dolby® digital / ac-3 encoding using the argus ... - TBC Integration

DOLBY ® DIGITAL / AC-3ENCODING USING THEARGUS ® ENCODERDocument Part Number 9050-0520

Contents (Con’t)Bandwidth Low-pass Filter ............................................................................ 11LFE Low-pass Filter ...................................................................................... 1290-Degree Phase Shift .................................................................................. 123 dB Attenuation ............................................................................................ 12Figure 3. Preprocessing Property Page ................................................................ 12Compression Characteristic.......................................................................... 13RF Overmodulation Protection ..................................................................... 13Input/Output Property Page ..................................................................... 13Input Channel Assignments .......................................................................... 13Figure 4. Input/Output Property Page .................................................................... 13Output Mode .................................................................................................. 14Stream Number ............................................................................................. 14Time Codes ................................................................................................... 14Audio Output .................................................................................................. 14File Format .................................................................................................... 14Playback Clock Source ................................................................................. 14Block Diagram ........................................................................................... 14Typical Installation .................................................................................... 14Figure 5. AC-3 Encoder Block Diagram ................................................................. 15Figure 6. Typical Installation Layout ....................................................................... 15Copyright 2002, Vela LPRev. 0, Feb 2002

Dolby Digital / AC-3Encoding Using theArgus EncoderIntroductionThe ability to encode an Dolby ® Digital/AC-3 stream in addition to thestandard MPEG audio and video streams is an optional feature availablewith Vela’s Argus ® software release 2.6.1 and later.The Momentum-designed “Opus” encoder board, which the Argus usesfor Dolby Digital/AC-3 encoding, is a 24-bit multi-channel digital audioprocessor for the PCI bus. Among its features are the following:• Four stereo digital (AES) inputs• One stereo digital audio output• SMPTE time code input• 80 MHz, 24-bit digital signal processors (DSPs)• High-speed PCI bus• Standard Dolby Digital 5.1 encode program• AES/EBU or S/PDIF digital audio I/O formats• RS-422 interface• Included audio input/output cableA comprehensive software application accompanies the encoder boardto complete the Dolby Digital/AC-3 encoding solution for the Argus.A block diagram of the system can be found in Figure 5. A drawing thatshows the Momentum board in a typical Argus encoder configuration iscan be found in Figure 6.Getting StartedIn order to maximize your use of the Dolby Digital/AC-3 encodingsolution for the Argus, you must first:• Install the Momentum encoder board in an unused PCI slot.Argus is a registered trademark of Vela LP. Dolby is a trademark of Dolby Laboratories.All other trademarks, brand names, or product names appearing in this publication areregistered to the respective companies or organizations that own the names or trademarks.

6Dolby Digital / AC-3 Encoding Using the Argus Encoder• Connect the supplied input/output cable to the board’s D-connector.• Install the software for the Momentum Dolby Digital/AC-3encoder, making sure that the Momentum microcode is located inthe directory from which the FMTestApp (or EDL Editor) applicationis run. The Momentum microcode is comprised of three files:enc13.cld, enc23.cld, and enc33.cld.• Before starting the application, make certain that the registry keyHKEY_CURRENT_USER\Software\Vela Research\BroadcastArgus\EncoderConfig\AC3Installed is set to 1.• Before cueing for an encode, use the Dolby ® Parameter ControlApplication to activate Dolby Digital/AC-3 encoding and to set allof the Dolby-related parameters.Dolby Parameter Control ApplicationMost of the parameters related to Dolby Digital/AC-3 encoding can beset using the Dolby Parameter Control Application. The one notable exceptionto this rule is the setting of the PID when the Dolby Digital/AC-3 stream is to be included in a transport stream. The Dolby PID is setusing the Mux property page of RegCtrlPnl.The Dolby Parameter Control Application has four property pages:Configuration Control, Bitstream Info, Preprocessing, and Input/Output.Configuration Control Property PageIt is from the Configuration Control property page (Figure 1) that youturn Dolby Digital/AC-3 encoding on or off and that you set the bit rateand sample rate of the AC-3 stream. The following properties are representedon the Configuration Control page:Dolby EnabledCheck this checkbox if and only if you wish to include a Dolby Digital/AC-3 stream in the next encoded file.Time Code StartCheck this checkbox if and only if you wish to use the mark-in and mark-outof the VTR component to control the start and stop of the next Dolby Digital/AC-3 encode. Several requirements must be met in order to use this option:1. VTR control must be enabled. Use the VTR Control page on the EDLEditor or the VTR property page on RegCtrlPnl to enable VTR control.

Dolby Digital / AC-3 Encoding Using the Argus Encoder 7Figure 1. Configuration Control Property Page2. The Momentum board must be supplied with a time-code input signal.For example, the time-code-out of the tape deck might be connectedto the time-code-in cable supplied with the Momentum encoder.3. The mark-in and mark-out supplied through the EDL Editor or throughRegCtrlPnl must be valid time codes that will be provided to theMomentum encoder by the time-code generator.4. Prior to the encode, the tape must be pre-rolled to a point well ahead ofthe mark-in.Start DelayThe numeric value in this field specifies the number of milliseconds thatthe Argus encoder will wait after starting the Momentum encoder beforestarting the IBM audio and video encoders. The default value is 75 msec.A negative value may be provided. If the value is negative, the IBM audioand video encoders will be started before the Momentumencoder is started. This value can be adjusted to guarantee propersynchronization of the video and Dolby Digital/AC-3 content.Data RateThis field specifies the speed in kilobits per second at which the Dolby

Dolby Digital / AC-3 Encoding Using the Argus Encoder 9Dialog NormalizationThis parameter allows for uniform reproduction of spoken dialog whendecoding any AC-3 bit stream. Its value indicates how far the subjectivedialog level of the encoded program falls below digital 100% full scale(0 dBFS). The setting (between -1 and -31 dB) is not used directly by theDolby Digital/AC-3 decoder, but is used by a section of the sound reproductionsystem to set the audio reproduction volume.Dialog Normalization Channel 2This parameter serves the same purpose as the Dialog Normalizationsetting, described above; however, it applies to the second channel of adual-mono bit. It is ignored if the audio coding mode is not 1+1.Enable Low-Frequency EffectsThis setting enables or disables the optional low-frequency effects channel.This LFE channel of limited bandwidth (

10Dolby Digital / AC-3 Encoding Using the Argus EncoderFigure 2. Bitstream Info Property PageDolby Surround ModeThis setting specifies whether or not a two-channel Dolby digital bit streamis conveying a Dolby Surround encoded program. This parameterappears in the bit stream only when the audio coding mode is set to 2/0.Copyright BitThe setting of this checkbox indicates whether or not the included audiocontent is protected by copyright.Original Bit StreamThe setting of this checkbox specifies whether the AC-3 content is anoriginal bit stream (checked) or just a copy of the original (unchecked).Info ExistsThis setting specifies whether or not audio production information(mixing level and room type) exist within the AC-3 bit stream.Mix LevelActive only when the Info Exists checkbox is checked, this setting indicatesthe absolute acoustic Sound Pressure Level (SPL) of an individualchannel (usually the center channel dialog level) during the final audio

Dolby Digital / AC-3 Encoding Using the Argus Encoder 11mixing session. The peak mixing level, ranging from 80 to 111 dB SPL,is the acoustic level of a sine wave in a single channel whose peak reachesdigital 100% full scale (0 dBFS) in the PCM representation. The absoluteSPL is typically measured using pink noise at -20 or -30 dB RMS withrespect to the peak RMS sine wave level. The Mix Level value is notnormally used within the Dolby Digital decoder, but may be used byother elements in an audio system. This setting appears in the streamonly when the Info Exists checkbox is checked.Room TypeThis setting indicates the type and calibration of the room used for the finalaudio mixing session. It is not normally used within the Dolby Digitaldecoder, but may be used by other elements in an audio system. This settingappears in the stream only when the Info Exists checkbox is checked.Channel 2 Info Exists, Channel 2 Mix Level, Channel 2 Room TypeThese settings all apply to the second channel in a dual-mono bit streamwhen the audio coding mode is set to 1+1. They are ignored if the audiocoding mode is not 1+1. Please refer to the descriptions of Info Exists,Mix Level, and Room Type, above, for a complete description of each ofthese parameters.Preprocessing Property PageThe settings on the Preprocessing property page (Figure 3) control themanner in which the incoming PCM data is processed before being sentto the encoding algorithm.Digital De-emphasisWhen an incoming PCM signal has been digitally emphasized, it isusually advisable to de-emphasize that signal before encoding it. If youcheck the Auto checkbox, the AC-3 encoder will decide, based on theincoming audio, whether or not to apply de-emphasis.DC High-pass FilterThis checkbox either enables (checked) or disables a DC filter for allinput channels.Bandwidth Low-pass FilterThis checkbox either enables (checked) or disables a low-pass filter forall input channels.

12Dolby Digital / AC-3 Encoding Using the Argus EncoderFigure 3. Preprocessing Property PageLFE Low-pass FilterThis setting is used to activate a 120 Hz low-pass filter applied to the LFEinput channel. If the digital signal fed to the LFE input does not containinformation above 120 Hz, you may disable this filter.90-Degree Phase ShiftThis feature is used to generate multichannel AC-3 bit streams that maybe down-mixed in an external two-channel decoder to create an outputthat is truly compatible with Dolby Surround.3 dB AttenuationThis setting applies a 3 dB cut to the Surround channels of a multichannelfilm sound track when it is being transferred onto a formatfor consumer home theater playback. This feature is available becausecinema sound track Surround channels are mixed 3 dB “hot” relativeto the front channels in order to account for cinema amplifier gains.Home theater Surround gains are calibrated differently, thusrequiring a -3 dB adjustment to the Surround tracks.

Dolby Digital / AC-3 Encoding Using the Argus Encoder 13Compression CharacteristicThis setting specifies the characteristic curve of the Dynamic RangeCompression algorithm. If the compression characteristic setting is enabledduring the encode, a Dolby decoder will refer to this setting to reduce theaudio program's dynamic range. Available selections for this parameterinclude Film Standard, Film Light, Music Standard, Music Light, and Speech.RF Overmodulation ProtectionThis setting determines whether or not a RF preemphasis filter is used toprevent RF over-modulation in set-top-box decoders.Input/Output Property PageThe Input/Output property page allows you to control parameters directlyrelated to the incoming and outgoing digital signals. See Figure 4.Input Channel AssignmentsThe six controls in the left-most column (labeled “Input Channel Assignments”)allow you to associate each of the six input channels with a specificchannel of the source audio (left, right, center, left Surround, right Surround,and LFE). If the audio coding mode does not identify the channel as an activeinput, then the channel assignment is ignored.Figure 4. Input/Output Property Page

14Dolby Digital / AC-3 Encoding Using the Argus EncoderOutput ModeThe data signal sent by the encoder has an information field specifyingwhat format the data is in. The options are: (1) Consumer-Professional32-bit, (2) Professional 16-bit channel 1, and (3) Professional 16-bitchannel 2. A Dolby Digital/AC-3 decoder will use this value in a vendorspecificmanner.Stream NumberThis setting specifies the data stream number to be inserted into thepreamble of the IEC958 AC-3 output data. The valid range for thisparameter is 0 through 7, with a default value of 0.Time CodesThis settings specifies whether or not SMPTE time code packets are to beincluded in the encoder output.Audio OutputThis parameter determines the value of bit 1 (the audio/non-audio bit) ofthe channel status information contained in the IEC958 output. Annex Bof ATSC A/52 recommends setting this bit to 1 (non-audio data) inprofessional mode to indicate the presence of AC-3 data within the IEC958 interface. The bit must be set to 1 in the consumer mode.File FormatThis parameter is used in determining the format of recorded disk files.Playback Clock SourceThis parameter determines the source of the master audio clock duringplayback from a disk file. When this parameter is set to Internal Synchronization(0), the encoder will use one of the on-board oscillators,matching the detected sampling frequency of the disk file. When the clocksource parameter is set to External Synchronization (1), the encoder usesthe recovered clock from the digital input signal.Block DiagramThe illustration in Figure 5 shows system flow within the Dolby Digital/AC-3 encoder, the system PCI bus, and the Vela Argus encoder.Typical InstallationFigure 6 shows the Momentum “Opus” Dolby Digital/AC-3 encoder boardas typically installed in a Vela Argus rack-mount encoder system.

Dolby Digital / AC-3 Encoding Using the Argus Encoder 15Figure 5. AC-3 Encoder Block DiagramFigure 6. Typical Installation Layout

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