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Audio Sound Audio synthesis Audio Perception Sound: Pressure waves in frequencies between 50Herz - 22,000Herz Lower frequencies more felt by the whole body than heard Sounds can be perceived as coming from a location Not terribly accurate Cone of confusion 3D Audio Perception

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audio

Audio

Sound

Audio synthesis

IAT 410

audio perception
Audio Perception
  • Sound: Pressure waves in frequencies between 50Herz - 22,000Herz
  • Lower frequencies more felt by the whole body than heard
  • Sounds can be perceived as coming from a location
    • Not terribly accurate
    • Cone of confusion

IAT 410

3d audio perception
3D Audio Perception
  • Cone of confusion
    • Cone-shaped zones in front of and behind head
  • 3D Audio cues:
    • Interaural Time Difference
    • Interaural Intensity Difference
    • Pinnae filtering
    • Body filtering

IAT 410

3d audio perception4
3D Audio Perception
  • Goal for 3D sound is “Spatialization”
  • The sense that the
    • Sound originates outside your head
    • Sound has a direction
  • Interaural Time Difference
    • The more extremely left or right, the greater the difference
    • Time difference < 5ms

IAT 410

3d audio perception5
3D Audio Perception
  • Interaural Intensity Difference
    • Head absorbs and reflects sound energy
    • The first ear to get sound gets loudest sound
    • “Head Shadow”
  • Cone of confusion:
    • Time difference too small to detect
    • Intensity is similar in both ears

IAT 410

pinnae filtering
Pinnae Filtering
  • Outer ear (Pinna) shape filters sound based on its direction
  • Childhood learning trains brain to associate filtering effects with direction
  • Unique per person
  • Record directional white noise
    • Microphone in ear canal
    • Sounds from speakers located about head

IAT 410

pinnae filtering7
Pinnae Filtering
  • A “Generic” Pinna can be simulated
  • Record directional white noise received by dummy head
  • Body filtering
    • Reflection and absorption
    • Included in Pinna model

IAT 410

head related transfer function
Head-Related Transfer Function
  • HRTF is the general term
  • Transformation of “real” sound to spatialized sound
  • Best delivered by earphones

IAT 410

environmental effects
Environmental Effects
  • Sound exists in an environment
    • Bounces off objects
    • Is absorbed by objects
  • Simple effects
    • Reverb: Simulate the environmental echo
      • Echo is the attenuated signal
      • Gives a richer room-like feeling
      • Larger room has longer time delay

IAT 410

audio signals
Audio signals
  • Nyquist limit:
    • Must sample signal at least twice as frequently as highest reproducible frequency
    • Audio: 44.1KHz (CD)
    • 22KHz
    • 11KHz (Analog AM Radio)
    • 8KHz (Telephone)

IAT 410

audio digital implications
Audio - Digital Implications
  • 44,100 Hz
    • 44,100 Samples/sec
    • 16-bit samples
    • Stereo
    • 172KBytes/sec
  • Specialized hardware - Sound card

IAT 410

reproduction
Reproduction
  • Sampling
    • Record sounds by whatever means
  • Synthesis
    • Analog Synthesis
    • FM Synthesis
    • Wavetable Synthesis

IAT 410

control
Control
  • MIDI - Musical Instrument Digital Interface
  • Developed to control music synthesizers
    • Details of synthesis are controlled by synthesizer
  • MIDI data
    • Sets synthesis parameters
    • Sets music sequence

IAT 410

synthesis
Synthesis
  • Analog Synthesis
    • Simple sum of frequencies
    • Select from a palette of source frequencies
    • Sum of frequencies is filtered
  • FM
    • One frequency is controlled by another
  • Wavetable
    • Digitize audio signals

IAT 410

analog synthesis
Analog Synthesis
  • Fourier’s observation
    • Any signal can be created as the sum of sine waves
    • Square wave: Infinite sum
    • f + 2f + 4f…
  • Synthesizer:
    • Collection of oscillators

IAT 410

frequency domain
Frequency Domain
  • A perfectly periodic signal plotted in the frequency domain

(Time domain plot)

IAT 410

spectrum
Spectrum
  • Spectrum represents the set of frequencies present in the signal

IAT 410

filters
Filters
  • Eliminate part of the signal by removing certain frequencies
  • Analog filters don’t have these “square” response shapes
  • Band pass
    • Bandwidth

IAT 410

fm synthesis
FM Synthesis
  • Modulate the frequency of a wave
  • Carrier frequency is modulated by Modulator signal

IAT 410

fm synthesis for synthesizers
FM Synthesis for Synthesizers
  • The greater the Modulator amplitude, the greater the Carrier frequency variation
    • Higher Carrier bandwidth
  • DX: Carrier and Modulator are “musically-tuned frequency”
    • Depends on the note you are playing
    • Controls the harmonic content of a note

IAT 410

wavetable synthesis
Wavetable Synthesis
  • Collect a sample of the real sound
  • Issues:
    • Reduce memory load by looping sample
    • Shift pitch instead of sampling each individual note
    • Apply interpolation techniques to make pitch shifting work right

IAT 410

audio path

Raw Sound

(Sample, FM, etc)

Tuned

MIDI

Note Sequence

Resampling

Audio Path

Reverb,

Environment.

Spatialization

Envelope

Loudness Control

Mixing/

Combination

IAT 410

wavetable synthesis example
Wavetable Synthesis Example
  • Leyanda (Guitar)
  • Leyanda (CDShaw)

IAT 410

interactive sound
Interactive Sound
  • Goal
    • Want to enhance the interactive experience
    • Give the user a sense of presence
    • Add to the emotional content of the game
    • Make it more fun

IAT 410

interactive sound25
Interactive Sound
  • Music
  • Sound effects
    • Noises
    • Commentary - Sports
  • Narrative
  • Conversations

IAT 410

interactive problems
Interactive Problems
  • Regular music composition has
    • Beginning
    • Middle
    • End
  • Interactive user control makes this difficult
    • Some genres have this structure

IAT 410

interactive music
Interactive Music
  • Game genres with order
    • Sports
    • Racing
    • Fighting
  • Semi-Ordered
    • Puzzle
    • Adventure

IAT 410

music genres
Music Genres
  • The Infinite Loop
    • Theme and variation plays forever
    • Pomp & Circumstance
    • Diablo
  • Problems:
    • 30 second piece repeated over 6 hours!
    • 720 repetitions!
    • Diablo example: 12 Repetitions/hour

IAT 410

repetition solutions
Repetition Solutions
  • Make the Dominant theme hard to find
    • No catchy theme!
    • Create a variety of textures
    • Make only transitions stand out
  • Where repetition is small
    • Don’t repeat musical phrases

IAT 410

music strategies
Music Strategies
  • Play Win or Lose music
    • Music must be long enough to be meaningful
    • Music may be so long that the game situation changes before completion
    • Very short music makes little sense
  • Interrupt current music
    • Sounds jarring

IAT 410

modules
Modules
  • Modular chunks
    • Each segment of the game plays independently of others
    • Some thematic relation
    • Disjointed

IAT 410

music strategies32
Music Strategies
  • Compose many themes in parallel
  • Switch between themes
  • Connect modular components together

IAT 410

analogy parallel trains
Analogy: Parallel Trains
  • N trains of music running in parallel
  • Each train serves an emotional purpose
    • Train A: Calm
    • Train B: Rising Excitement
    • Train C: Climactic moments
    • Train D: Falling Excitement
  • Generally, Train A would be most commonly played

IAT 410

within each musical train
Within Each Musical Train
  • Each “Car” contains a few bars of music
  • Switch between trains when a “Car” is complete
    • Don’t switch in the middle of a “Car”
  • Simple version:
    • Each musical phrase ends on last bar of “Car”
  • Complex:
    • Notes at end are carried over to next

IAT 410

parallel trains

Bars 1-8

Bars 1-8

Bars 1-8

Bars 1-8

Bars 9-16

Bars 9-16

Bars 9-16

Bars 9-16

Bars 17-24

Bars 17-24

Bars 17-24

Bars 17-24

Bars 25-32

Bars 25-32

Bars 25-32

Bars 25-32

Parallel Trains

IAT 410

parallel trains shuffle cars
Parallel Trains: Shuffle Cars
  • Shuffle cars
    • Instead of playing cars in order
  • Problem: Random cars sound like random radio tuning
  • Must determine
    • Appropriate car pairings
    • Reasonable paths

IAT 410

repetition in trains
Repetition In Trains
  • Use repeated phrases carefully
  • Maybe use a statistical tool to analyze paths
    • Bayesian nets
  • Endings:
    • Use transitions as an opportunity to “End”
    • Use next Car to “Begin” new series

IAT 410

composing a train
Composing a Train
  • Create a piece with all layers
    • Piece can probably survive a layer or two removed
    • Variation = piece with layer removed
  • Be careful with prominent instruments
    • Fallback: Use instruments with similar acoustical properties
      • Piano, Organ, Woodwinds
      • No Trumpets, Drums or Screaming guitar!

IAT 410