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Audio Signals

Music Acoustics

Speech

Processing

Audio Signals (音频信号)

               Not only those we can hear.

      Audible Signal (可闻声)

     Sound Threshold of Pain

    Description

          Frequency: Number of Sound Period per second.

          Period: Duration of one Vibration.

          Speed: 

                       V_{in dry air} = 331.5 + 0.6T_c (m/s)

                       V_{in water}  = 1482 (m/s)  , 20 ^oC

                       V_{in sea water} = 1522 (m/s),  20 ^oC

                       V_{in glass} = 5640 (m/s)

                       V_{in steel}  = 5960 (m/s)

          Power(声功率): The energy emitted by

                                   sound source  per second.

          Intensity(声强): The Energy flow across a

                                   unit area.

          Pressure(声压): The Pressure on a unit area.

          Power Level (声功率级):

                L = 10 log( W/W₀)

          Intensity Level (声强级):

                L = 10 log( I/I₀)

          Pressure Level (声压级):

                L = 20 log( P/P₀)

                   ( P ²  = I ρ c )

                 Reference Power:      W₀ = 10^-12   (Watt)

     Reference Intensity:    I₀  = 10^-12  (Watt/m²)

                 Reference Pressure:   P₀ = 2x10^-5  (Pa)

     Sound Superposition

          W_Total = W₁  + W₂

           I _Total  =  I₁  + I₂

          P_Total   = sqrt(P₁ ²  + P₂ ² )

Music Acoustics

       Pitch(音调):    The perceived frequency by

                               human ear.

       Timbre(音色): The distinct characteristics

                               describing perceptual

                               qualities of sound.

       Brightness(明亮度): A quality of sound which

                                         relates to the proportion of

                                         the energy distributed over

                                         high frequencies.

       Rhythm/Tempo(节奏): Pattern of the beat

                                            combination

       Melody(旋律):   A set of tones structured together.

Speech

       Vocal Cord(声带): 

           Two small bands of muscle within the

            larynx(喉) that vibrates to produce the voice.

       Vocal Track(声道):

         The path that voice passed before it comes

            out of mouth.

       Formant(共振峰):  

           A characteristic acoustic resonance.

Processing

     Analysis: Extract the ID of Sound.

             Computational Auditory Scene Analysis

              Instrument Modeling

              Vocal Track Modeling

              Room Acoustics

                   (Sound Propagation + Psychoacoustics)

     Recognition: Understand the sound by known ID.

              Music Automatic Transcription

              Voice Recognition

     Synthesize: Make Machine Sing/Talk.

              MIDI

     Compression: Data file is too Fat for Secure and

                                    Effective transmission, Online or

                                    Wireless.

             CD, MP3, RM, WMA, AIFF

    Audio Device:

            Microphone (Dynamic, Condenser, Ribbon )

            Recorder

            Storage Media (Tape, MD, LD, CD...)

            Player

            Speaker