) 44.1 kHz (Hi-Fi) Bit Size： 8 bits/256 (Speech) 16 bits/65 536 (Hi-Fi) SNR(Signal-to-noise ratio)：>80db

Quality Parameters Connectivity Input：line in jack, microphone in jack Output： headphone, mono, 2 channels(Stereo)、2.1/4.1/5.1 Channels (Surround)

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

2.7 Electric Music and MIDI What is MIDI? MIDI (Musical Instrument Digital Interface): a technology to synthesize music using electronic equipment. MIDI Standards An industry-standard that enables electronic musical instruments, computers and other electronic equipment to communicate and synchronize with each other.

MIDI Working Progress

MIDI Protocol (language) The MIDI protocol is an entire music description language in binary form like CPU machine language instructions for musical instruments. . MIDI language carries event messages that specify notation, pitch and velocity, control signals for parameters such as volume, vibrato, and etc.

MIDI Connector MIDI connector is a 5-pin DIN connector used to send MIDI messages . A single MIDI link can carry up to sixteen channels of information, each of which can be routed to a separate device. So MIDI allows multiple instruments to be played from a single controller which makes stage setups much more portable.  

MIDI File When MIDI messages are stored on disks, they are commonly saved in the Standard MIDI file format. MIDI file does not contain the actual sound, but only commands(like musical notation) to make the sounds, so it use a thousand times less disk space than the equivalent recorded audio.

MIDI Sequencer Sequencer is the key component for MIDI music creation. A MIDI Sequencer (or simply sequencer) is a device or application software that can record, edit, or play back music, by handling note and performance information in MIDI

Example

2.8 Adobe Audition Audio Processing Software (formerly Cool Edit Pro) Audio Editing Audio Effects Multitrack Processing Burning Audio CD

History

Creative Cloud

Creative Cloud for desktop

Workspace

Workspace Waveform and Multitrack Editors To edit individual files, use the Waveform Editor. To mix multiple files and integrate them with video, use the Multitrack Editor. The Waveform and Multitrack editors use different editing methods, and each has unique advantages.

Waveform Display Waveform Display Quiet audio has both lower peaks and lower valleys than loud audio. Channels can be viewed as layered or uniquely colored. View > Waveform Channels

Spectral Display Spectral Display This view lets you analyze audio data to see which frequencies are most prevalent. Brighter colors represent greater amplitude components. Colors range from dark blue (low-amplitude frequencies) to bright yellow (high-amplitude frequencies). The spectral display is perfect for removing unwanted sounds, such as coughs and other artifacts.

Zoom audio Zoom audio Zoom into a specific time range In either the zoom navigator or the timeline ruler, right-click and drag Extend or shorten the displayed range Drag the left or right edge of the highlighted area in the zoom navigator Using zoom button in the Editor panel

Workspace

Importing, recording, and playing

Importing, recording, and playing

Importing, recording, and playing

Importing, recording, and playing

Importing, recording, and playing

Editing Audio

Editing Audio

Editing Audio

Editing Audio

Editing Audio

Exercise1 of Edit Audio

Editing Audio

Editing Audio

Applying Effects

Applying Effects

Applying Effects

Applying Effects

Applying Effects

Applying Effects

Applying Effects

Applying Effects

Exercise3 of Noise Reduction

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Exercise 4 of Sound Remove

Multitrack routing

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Mixing multitrack sessions

Exercise 5 of Multitrack routing

Summary ☆Audio Digitalization, Music Symbolization ☆Three Essentials of Digital Audio, Audio File Formats ☆Digital Audio Compression Standards and Software ☆Sound Card and Electroacoustic Equipment ☆Electric Music and MIDI ☆Audio Processing Software: Audition