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Published byMarvin Williamson Modified over 8 years ago
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Dan Nichols Head of Recording Services Internet2 Multimedia Specialist Northern Illinois University Your TV IS TOO SLOW
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Your Everything is too slow….. -Cameras -Displays -Microphones -Networks
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The Human Condition & Digital Systems Your etc. IS TOO SLOW
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Nyquist & Pulse Code Modulation (1982) - Data Driven Compromise - Not Fault Tolerant - Fixed Clock - Good Frequency Correlation - Poor Transient Correlation Your etc. IS TOO SLOW Audio Comparisons
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Your etc. IS TOO SLOW Visual Comparisons
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-5ms Unison Impulse Window 221 Samples (44.1 KHz); less than 1/64 Note at 120 BPM -Video Frame Sync (-125 ms to 45 ms) ITU Recommendation; Film is +/- 22 ms Your etc. IS TOO SLOW Observable Latency Effects
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Positive Latency Spiral: -Player/Location A Plays Slightly Ahead -Audio Arrives Delayed at Location B (slightly) -Player/Location B Plays Slightly Ahead -Audio Arrives Delayed at Location A (slightly) -If players anticipation is reasonably synchronized with latency, both will feel ahead but the tempo and feel will stabilize -If either player is anticipates more than the latency, the tempo will continue to increase as the players attempt to maintain relative anticipation Your etc. IS TOO SLOW Latency Spirals
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Follow the Leader: - Player/Location A Plays Normally, Leading the Ensemble - Audio Arrives Delayed at Location B (slightly) - Player/Location B Plays in Unison with Player/Location A - Audio Arrives Delayed at Location A (more so) - Location B Receives Synchronous Musical Experience - Location A Experiences Consistent (perhaps tolerable) Lag Your etc. IS TOO SLOW Latency Spirals
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Negative Latency Spiral: -Player/Location A Plays Normally, In Accordance with Musical Instincts -Audio Arrives at Location B Delayed -Player/Location B Plays Synchronously with Location A -Audio Arrives at Location A Delayed -Player/Location A Plays Synchronously with Location B -Tempo Slows Until Collapse or Stabilization (Dirge) Your etc. IS TOO SLOW Latency Spirals
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Video Delay is Negligible/Nonexistent Audio Delay is Predictable: - 1 ms of Acoustic Delay Originates from 1 ft of Distance - 2.9 ms of Acoustic Delay Originates from 1 m of Distance - Delays from Reflective Surface Integrate into Direct Sound (Timbre-dependent) Under 40 ms - Haas Effect/Law of the First Wavefront - Everything Else is Considered Reverberation (Agreeable Delay) - Delays from Multiple Surfaces Produce Comb Filtering Your etc. IS TOO SLOW In the Real World…
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Sources of Latency Include: - Ingestion Latency - Transmission Latency - Reproduction Latency Your etc. IS TOO SLOW In Our Networked World…
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On Camera: Exposure Latency Double the Frame Rate/Halve the Latency Buffering/Processing Latency Collecting/Processing Frames into Compressed Output Audio Interfaces: Audio Buffer Size in Samples Double the Sample Rate/Halve the Latency Your etc. IS TOO SLOW Where Does It Originate?
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Ingestion/Reproduction: Motherboard Architecture Software Latency Compression Latency Reproduction Display Type Video Repeaters/Switchers/Converters Your etc. IS TOO SLOW Where Does It Originate?
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Microphones Selection & Placement: Place Microphones as Close to Sources as Possible Consider Analog Dynamic Compression Supplement Close Mics with Nearfield/Midfield Mics Baffle Reflections to Reduce Echo/Reverb Speaker Selection and Placement: Place Speakers where the Instruments would Naturally be Staged in an Ensemble or Live Performance Use Diffusive Speaker Placement for Diffusive Instruments & Directional Speaker Placement for Directional Instruments Consider Adding Reverb upon Reception of Remote Signal Your etc. IS TOO SLOW Practical, State-of-the-Moment Advice
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General Audio Considerations: Employ Analog Mixers/Analog Audio Inputs Use Multichannel Audio for Different Sources Replicate Source and Destination Input Levels Employ a dB Meter or Spectrograph Use the Acoustic Feedback Test to Verify Latency is within Interactive Thresholds Close one or both ends of the audio loop and listen for Echo-Delay Feedback or conventional Feedback Your etc. IS TOO SLOW Practical, State-of-the-Moment Advice
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Video Reproduction Considerations: Consider Video Reproduction Latency CRTs – Less than 8 ms LCDs/LEDs/OLEDs – Greater than 9 ms Projectors – 16 ms or Greater Disable Image Processing http://www.displaylag.com/display-database/ http://www.projectorreviews.com/the-art-of-gaming/ Position Low Latency Display in Natural Location Face Audience and Performers Capture Both Local and Remote Display for Local Projection/Display Repeat Video Signal after Local Reproduction Use Multiple Redundant Outputs on Local Machine for High Latency, Large or Switched Video Your etc. IS TOO SLOW Practical, State-of-the-Moment Advice
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Video Capture Considerations: Use Higher Frame Rates and Software Compression Higher Frame Rate can Reduce More Latency than Compression Adds Higher Frame Rates/Shutter Speeds will Require More Light Your etc. IS TOO SLOW Practical, State-of-the-Moment Advice
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Faster, More Robust Networks Faster Computers Higher Sample Rate, Fault-Tolerant/Redundant Audio DSD (22.6 Mbps) 192 KHz/384 KHz More Nimble Camera Designers Custom VTC Machine Vision Cameras https://www.ximea.com/en/products/oem-custom-cameras PTZ Control http://www.bhphotovideo.com/c/product/1133719- REG/syrp_0032_0001_genie_mini.html http://www.bhphotovideo.com/c/product/1170815- REG/cinetics_cinetics_axis360_pan_and.html/prm/alsVwDtl http://www.bhphotovideo.com/c/product/1187283- REG/cobracrane_ptu_proline_pan_tilt_head.html/prm/alsVwDtl Lower Latency Displays http:// intelextrememasters.com / Your etc. IS TOO SLOW Development Vectors
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