Digital Television & Home Theater • Audio for Video • Basic Acoustics • How & Why We Hear • Movie & Home Theater Sound-System Configurations, Including Surround Sound • Digital Audio Formats: the Good, the Bad, and the Sublime.
Sound Basics: What Is Sound? • Sound = Traveling Waves Of Air Pressure • Air Pressure Wave: Localized, Temporary, Sequential Increase + Decrease in Air Pressure Around Normal (15 lbs./sq. inch) • Each Wave Must Have Both A Positive (pressure increase) And Negative (pressure decrease) Part • Overall Air Pressure Cannot Change • Think Of Air Molecules Temporarily Bunching Up In Some Places and Spreading Out In Others. The Bunching Up Spreads Like Falling Dominos
Sound Basics: Frequency • A Sequential Increase & Decrease In Pressure Is Called A Cycle. • Think of It As A Single Wavelet. • A Cycle Takes A Finite Time To Complete • Pressure Variation Goes 0 + 0 - 0, or 0 - 0 + 0 • Sustained Sounds With Repetitive Identical Cycles Have An Associated Fundamental Frequency, F • F = The Number Of Cycles Occurring Within A Second Of Time • Expressed in Hz. = Cycles/Second
Sound Basics: Auditory Perception • When Sustained Sounds With Repetitive Air Pressure Waves Are Perceived By The Ear, They Give The Sensations Of Pitch & Loudness • More Cycles In A Given Span Of Time = Higher Pitched Sound • The Greater The Increase & Decrease In Air Pressure Variation Within Each Cycle = The Louder The Sound
Sound Basics: Hearing Range • Pitch Is Perceived Logarithmically In Octaves • One Octave Increase = Doubling The Frequency • Human Hearing Covers 10 Octaves, From 20 Cycles/Second to 20,000 Cycles/Second • Everyday Sounds Are Usually 40 Cycles/Second to 12,000 Cycles/Second • The Critical Band For Speech Recognition is 500 Cycles/Second to 2,000 Cycles/Second
Sound Basics: Wavelength • Air Pressure Waves Travel ~ 1,130 ft./sec. • A Cycle Of Air Pressure Variation That Takes A Finite Time To Complete Therefore Spreads Out Across a Finite Distance = It’s Wavelength • Sustained Sound With Repetitive Identical Cycles Having Fundamental Frequency F, Have Wavelength L Derived By: L Ft./Cycle = 1.13 Ft./Millisecond / F Cycles/Second • Note That The Higher The Frequency (& Pitch), The shorter The Wavelength
Resonation & Perception • Several Air Pressure Waves Simultaneously Traveling Through The Same Space Will Add Together Linearly. • So Will Traveling Air Pressure Waves When Trapped Between Two Physical Parallel Boundaries. • At Each Boundary Some Sound Passes Through But Most Bounces In The Reverse Direction • The Waves Will Continue To Bounce Back And Forth Between Boundaries Until All The Sound Has Leaked Out. • Sustained Sounds Will Continually Feed New Air Pressure Waves To Bounce And Add Together Between The Boundaries
Sound(Air Pressure)- Waves Trapped Between Parallel Walls Of A Resonator Sound Leakage
Resonation & Perception • For Most Frequencies, Multiple Bouncing Pressure Waves Will: • Momentarily Reinforce Each Other Some Places • Momentarily Oppose Each Other At Other Places • But With No Consistent Pattern.
Resonation & Perception • However, At A Few Frequencies Bouncing Pressure Waves Will Constantly Reinforce Each Other And Always At The Same Places • These Places Of Constantly Reinforcing Pressure Waves Are Called “Standing Waves”. • As Standing Waves Build In Intensity With Sustained Sound, More Sound “Leaks” Through The Boundaries To The Outside Until Equilibrium Is Reached.
1 2 Long-Term Average 3 Standing Waves
Resonation & Perception • Which Frequencies Will Produce Standing Waves? • Only Those For Which The Distance Between Boundaries Is An Integer Multiple Of The Frequency’s Wavelength • I. E. When 1, 2, 3, 4, ... Wavelengths Will Perfectly Fit Between The Boundaries With No Pieces Left Over.
Resonation & Perception • Parallel Physical Boundaries Therefore Act As A Resonator & Filter. Put Sustained Broadband Noise In (Which Contains Many Frequencies): • Most Frequencies Will Be Attenuated. • A Few Will Be Strengthened and Projected. • The Frequencies That Are Strongly Resonated Reveal The Dimensions Of The Resonator.
Resonation & Perception • Real-World Hollow Objects Are 3-Dimensional & Have Many Non-Parallel Boundaries • Standing Waves Occur At Many More Frequencies And Vary In Strength. • Putting In Sustained Broadband Noise Will Result In Highly Unique And Complex Spectrum Of Resonated Frequencies: A Spectral Fingerprint Of The Physical Object! • Strong Survival Value In Discriminating How Strongly Each Frequency (Out Of A Broad Range Of Frequencies) Is Being Reinforced By An Object.
Resonation & Perception • Our Ears Are Spectrum Analysers • Inner Ears Compare Strengths Of Different Frequencies Coming From A Single Object. • We Can Associate Sounds We Hear With Objects We See, Even When We Can’t See Them! • Our Ears Report To Our Brains, Which Is Not Aware Of Separate Frequencies, But Instead Perceives Timbre - An Overall Sound Quality.
The Purpose of Hearing • Scout Out Our Environment (for Predators and Food) Beyond Our Line Of Sight. • What is out there?! • Is It Moving Closer Or Further Away?! • Where Is It?!
How We Hear • What Is Out There? • Spectral analysis with either/both ears. (Previously explained)
How We Hear • What Is Out There? • Spectral analysis with either/both ears. (Previously explained.) • Is It Moving Closer Or Further Away? • Changes in volume with either/both ears. (Inverse Square Law.)
How We Hear • Where Is It? • Bianural Hearing: Comparing the same sound as heard by two physically separate, distinctly shaped ears: • Relative Loudness • Time Of Arrival • Head-Related Transfer Function
How We Hear • Where Is It? • Two Separate Perceptions of Environmental Sound • Localization - I can point to the direction of the sound (e.g a lion’s roar) • Envelopment - I am inside the sound (e.g. rain & thunder)
How We Localize Sound What’s The Difference? Head-Related Transfer Function
Hi Fidelity/Home Theater Audio • To Simulate Nature It Must Reproduce • Realistic Complex Acoustic Spectrum • Accurate Full-Range Speakers • High-End Electronics • Realistic Volume Levels/Volume Changes • Sufficient Power and Speaker Sensitivity • Accurate, Clean Micro and Macro Dynamics • Realistic Binaural Cues via Multiple Speakers: • Relative Loudness • Time Of Arrival • Head-Related Transfer Function
Hi Fidelity/Home Theater Audio • Monophonic Sound: • All sound sources sonically image at the speaker.
Hi Fidelity/Home Theater Audio • 2-Channel Stereophonic Sound: • Sound sources sonically phantom-image between and behind the speakers. • Can have multiple simultaneous sonic phantom images. • Can smoothly pan a sonic phantom image. • 2 Discrete Channels
Hi Fidelity/Home Theater Audio • Quadraphonic Sound • Sound sources sonically phantom-image between the front speakers, between the back speakers, but not between the side speakers. • 4 -> 2 Matrixed Channels and barely feasible Discrete
Hi Fidelity/Home Theater Audio • Matrixed 4 Channels into 2 • 2 Channels – Lt & Rt provide: • Left Channel = Lt • Right Channel = Rt • Channel 3 = Lt + Rt • Channel 4 = Lt - Rt • Just 3 db Channel Isolation due to Inter-channel Bleeding. • Steering Logic Can Isolate Channels Further, But for Only One Phantom Image at a Time
Hi Fidelity/Home Theater Audio • Dolby Stereo (Theaters) Thanks, Star Wars Episode 4 • Left/Center/Right Speakers Behind Screen + Single Surround Channel into Many Speakers for Envelopment • 4 -> 2 Matrixed Channels. Delayed, Frequency-Limited Surround Channel
Hi Fidelity/Home Theater Audio • Dolby Pro Logic (Home) • Left/Center/Right w. Center Above/Below the Display + Single Surround Channel into 2 Dipolar Speakers for Envelopment • 4 -> 2 Matrixed Channels. Delayed, Frequency-Limited Surround Channel
Hi Fidelity/Home Theater Audio • Digital 5.1 in Theaters • Left/Center/Right Speakers Behind Screen + Left Sur/Right Sur + Subwoofer • Discrete 5 Full-Range Channels + Discrete Subwoofer
Hi Fidelity/Home Theater Audio • Digital 5.1 – Home Configuration • Left/Center/Right w. Center Above/Below the Display + Left Sur/Right Sur + Subwoofer -30o 0o +30o -120o +120o • Discrete 5 Full-Range Channels + Discrete Subwoofer
Hi Fidelity/Home Theater Audio • Digital 6.1 in Theaters Thanks, Star Wars Episode 1 • Left/Center/Right Behind Screen + Left Sur/Back Sur/ Right Sur + Subwoofer • 5 Channels Discrete + Subwoofer + Back Channel Matrixed
Hi Fidelity/Home Theater Audio • Digital 7.1 – Home Configuration • Left/Center/Right w. Center Above/Below the Display + Left Sur/Left Back/Right Back/Right Sur + Sub -30o 0o +30o -90o +90o -150o +150o • Discrete 7 Full-Range Channels + Discrete Subwoofer
Digital Television • It’s Coming February 17, 2009. Do you know where your programs are?
Digital Television What Is It? • A Totally New Television System
Digital Television What was wrong with the old Analog system?
Digital Television What was wrong with the old Analog system? • 1930’s Technology
Digital Television What was wrong with the old Analog system? • 1930’s Technology • Black & White
Digital Television What was wrong with the old Analog system? • 1930’s Technology • Black & White • Monophonic Sound
Digital Television What was wrong with the old Analog system? • 1930’s Technology • Black & White • Monophonic Sound • Maximum Screen Size: 19 inches
Digital Television What was wrong with the old Analog system? • 1930’s Technology • Black & White • Monophonic Sound • Maximum Screen Size: 19 inches • Kluged Retrofits: Still not close to photographic and larger-than-life quality of movies.