TV Tech Basics for NonLinear Editors GVExpo 2006
TV Tech Basics for Non-Linear Editors GVExpo 2006 Eric Wenocur Lab Tech Systems Silver Spring, MD eric@lab-tech-systems. com
Tutorial Overview § Elements of a Non-Linear Editing System § Monitors, Scopes and Video § Mixers and Audio § Videotape Machines § Simple Troubleshooting 2
Typical NLE System Video Mon & Scopes Speakers Mixer VTR NLE Storage 3
System Engineering Perspective § Maintain Signal Quality § Accurate Monitoring § What is the signal really like? § How will it look/sound elsewhere? § Flexibility 4
Monitors, Scopes & Video Top Four Mistakes or Misconceptions 5
Monitors, Scopes & Video Top Four Mistakes or Misconceptions 1) Adjusting the monitor to make the picture look “right” 6
Monitors, Scopes & Video Top Four Mistakes or Misconceptions 1) Adjusting the monitor to make the picture look “right” 2) Lack of colorbars at head of tape or sequence 7
Monitors, Scopes & Video Top Four Mistakes or Misconceptions 1) Adjusting the monitor to make the picture look “right” 2) Lack of colorbars at head of tape or sequence 3) Program not referenced to Bars 8
Monitors, Scopes & Video Top Four Mistakes or Misconceptions 1) Adjusting the monitor to make the picture look “right” 2) Lack of colorbars at head of tape or sequence 3) Program not referenced to Bars 4) Incorrect levels and other errors in the picture 9
Why Bars & Tone Matter! How does anyone know what YOUR show is supposed to look like? And furthermore… How does anyone know what ANYTHING is supposed to look like? 10
Why Bars & Tone Matter! § We know what colorbars are supposed to look like (they have been defined by Standards). § Establish a known reference for Content (which includes the conditions at the time) § Use for setting up tape playback to produce the desired result § Useful for verifying properation of equipment and systems 11
The Monitor as a Tool § Apply a known good signal § Set up the monitor § Leave it alone! 12
Simple Monitor Setup § Use known correct SMPTE Bars (composite) § Set desired ambient light § Set controls back to Presets § Adjust brightness (black level) for correct Pluge § Adjust chroma and phase in “blue gun” mode § Set contrast for moderate intensity 13
Where to get test signals? § Facility test generator § Non-linear editor § Many newer VTRs § Professional cameras 14
Other Monitor Controls 15
So… How do we know if the TEST SIGNAL is good? 16
Waveform Monitor/Vectorscope Conventional & Rasterizing 17
Waveform Monitor & Vectorscope § Measure luminance and chrominance levels § Find appropriate black or white levels, appropriate saturation, check hue § Display color-balance information (for color-correction) § Find flaws in video, track down system problems 18
Waveform Monitor 19
Vectorscope 20
Recommended Levels Using composite scopes… § Keep luma between 7. 5 and 105 ire § Keep chroma between -20 and 100 ire § Rules are most stringent for conventional broadcasting and anything on satellite § Use common sense… 21
Typical NLE Video Signal Path VTR NLE Signals could be composite, Y/C component, SDI… 22
Video Signal Formats “F” Cable: RF (cable TV) RGB Set: Component Analog BNC Cable: Analog & Digital Video Y/C Cable: S-Video 23
Critical Video Connection Rules § Video signal lines must terminate in 75 -ohms at the end of the run! § You cannot passively “split” or “combine” video signals! § You can passively “loop” signals between devices, but must terminate at end! 24
Possible NLE Video Signal Path Mon A B Term VTR NLE Note: VTR signal loops through monitor 25
Typical Monitor Rear View 26
Some Common Video System Problems § No termination or double-termination (watch those switches and terminators) § Two signals feeding same input (improperly using passive loop-thrus) § Component cable mixup (Y, R-Y, B-Y) § Component mode error (YRB vs. RGB) 27
Video Unterminated 28
Video Double-terminated 29
Component Cable Mixup Correct R-Y & B-Y Swapped 30
A few words about Reference, Genlock and Timing § Reference signals are used to make equipment produce output signals in sync with each other. § Reference is about playback, not recording; the recording device always locks to its input signal. § To “genlock” means locking a device to a reference signal. § “Timing” is about the relationship between two devices that both feed a third device (such as cameras feeding a switcher). § There is NO “timing” in a standalone NLE system! § Having devices locked to a common reference is highly recommended, but not critical in most cases. 31
Mixers & Audio Top Three Mistakes or Misconceptions 32
Mixers & Audio Top Three Mistakes or Misconceptions 1) Incorrect signal levels between equipment 33
Mixers & Audio Top Three Mistakes or Misconceptions 1) Incorrect signal levels between equipment 2) Monitoring incorrect or mixed-up signals 34
Mixers & Audio Top Three Mistakes or Misconceptions 1) Incorrect signal levels between equipment 2) Monitoring incorrect or mixed-up signals 3) Distortion and other problems in audio 35
Basic Mixer Sections § Input Channels Process signals entering mixer (input jacks, mic preamp, equalizer, channel fader) § Buses & Outputs Combine signals together and send out (bus assign, bus master level, output jacks) § Monitoring Controls speaker volume and what is heard (mon source select, speaker volume) 36
Basic Mixer Sections Aux Bus Masters & Misc. Monitor Section Output Bus Masters Input Channel Strips 37
Mixer Flow #1 Input Channels Buses Outputs 38
Mixer Flow #2 Input Channel Aux Send with Pre/Post Select Buses & Outputs 39
Mixer Flow #3 Added Monitor Section 40
Issues with Audio Connectors § The same types of connectors are often used for different types of signals (eg: XLRs for both mic and line level). § Some connectors look similar but aren’t (eg: 2 - and 3 -conductor phone plugs). § Preponderance of unbalanced “consumer” connectors (RCA phono plug) on gear. 41
Common Audio Connectors Phone plugs XLR plugs Terminal Block Mini plug RCA plug 42
Audio Operating Level § There are roughly three categories of audio operating level: Mic, Line and Speaker. § “Line” has a wide range of levels in use between equipment. § Professional equipment line levels are typically 10 -20 d. B higher than consumer or “prosumer”. § Pro level is often referred to as “+4” Consumer level is often known as “-10” § It is not wise to connect these devices together without proper interfacing to compensate! 43
Connectors & Signals Chart 44
Typical Mixer Connections Main Bus Outs Tape CR Sub Ins/ Mon Bus Outs Aux Sends Input Channels Channel Insert Line Input Mic Input 45
A Word about Phantom Power § 48 volts DC used to power condensor microphones § This voltage can damage other equipment. § Unless you are using a condensor mic LEAVE IT OFF! 46
Possible NLE Audio Signal Path Mixer Monitoring Output Buses Input Channels VTR NLE 47
VTR to Mixer to NLE Mixer Monitoring Output Buses Input Channels VTR NLE 48
NLE to Mixer to VTR Mixer Monitoring Output Buses Input Channels VTR NLE 49
Possible NLE Audio Signal Path Mixer Monitoring Output Buses Input Channels VTR NLE 50
Interfacing Consumer Gear Mixer Monitoring Output Buses Input Channels VHS Use TAPE Outs to feed VHS or DVD-R (same signal as Main Outs but correct level) 51
Audio Metering Why does the same audio look different on different meters? 52
Uh oh… 53
Audio Metering § Mechanical analog or bargraph? § Where is “ 0”? Different for analog and digital applications. § How large is the scale range? Meters vary from 23 d. B to 60 or 80 d. B scales. § How quickly does the meter respond to changes in audio? Ballistics can be average, peak, PPM, etc. 54
Audio Metering Analog § Analog audio will distort when level is too high, but the effect is usually gradual. § Analog meters were designed to show average levels around 0 VU. § There is usually 10 -20 d. B left above 0 VU before distortion. § Tone should be at 0 VU. 55
Audio Metering Digital § Digital audio has an absolute upper limit which is called Full Scale. § Digital meters read in terms of d. BFS (decibels under Full Scale) § Maximum possible level is at 0 d. BFS. § Tone is usually at about -20 d. BFS so there is 20 d. B of headroom before overload. 56
Typical Audio Flaws § Clipping and other distortion § Excessive noise beneath audio § Tonal imbalance § Channel phase reversal § Audio/video lip-sync errors 57
Balanced and Unbalanced Connections § This has nothing to do with “sonic balance. ” § Balanced audio connections cancel out noise picked up on the cable. § Balanced typically uses two signal wires and a shield, connectors have three terminals. § Balanced is usually also “pro” (+4) level. § You can connect balanced and unbalanced together but it requires knowledge! 58
Videotape Machines Top Four Mistakes or Misconceptions 59
Videotape Machines Top Four Mistakes or Misconceptions 1) Wrong format / wrong deck 60
Videotape Machines Top Four Mistakes or Misconceptions 1) Wrong format / wrong deck 2) Failure to begin with controls in PRESET 61
Videotape Machines Top Four Mistakes or Misconceptions 1) Wrong format / wrong deck 2) Failure to begin with controls in PRESET 3) Failure to set up playback to Bars 62
Videotape Machines Top Four Mistakes or Misconceptions 1) Wrong format / wrong deck 2) Failure to begin with controls in PRESET 3) Failure to set up playback to Bars 4) Screwing with menus and switches 63
Videotape Formats Legacy Analog: § VHS, S-VHS, Hi-8 § 3/4” (U-matic), 1” § Betacam, Beta SP 64
Videotape Formats Legacy Digital: § D-1, D-3 (component) § D-2 (composite) 65
Videotape Formats Digital Betacam Family: § Digi Beta § Betacam SX § Betacam IMX 66
Videotape Formats Other Current Digital: § D-5 § D-9 (Digital-S) 67
Videotape Formats DV-based: § DV, mini-DV § DVCam § DVCPro 25/50/100 68
PVW-2800 Internal View Control & Misc. Circuit Boards Threading Motor Video & Audio Circuit Boards Cassette Elevator Audio Heads Video Head Drum Capstan 69
VTR Systems § Video processing § Audio processing § Capstan servo -- controls tape movement § Drum servo -- controls head drum 70
VTR Servos § Lock to Reference input during playback § Lock to Record input during recording § Internal TBC (timebase corrector) may lock differently than servo system 71
VTR Tape Tracks Similar for analog or digital formats Longitudinal Audio Tracks Helical Video Tracks Longitudinal TC Track Longitudinal Control Track 72
VTR Recording Modes § E/E (electronics-to-electronics) -- passes input signals through to output § Hard (crash) Record -- erases and records all tracks at once, no sync with previous recording § Assemble Record -- erases and records all tracks, but picks up in sync with previous recording § Insert Record -- only erases and records selected tracks (control track must be present!) 73
VTR Front Panel Remote Select Timecode Display & Menus Audio Level Controls & Meters Editing Controls Timecode Controls may be various places! Transport Controls 74
VTR Rear Panel Connectors Analog Audio I/O Analog Video Inputs d Digital Audio I/O Digital Video I/O d d d Analog Video Ouputs d Remote Control And Misc. 75
Menus & Special Switches If your VTR has any of the following switches on the back… § Ref Auto/Manual: Set to AUTO § Audio input 600 -ohm terminations: Set to OFF § Audio input level: Set to HIGH 76
Menus & Special Switches When in doubt use the Factory Default settings! 77
Simple Troubleshooting Use good observation techniques: § Note all conditions during problem § Note conditions leading up to problem § When was the last good operation? What changed? § Be clear about meaning of words! 78
Troubleshooting Strategies § It pays to know how things are SUPPOSED to work. § Start with known good signals (bars and tone), good path and monitoring. § Change one thing and observe… § Swap things: cables, equipment, software § Cut problem in half 79
Troubleshooting Strategies Manuals are like GOLD! 80
Are you a professional? 81
Please send me feedback on this workshop! And visit the SMPTE booth on the exhibit floor! Eric Wenocur Lab Tech Systems Silver Spring, MD eric@lab-tech-systems. com Copyright 2006 Eric Wenocur All photos copyright their respective owners.
- Slides: 82