Alesis ADAT-XT manual Polarity Differences, Connections, Here are some possible solutions

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Chapter 5: Multiple ADAT-XT Operation

POLARITY DIFFERENCES

The original ADAT was designed to invert its analog input signal internally before the audio was sent through the A/D (analog-to-digital) converter and recorded onto tape. The digital representation of the data (as stored on tape) was therefore inverted relative to the analog input (i.e., a positive voltage at the analog input is stored as a negative number on the tape). When this digital signal was played back from tape, the data was sent to a D/A (digital-to-analog) converter, and the analog signal output of the D/A was inverted once again before going to the output jacks. This resulted in the input to output phase being correct, and no phase problems were experienced when using a single ADAT or a multiple ADAT system.

However, neither the digital input nor the digital output was inverted. Therefore, if one transfers the ADAT’s digital audio data to a DAT machine or hard disk recording system (using the AI-1 or a similar digital interface), the audio output from the other device would likely be out of phase with the ADAT, since it probably does not invert the analog signal after its D/A converters. Although this in and of itself will not usually be a problem, it may cause some confusion if multiple correlated audio signals are combined from multiple sources since there is a possibility that signals could become out of phase.

To prevent this from occurring, the XT design has been improved so that the polarity remains constant from the analog to digital, and back to analog, domain. Like the original ADAT, the result from one machine, or multiples of the same machine, is the same: The input to output phase is correct. However, if two cloned tapes (copied digitally either with ADATs, ADAT XTs, or both) are played back in sync on both an ADAT and an XT, the outputs of the two machines will be out of phase relative to each other. Since it does not usually serve any practical purpose to play the same signal from two different tapes with two different model machines simultaneously, this should not present a problem for you. This design improvement is only mentioned here to explain this possible situation should you happen to experience it.

Possible problem: Let’s say you had been using a multiple ADAT system and you recorded a stereo signal across two machines (a stereo drum recording on tracks 8 and 9), where there is a common element to each track (i.e. center signal). If you replace one of these machines with an XT, the result would be that the track being played back on the XT will be out of phase from the track played on the ADAT, canceling the center signal.

Here are some possible solutions:

•Use a phase switch on your mixer (if your mixing board provides this) to invert the phase of the problem track to compensate.

•Wire your patchbay or ELCO cable to reverse the input and output polarity of the XTs in the system, but use standard cables on the ADATs in the system. This is recommended only for studios where master tapes will be exchanged between units or sent out of house.

•Digitally bounce one of the stereo tracks to the other ADAT so that both sides play back from the same machine.

•Most importantly, it is better to plan recording sessions so that stereo tracks reside on the same physical tape in a multiple ADAT system.

CONNECTIONS

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ADAT XT Reference Manual

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Contents Alesis ADAT-XT Introduction Adat XT Reference Manual Conventions Adat XT Reference Manual Contents Basic Operations Analog Recording Basics Digital Recording Basics Why S-VHS? Index Maintenance/Service Cleaning Obtaining Repair Service Setting UP AC Power HookupUnpacking and Inspection ChapterSetting Up About Audio Cables Line Conditioners and ProtectorsBasic Audio Hookup Input NormalingThreaded VS. Unthreaded Word on ADAT’S S-VHS Cassette TapeOperating Environment Thermal Considerations in Rack MountingMounting on a Shelf or NON-RACK Enclosure Avoiding Electromagnetic InterferencePOWER-UP,AND Tape Insertion Your First SessionABS 0H 15M 48S ABS n0 F0Formatting a Tape a Must Sample Rate SelectionFormatting a NEW Tape Recording While FormattingTrack Selection and Setting Levels To record-enable a trackREL 0H 01M 29S Making a RecordingTransport Buttons RecordingTo make a recording Record LED turns off, while the Play LED remains litTo engage Review mode To engage Cue modePlayback Reviewing and CueingREL 0H 00M 00S LocatingPage Creating a Loop To loop a section of tapeAutomated Recording RehearsingTo automatically punch in and out Measure twice or more, and cut only onceTrack Delay ABS 00 % 00 C70 mS Pitch ControlTo adjust the display brightness Track CopyDisplay Brightness To bounce audio from one track to anotherInput Jack Characteristics ConnectionsAnalog Audio Unbalanced Inputs Analog Audio Unbalanced OutputsAnalog Audio Balanced Inputs and Outputs Additional groundsAnalog Audio Input Mode Input ModeSync IN/OUT To synchronize multiple XTs and/or ADATsDigital Audio IN/OUT To connect the digital optical networkFootswitches Rehearse and Auto Record featuresXT Remote VersaBasic Operations Tape FormattingFormatting Considerations Complete FormatFormat Extend Be sure the tape is completely rewoundABS Pr 0t 0 FF ABS Pr 0t 0 nWrite Protect Override To extend the format on a partially formatted tapeReading the Display Display Icons Basic Operations 01M 29S Time Counter & ABS/REL ButtonLocate SelectedBasic Editing Edit Value ButtonEntering Numeric Values Editing Individual DigitsInput Select Analog InputDigital Input Track CopyBasic Operations ALL Input Monitor Input MonitorAuto Input Monitor Peak Mode Button Fine Meter ModeMeters Recording a Benchmark T APERecord Enable Setting LevelsTransport Controls EjectRewind /REVIEW Fast Forward /CUERECORD/PUNCH in or OUT StopWhether the tape being played is formatted or not To start recordingSample Rate Clock Record Crossfade TimePositions as before To select the sample rateTo set the Crossfade Time FA dE 2Displaying Frames VS THS/SECONDS About Pitch Changing To turn Track Delay on and off To set the Track Delay amountTo set multiple tracks to the same Track Delay value 10 mSLocate Autolocation ControlsAbsolute ABS Time VS . Relative Time Setting Locate Points LocatingTo store a Locate Point memory on the fly To edit a Locate Point memoryAuto Looping Auto ReturnAuto Play Loop LimitAuto Record Tape LengthLooped Recording RehearsalErroneously selected, to avoid damage to the tape To set the tape lengthEuropean equivalents and approximate recording times Footswitch Controlled Autolocating Footswitch ControlsFootswitch Controlled Punching Using the XT Remote Synchronizing Machines OperationOverview Master /SLAVE Interaction Achieving LockIndependent Slave Mode Master Format ENABLED, Complete FormatMaster Format ENABLED, Format Extend Formatting Multiple TapesBefore punching into format record Master Format DisabledMaster Format DISABLED, Format Extend Making Digital Backups Recording Digital AudioBouncing Tracks Between Adats Reassigning Channels to Different TracksTo make a backup tape Recording Digital Audio from Other Sources Tape Offset Digital Clock ConsiderationsSetting the Machine Offset ABS 0H 00M 00SCombining XTS and Adats XT Transport SpeedSample Rate VS. Pitch Control Input MonitoringConnections Here are some possible solutionsPolarity Differences Multiple ADAT-XT Operation Chapter Multiple ADAT-XT Operation Adat XT Reference Manual Applications Combined MULTITRACK/MASTERING DeckLIVE/LONG-TERM Recording Midi Machine Control Virtual Remote Control Locking to Video Code only MasterComputer Control Midi Systems Virtual TrackingLibraries and Archives Modular RecordingUsing Track Copy AS a Digital Router Calculating Tape Offset Using the LocatesPress Edit VALUE, then press Locate Digital Recording Concepts Analog Recording BasicsDigital Recording Basics Appendix aWHY S-VHS? Troubleshooting TROUBLE-SHOOTING IndexRE-INITIALIZING Appendix BError Rate Display About Error Rate ReadingsABS d1 SP E rr ABS d1 SP r E9Adat Head Maintenance Tape Maintenance Safe Tape MAINTENANCE/SERVICECleaning Drum Time DisplayMaintenance Obtaining Repair ServiceRefer ALL Servicing to Alesis Customers in the USAAppendix B Troubleshooting Error Codes Appendix CAutomatic Brake Calibration Procedure Appendix D SpecificationsSteps to Take Before Calling for Help Audio Digital Inputs/Outputs Glossary Or Analog-to-Digital ConverterBus DATMidi MMCOutput SMPTE/LTCVHS VitcIndex Index Adat XT Reference Manual
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