Alesis ADAT-XT Digital Recording Concepts, Analog Recording Basics, Digital Recording Basics

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Digital Recording Concepts: Appendix A

APPENDIX A

DIGITAL RECORDING CONCEPTS

ANALOG RECORDING BASICS

Digital recording works very differently from analog recording. With analog recording, tape containing millions of tiny magnetizable particles move past a record head. The magnetic field around this head fluctuates according to the audio signal present at the tape recorder’s input. These fluctuations permanently rearrange the particles on the tape to form a pattern that is analogous to the original audio signal.

On playback, the patterns on tape are read by a separate playback head (or from the record head, set up to read instead of record signals) that converts the magnetic fluctuations back into an audio signal.

The biggest problem with analog recording is that the tape itself alters the sound originally recorded on tape. Tape hiss is one problem; it superimposes a low-level rushing noise onto the audio signal. Although there are ways to minimize noise, such as noise reduction circuitry, this colors the sound in the process of masking the noise. Tape’s frequency response is also an issue. Tape has a hard time “absorbing” higher frequencies, which can dullen the sound. Moving tape faster allows the heads to magnetize more particles and extends the high frequency response, but the tradeoff is increased tape costs, and heftier transports to move bigger reels of tape.

DIGITAL RECORDING BASICS

With digital recording, the technology is very similar — tape moves past a record head, and plays back through a playback head. However, the signal recorded on tape is very different.

Audio signals entering each channel of the XT first pass through an analog-to-digital (A/D) converter, a device that takes 48,000 samples or “snapshots” of the signal level every second 1. Each sample is assigned a specific numeric value that corresponds to its level.

Analog Signal

Digital Signal

A/D

These numbers, which represent coded audio, are then converted into an audio signal that can be recorded on tape. Fortunately, recording a number on tape doesn’t degrade the signal.

During playback, a digital-to-analog (D/A) converter reads the numbers from tape and outputs a corresponding level. This creates a “stairstep” reconstruction of the original signal, which is close to (but not exactly) the same as the original signal. To complete the process, this stairstep signal is smoothed by a low pass filter. The result is natural-sounding audio that sounds virtually unchanged from what was originally recorded.

148,000 samples are taken per second at a sampling rate of 48 kHz; 44,100 samples are taken per second at a sampling rate of 44.1 kHz.

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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 AC Power Hookup Setting UPUnpacking and Inspection ChapterSetting Up Line Conditioners and Protectors About Audio CablesInput Normaling Basic Audio HookupWord on ADAT’S S-VHS Cassette Tape Threaded VS. UnthreadedThermal Considerations in Rack Mounting Operating EnvironmentMounting on a Shelf or NON-RACK Enclosure Avoiding Electromagnetic InterferenceYour First Session POWER-UP,AND Tape InsertionABS 0H 15M 48S ABS n0 F0Sample Rate Selection Formatting a Tape a MustFormatting a NEW Tape Recording While FormattingTo record-enable a track Track Selection and Setting LevelsREL 0H 01M 29S Making a RecordingRecording Transport ButtonsTo make a recording Record LED turns off, while the Play LED remains litTo engage Cue mode To engage Review modePlayback Reviewing and CueingLocating REL 0H 00M 00SPage To loop a section of tape Creating a LoopRehearsing Automated RecordingTo automatically punch in and out Measure twice or more, and cut only onceABS 00 % 00 C Track Delay70 mS Pitch ControlTrack Copy To adjust the display brightnessDisplay Brightness To bounce audio from one track to anotherConnections Input Jack CharacteristicsAnalog Audio Unbalanced Inputs Analog Audio Unbalanced OutputsAdditional grounds Analog Audio Balanced Inputs and OutputsInput Mode Analog Audio Input ModeTo synchronize multiple XTs and/or ADATs Sync IN/OUTTo connect the digital optical network Digital Audio IN/OUTRehearse and Auto Record features FootswitchesXT Remote VersaTape Formatting Basic OperationsFormatting Considerations Complete FormatBe sure the tape is completely rewound Format ExtendABS Pr 0t 0 n ABS Pr 0t 0 FFWrite Protect Override To extend the format on a partially formatted tapeReading the Display Display Icons Basic Operations Time Counter & ABS/REL Button 01M 29SLocate SelectedEdit Value Button Basic EditingEntering Numeric Values Editing Individual DigitsAnalog Input Input SelectDigital Input Track CopyBasic Operations ALL Input Monitor Input MonitorAuto Input Monitor Fine Meter Mode Peak Mode ButtonMeters Recording a Benchmark T APESetting Levels Record EnableEject Transport ControlsRewind /REVIEW Fast Forward /CUEStop RECORD/PUNCH in or OUTWhether the tape being played is formatted or not To start recordingRecord Crossfade Time Sample Rate ClockPositions as before To select the sample rateTo set the Crossfade Time FA dE 2Displaying Frames VS THS/SECONDS About Pitch Changing To set the Track Delay amount To turn Track Delay on and offTo set multiple tracks to the same Track Delay value 10 mSLocate Autolocation ControlsAbsolute ABS Time VS . Relative Time Locating Setting Locate PointsTo store a Locate Point memory on the fly To edit a Locate Point memoryAuto Return Auto LoopingAuto Play Loop LimitTape Length Auto RecordLooped 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 Achieving Lock Master /SLAVE InteractionMaster Format ENABLED, Complete Format Independent Slave ModeMaster Format ENABLED, Format Extend Formatting Multiple TapesBefore punching into format record Master Format DisabledMaster Format DISABLED, Format Extend Recording Digital Audio Making Digital BackupsBouncing Tracks Between Adats Reassigning Channels to Different TracksRecording Digital Audio from Other Sources To make a backup tapeDigital Clock Considerations Tape OffsetABS 0H 00M 00S Setting the Machine OffsetXT Transport Speed Combining XTS and AdatsSample 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 Combined MULTITRACK/MASTERING Deck ApplicationsLIVE/LONG-TERM Recording Locking to Video Code only Master Midi Machine Control Virtual Remote ControlComputer Control Midi Systems Virtual TrackingModular Recording Libraries and ArchivesCalculating Tape Offset Using the Locates Using Track Copy AS a Digital RouterPress Edit VALUE, then press Locate Analog Recording Basics Digital Recording ConceptsDigital Recording Basics Appendix aWHY S-VHS? TROUBLE-SHOOTING Index TroubleshootingRE-INITIALIZING Appendix BAbout Error Rate Readings Error Rate DisplayABS d1 SP E rr ABS d1 SP r E9Adat Head Maintenance MAINTENANCE/SERVICE Tape Maintenance Safe TapeCleaning Drum Time DisplayObtaining Repair Service MaintenanceRefer ALL Servicing to Alesis Customers in the USAAppendix B Troubleshooting Appendix C Error CodesAutomatic Brake Calibration Procedure Appendix D SpecificationsSteps to Take Before Calling for Help Audio Digital Inputs/Outputs Or Analog-to-Digital Converter GlossaryDAT BusMMC MidiSMPTE/LTC OutputVitc VHSIndex Index Adat XT Reference Manual
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