Clocking and Clocking and SynchronizationSynchronization

Clocking in the Digital StudioClocking in the Digital Studio

WordclockWordclock1. Digital audio is based upon sampling at regular 1. Digital audio is based upon sampling at regular intervalsintervals2. To keep the intervals constant requires a 2. To keep the intervals constant requires a consistent system clock consistent system clock 3. Wordclock is a signal of digital pulses which 3. Wordclock is a signal of digital pulses which provides a consistent timing reference and can be provides a consistent timing reference and can be routed to all digital devices in a setup- it does not routed to all digital devices in a setup- it does not contain any other data (like audio)contain any other data (like audio)

Clock Source for Digital DevicesClock Source for Digital Devices

Clock sourceClock source can be supplied internally via the unit can be supplied internally via the unit’’s s own oscillator or externally via wordclock, video (house own oscillator or externally via wordclock, video (house synch) or digital AES, SPDIF, etc. connectorssynch) or digital AES, SPDIF, etc. connectors

When making D to D copies, the receiving machine When making D to D copies, the receiving machine generally derive its clock reference from the incoming generally derive its clock reference from the incoming digital signal (AES, SPDIF, TDIF, etc.) or from the same digital signal (AES, SPDIF, TDIF, etc.) or from the same source that the sending machine is referenced to.source that the sending machine is referenced to.

Jitter - Time Based ErrorJitter - Time Based Error

Common Causes of JitterCommon Causes of Jitter It is caused by varying time delays in It is caused by varying time delays in

the circuit paths from component to the circuit paths from component to component in the signal path. component in the signal path.

The two most common causes of The two most common causes of jitter are poorly-designed Phase jitter are poorly-designed Phase Locked Loops (PLL's) and... Locked Loops (PLL's) and...

Waveform distortion due to Waveform distortion due to mismatched impedances and/or mismatched impedances and/or reflections in the signal path.reflections in the signal path.

JitterJitter In order to reduce jitter it is necessary to In order to reduce jitter it is necessary to

lock overall sample rate timing of all lock overall sample rate timing of all devices to a single consistent master devices to a single consistent master clockclock

Improper clocking will result in jitter and if Improper clocking will result in jitter and if severe enough - audible clicks and pops.severe enough - audible clicks and pops.

Low level jitter has no effect on D-D Low level jitter has no effect on D-D transferstransfers

Low level jitter can cause loss of low-Low level jitter can cause loss of low-level resolution on D/A converters, but itlevel resolution on D/A converters, but it ’’s s subtlesubtle

Jitter on A/D converters can introduce Jitter on A/D converters can introduce permanent distortion into the signalpermanent distortion into the signal

Word Clock Set Up In a Digital StudioWord Clock Set Up In a Digital Studio

Digital Synch Set Up using Optical ADAT Digital Synch Set Up using Optical ADAT connectionsconnections

Digital Audio Transfer Digital Audio Transfer ProtocolsProtocols

A. AES/EBUA. AES/EBU

B. S/PDIFB. S/PDIF

C. Optical (lightpipe)C. Optical (lightpipe)

D. MADID. MADI

E. T/DIFE. T/DIF

F. mLANF. mLAN

AES3 StandardAES3 Standard1. This standard, commonly known as AES/EBU, 1. This standard, commonly known as AES/EBU, was officially published in 1992 as a standard for was officially published in 1992 as a standard for carrying digital audio between different devicescarrying digital audio between different devices

2. Uses balanced, twisted pair 110 ohm cables 2. Uses balanced, twisted pair 110 ohm cables and XLR connectorsand XLR connectors

3. Each cable carries 2 channels of audio (one 3. Each cable carries 2 channels of audio (one direction only) and clock infodirection only) and clock info

S/PDIFS/PDIF1. Consumer version of the AES standard 1. Consumer version of the AES standard

2. Uses 75 ohm coaxial cable with RCA 2. Uses 75 ohm coaxial cable with RCA connectors (a more common and inexpensive connectors (a more common and inexpensive cable/ connector) orcable/ connector) or

3. TOSLINK optical cable 3. TOSLINK optical cable

4. Like AES each cable carries 2 channels of 4. Like AES each cable carries 2 channels of audio (one direction only) and clock infoaudio (one direction only) and clock info

5. SCMS - copy protection (SPDIF format only)5. SCMS - copy protection (SPDIF format only)

ADAT LightpipeADAT Lightpipe1. Introduced in 1991 with the ADAT MDM 1. Introduced in 1991 with the ADAT MDM

2. Uses a fiber optic cable2. Uses a fiber optic cable

3. Capable of carrying 8 channels of digital audio 3. Capable of carrying 8 channels of digital audio and clockand clock

4. Is now common on a variety of interfaces and 4. Is now common on a variety of interfaces and digital audio devicesdigital audio devices

MADIMADI1. Is an extension of the AES31. Is an extension of the AES3 format, and was format, and was defined as early as 1989defined as early as 1989

2. Uses a fiber optic or coaxial cable 2. Uses a fiber optic or coaxial cable

3. Capable of carrying 28, 56 or 64 channels of 24 3. Capable of carrying 28, 56 or 64 channels of 24 bit (up to 96kHz) audio over a single cablebit (up to 96kHz) audio over a single cable

4. Is now common on a variety of interfaces and 4. Is now common on a variety of interfaces and digital audio devicesdigital audio devices

5. Can carry numerous synch codes at various 5. Can carry numerous synch codes at various sample rate speeds (can vari speed up or down sample rate speeds (can vari speed up or down 12.5% at rates between 32 - 48 kHz)12.5% at rates between 32 - 48 kHz)

TDIF/TDIF 2TDIF/TDIF 21. Developed by the Tascam corporation for the 1. Developed by the Tascam corporation for the transfer of digital audio in their MDM line (DA-transfer of digital audio in their MDM line (DA-8888’’s) s)

2. Uses a shielded multi-conductor cable with a d-2. Uses a shielded multi-conductor cable with a d-sub 25 pin connector sub 25 pin connector

3. Capable of carrying 8 channels of digital audio 3. Capable of carrying 8 channels of digital audio over a single cable (bi directional)over a single cable (bi directional)

4. Is now common on a variety of interfaces and 4. Is now common on a variety of interfaces and digital audio devices for transferring multi-channel digital audio devices for transferring multi-channel digital audio.digital audio.

5. TDIF 2 can carry synch, TDIF 1 cannot5. TDIF 2 can carry synch, TDIF 1 cannot

mLANmLAN1. Developed by Yamaha corporation - mLAN allows for the 1. Developed by Yamaha corporation - mLAN allows for the transfer of multi channel digital audio and MIDI data over a transfer of multi channel digital audio and MIDI data over a single 1394 FireWire or iLINK cablesingle 1394 FireWire or iLINK cable

2. Theoretically supports approx. 100 channels of digital 2. Theoretically supports approx. 100 channels of digital audio and up to 256 ports of MIDI data between digital audio and up to 256 ports of MIDI data between digital audio devices at speeds up to 400 Mbps (bi directional)audio devices at speeds up to 400 Mbps (bi directional)

3. Can transmit and resolve word clock issues allowing 3. Can transmit and resolve word clock issues allowing devices to run at different sample rates on the same devices to run at different sample rates on the same networknetwork

4. Utilizing the patch bay application included with mLAN 4. Utilizing the patch bay application included with mLAN products, devices can be routed and configured within the products, devices can be routed and configured within the softwaresoftware

5. This format can run with or without a computer5. This format can run with or without a computer

5. Over 140 companies have signed on as mLAN licensees5. Over 140 companies have signed on as mLAN licensees

Synchronization was developed to allow multiple Synchronization was developed to allow multiple visual and audio media to maintain a direct time visual and audio media to maintain a direct time

relationship (the occurrence of two or more relationship (the occurrence of two or more events at precisely the same time).events at precisely the same time).

SynchronizationSynchronization

Synchronization has two concepts that need to Synchronization has two concepts that need to be independently addressedbe independently addressed

Where are we? (positional reference)Where are we? (positional reference)

How fast are we going? (clock reference)How fast are we going? (clock reference)

Positional Reference is Positional Reference is Known as SMPTE Time CodeKnown as SMPTE Time Code

SMPTE - Society of Motion Picture and Television SMPTE - Society of Motion Picture and Television EngineersEngineers

SMPTE time code was invented so that the locations of SMPTE time code was invented so that the locations of analog linear audio and video tapes could be specified analog linear audio and video tapes could be specified with a high degree of accuracy.with a high degree of accuracy.

By recording SMPTE code on a track of the audio or By recording SMPTE code on a track of the audio or video tape, we have a way of identifying specific sections video tape, we have a way of identifying specific sections of tape on multiple machines, and with a master of tape on multiple machines, and with a master synchronizer, controlling the speed of each machine so synchronizer, controlling the speed of each machine so that they all run togetherthat they all run together

The SMPTE addressThe SMPTE address

Even though it is audible when played back from a Even though it is audible when played back from a longitudinal audio or video track, SMPTE is NOT an longitudinal audio or video track, SMPTE is NOT an

analog audio signal. Rather, it is an analog analog audio signal. Rather, it is an analog representation of a DIGITAL signalrepresentation of a DIGITAL signal

The time code addressThe time code address

Hours - 24 hr clockHours - 24 hr clock MinutesMinutes SecondsSeconds FramesFrames Frame rates (per second) include 24, 25, Frame rates (per second) include 24, 25,

29.97, and 3029.97, and 30

SMPTE Frame RatesSMPTE Frame Rates

30 FPS: Original format developed for black&white video 30 FPS: Original format developed for black&white video - commonly used for audio only applications- commonly used for audio only applications

30 Drop Frame: Used for audio recordings for film-30 Drop Frame: Used for audio recordings for film-originated programs that are destined for NTSC (color) originated programs that are destined for NTSC (color) broadcastbroadcast

29.97 Non Drop Frame: NTSC color video frame rate29.97 Non Drop Frame: NTSC color video frame rate 29.97 Drop frame: Utilized by broadcasters because 1 29.97 Drop frame: Utilized by broadcasters because 1

hour of drop frame TC will equal 1 hour of actual hour of drop frame TC will equal 1 hour of actual elapsed time. Runs at same speed as above but drops 2 elapsed time. Runs at same speed as above but drops 2 frames at the top of each minute with the exception of frames at the top of each minute with the exception of every 10th minute.every 10th minute.

More SMPTE Frame RatesMore SMPTE Frame Rates

25 FPS: Also called EBU (European Broadcast Union) 25 FPS: Also called EBU (European Broadcast Union) format. Utilized by broadcasters throughout Europeformat. Utilized by broadcasters throughout Europe

24 FPS: This format is used for film applications. Film is 24 FPS: This format is used for film applications. Film is typically photographed and projected at 24 FPS, so this typically photographed and projected at 24 FPS, so this format is useful when 1 TC frame should equal one film format is useful when 1 TC frame should equal one film frameframe

LTC and VITCLTC and VITCLTC = Longitudinal Time CodeLTC = Longitudinal Time Code

VITC = Vertical Interval Time CodeVITC = Vertical Interval Time Code LTC is recorded onto one track of a multi track LTC is recorded onto one track of a multi track

audio tape, or on a video cue track. LTC can be audio tape, or on a video cue track. LTC can be added to audio tape AFTER recording. LTCadded to audio tape AFTER recording. LTC cannot cannot be read at very slow speeds or when be read at very slow speeds or when stopped.stopped.

VITC is recorded onto video tape as part of the VITC is recorded onto video tape as part of the video signal, and CANNOT be added after the video signal, and CANNOT be added after the video signal has been recorded. VITC video signal has been recorded. VITC cancan be be read at very slow speeds or when stopped.read at very slow speeds or when stopped.

Challenges of synching tape Challenges of synching tape machinesmachines

AC Voltage fluctuations – affects the speed of AC Voltage fluctuations – affects the speed of the capstan motorthe capstan motor

Tape slippageTape slippage Design differencesDesign differences ConditionCondition

All of these factors contribute to the lack of All of these factors contribute to the lack of constant speedconstant speed

A stable clock reference corrects thisA stable clock reference corrects this

Stable Clock sources for ATR/ VTR Stable Clock sources for ATR/ VTR MachinesMachines

Synchronizer’s internal clock: clock reference derived Synchronizer’s internal clock: clock reference derived from internal crystal oscillator in synchronizer unit.from internal crystal oscillator in synchronizer unit.

Black Burst Generator: Also called house sync or video Black Burst Generator: Also called house sync or video ref, produces a very stable timing reference to resolve ref, produces a very stable timing reference to resolve speeds of multiple video decks. Preferred method for speeds of multiple video decks. Preferred method for synching multiple ATR’s and digital systems too.synching multiple ATR’s and digital systems too.

Running Wild: ATR or video deck runs on its own Running Wild: ATR or video deck runs on its own internal crystal oscillator - not resolved to an outside internal crystal oscillator - not resolved to an outside clock source – not preferable when synching with clock source – not preferable when synching with SMPTE.SMPTE.

The SynchronizerThe Synchronizer

A Synchronizer provides the A Synchronizer provides the following functions:following functions:

LTC/VITC SMPTE Generator: used to LTC/VITC SMPTE Generator: used to stripe tapes with time codestripe tapes with time code

Resolves the speeds of tape decks to a Resolves the speeds of tape decks to a common source – either it’s own internal common source – either it’s own internal oscillator or an external source such as oscillator or an external source such as Black Burst.Black Burst.

Clock reference with respect to analog audio Clock reference with respect to analog audio and video systems, is achieved by resolving and video systems, is achieved by resolving

the transport speeds of two or more machines the transport speeds of two or more machines to a common clock sourceto a common clock source

Black Burst GeneratorsBlack Burst Generators

Uses a 75 ohm, video cable with a BNC connector Uses a 75 ohm, video cable with a BNC connector (same as word clock).(same as word clock).

Is a blank video signal (video signal with no picture data) Is a blank video signal (video signal with no picture data) which serves as a stable timing reference.which serves as a stable timing reference.

Most VTR’s, DAW synch peripherals, synchronizers and Most VTR’s, DAW synch peripherals, synchronizers and DTR’s are able to reference Black Burst making it a DTR’s are able to reference Black Burst making it a common clock source in studios.common clock source in studios.

Black Burst GeneratorsBlack Burst Generators

Studio Synch Set Up with Tape Studio Synch Set Up with Tape MachinesMachines

Studio Synch Set Up with Studio Synch Set Up with Tape Machines and a DAWTape Machines and a DAW

Types of Clock Sources

Applications Types of SMPTE Applications

Word Clock – uses 75 ohm video cable w/ BNC connections

Linear/non-linear digital recorders and digital signal processors

LTC – carried via balanced audio cable (XLR or TRS connections)

Analog tracks of ATRs and VTRs, DTRs and DAW synch peripherals

Video Ref (Black Burst) – uses 75 ohm video cable w/ BNC connections

VTRs, DTRs, Synchronizers, DAW synch peripherals (Synch HD)

VITC – uses 75 ohm video cable w/ BNC connections

VTRs, DTRs and DAW synch peripherals

Synchronizer’s internal oscillator – uses a multi-pin control cable.

ATRs, VTRs(note: some synchronizers are able to supply word clock)

MTC – uses standard 5-pin (DIN) MIDI cable

MIDI sequencers, DAW synch peripherals

Bi Phase/Pilot Tone – uses a multi-pin control cable.

ATRs, Cameras, (Archaic – currently not in use)