vela momentum user manual

8/2/2019 Vela Momentum User Manual

1/16

Document Part Number 9050-0520

DOLBYDIGITAL / AC-3ENCODING USING THE

ARGUS

ENCODER


2/16


3/16

Contents

Introduction .................................................................................... 5

Getting Started ............................................................................................ 5

Dolby Parameter Control Application ........................................... 6

Configuration Control Property Page ....................................................... 6

Dolby Enabled ................................................................................................. 6Time Code Start .............................................................................................. 6

Start Delay ....................................................................................................... 7

Data Rate ........................................................................................................ 7

Figure 1. Configuration Control Property Page ....................................................... 7

Sample Rate .................................................................................................... 8

Audio Coding Mode ......................................................................................... 8

Audio Bandwidth .............................................................................................. 8

Bit Stream Mode.............................................................................................. 8

Coupling Frequency ........................................................................................ 8

Dialog Normalization ....................................................................................... 9

Dialog Normalization Channel 2 ..................................................................... 9

Enable Low-Frequency Effects ....................................................................... 9

Bitstream Info Property Page..................................................................... 9

Center Mix Level ............................................................................................. 9

Surround Mix Level ......................................................................................... 9

Dolby Surround Mode ................................................................................... 10

Copyright Bit .................................................................................................. 10

Original Bit Stream ........................................................................................ 10

Info Exists ...................................................................................................... 10

Mix Level ........................................................................................................ 10

Figure 2. Bitstream Info Property Page ................................................................. 10

Room Type ..................................................................................................... 11

Channel 2 Info Exists, Channel 2 Mix Level, Channel 2 Room Type ........... 11

Preprocessing Property Page .................................................................. 11

Digital De-emphasis ...................................................................................... 11

DC High-pass Filter ....................................................................................... 11


4/16

Bandwidth Low-pass Filter ............................................................................ 11

LFE Low-pass Filter ...................................................................................... 12

90-Degree Phase Shift .................................................................................. 12

3 dB Attenuation ............................................................................................ 12

Figure 3. Preprocessing Property Page ................................................................ 12

Compression Characteristic .......................................................................... 13

RF Overmodulation Protection ..................................................................... 13

Input/Output Property Page ..................................................................... 13

Input Channel Assignments .......................................................................... 13

Figure 4. Input/Output Property Page .................................................................... 13

Output Mode .................................................................................................. 14

Stream Number ............................................................................................. 14

Time Codes ................................................................................................... 14

Audio Output .................................................................................................. 14

File Format .................................................................................................... 14

Playback Clock Source ................................................................................. 14

Block Diagram ........................................................................................... 14

Typical Installation .................................................................................... 14

Figure 5. AC-3 Encoder Block Diagram ................................................................. 15

Figure 6. Typical Installation Layout ....................................................................... 15

Contents (Cont)

Rev. 0, Feb 2002Copyright 2002, Vela LP


5/16

Dolby Digital / AC-3

Encoding Using theArgus Encoder

IntroductionThe ability to encode an Dolby Digital/AC-3 stream in addition to the

standard MPEG audio and video streams is an optional feature availablewith Velas 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 audio

processor 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 cable

A 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 that

shows the Momentum board in a typical Argus encoder configuration iscan be found in Figure 6.

Getting Started

In 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.


6/16

Dolby Digital / AC-3 Encoding Using the Argus Encoder6

Connect the supplied input/output cable to the boards D-connector.

Install the software for the Momentum Dolby Digital/AC-3

encoder, making sure that the Momentum microcode is located inthe directory from which the FMTestApp (or EDL Editor) applica-

tion is 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\Broadcast

Argus\EncoderConfig\AC3Installed is set to 1.

Before cueing for an encode, use the Dolby Parameter Control

Application 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 be

set using the Dolby Parameter Control Application. The one notable ex-

ception to 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 set

using 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 Page

It is from the Configuration Control property page (Figure 1) that you

turn Dolby Digital/AC-3 encoding on or off and that you set the bit rate

and sample rate of the AC-3 stream. The following properties are repre-sented on the Configuration Control page:

Dolby Enabled

Check this checkbox if and only if you wish to include a Dolby Digital/AC-3 stream in the next encoded file.

Time Code Start

Check this checkbox if and only if you wish to use the mark-in and mark-out

of 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 EDL

Editor or the VTR property page on RegCtrlPnl to enable VTR control.


7/16

Dolby Digital / AC-3 Encoding Using the Argus Encoder 7

2. The Momentum board must be supplied with a time-code input signal.For example, the time-code-out of the tape deck might be connected

to the time-code-in cable supplied with the Momentum encoder.

3. The mark-in and mark-out supplied through the EDL Editor or through

RegCtrlPnl must be valid time codes that will be provided to the

Momentum encoder by the time-code generator.

4. Prior to the encode, the tape must be pre-rolled to a point well ahead of

the mark-in.

Start Delay

The numeric value in this field specifies the number of milliseconds thatthe Argus encoder will wait after starting the Momentum encoder before

starting 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 au-dio and video encoders will be started before the Momentum

encoder is started. This value can be adjusted to guarantee propersynchronization of the video and Dolby Digital/AC-3 content.

Data Rate

This field specifies the speed in kilobits per second at which the Dolby

Figure 1. Configuration Control Property Page


8/16


Digital/AC-3 data will be transmitted. Values range from 32 kbps to 640

kbps. Data rates that are supported by the encoder depend on the selected

audio coding mode (see below). Generally speaking, the fewer the chan-nels included in the bit stream, the lower the data rate.

Sample Rate

The sample rate field specifies the transmission frequency of the Dolby

Digital/AC-3 bit stream. Because the Momentum encoder does not

include a sample rate converter, you should in most cases check theAuto checkbox next to the sample rate field, thereby slaving the sample

rate to that of the input signal.

Audio Coding Mode

This field specifies the number and configuration of full-bandwidth au-

dio channels to be encoded within the AC-3 bit stream. The audio coding

mode is designated as two numbers, m and n, where m is the number offront channels and n is the number of rear (or Surround) channels. The

exception to this notation is the 1+1 selection, representing dual-mono,

where two completely separate channels are included in the bit stream.

Audio Bandwidth

The bandwidth of the audio is adjusted automatically by the Momentumencoder, which usually maintains the full audio spectrum bandwidth of

20 kHz. In some cases, however, especially where the audio data rate is

decreased to an exceptionally low value, it may be useful to decrease theaudio bandwidth as well. The optimum choice of audio bandwidth

depends on both the audio coding mode and the data rate. In most cases,

you should allow the encoder to adjust the audio bandwidth automati-

cally (just check the Auto checkbox).

Bit Stream Mode

This parameter identifies the type of service that the Dolby Digital/AC-3bit stream conveys. Its setting does not affect the encoding process, but

merely provides vendor-specific information to the decoder.

Coupling Frequency

This parameter identifies the frequency at which the encoder starts touse high-frequency channel coupling. The setting is ignored if theaudio coding mode is 1+1 or 1/0. In most cases, you should allow the

encoder to adjust the coupling frequency automatically (just check

the Auto checkbox).


9/16


Dialog Normalization

This parameter allows for uniform reproduction of spoken dialog when

decoding 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 repro-

duction system to set the audio reproduction volume.

Dialog Normalization Channel 2

This parameter serves the same purpose as the Dialog Normalizationsetting, described above; however, it applies to the second channel of a

dual-mono bit. It is ignored if the audio coding mode is not 1+1.

Enable Low-Frequency Effects

This setting enables or disables the optional low-frequency effects chan-

nel. This LFE channel of limited bandwidth (


10/16


Dolby Surround Mode

This setting specifies whether or not a two-channel Dolby digital bit stream

is conveying a Dolby Surround encoded program. This parameter

appears in the bit stream only when the audio coding mode is set to 2/0.

Copyright Bit

The setting of this checkbox indicates whether or not the included audio

content is protected by copyright.Original Bit Stream

The setting of this checkbox specifies whether the AC-3 content is an

original bit stream (checked) or just a copy of the original (unchecked).

Info Exists

This setting specifies whether or not audio production information(mixing level and room type) exist within the AC-3 bit stream.

Mix Level

Active only when the Info Exists checkbox is checked, this setting indi-

cates the absolute acoustic Sound Pressure Level (SPL) of an individual

channel (usually the center channel dialog level) during the final audio

Figure 2. Bitstream Info Property Page


11/16


mixing 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 reaches

digital 100% full scale (0 dBFS) in the PCM representation. The absoluteSPL is typically measured using pink noise at -20 or -30 dB RMS with

respect to the peak RMS sine wave level. The Mix Level value is not

normally used within the Dolby Digital decoder, but may be used by

other elements in an audio system. This setting appears in the stream

only when the Info Exists checkbox is checked.

Room Type

This setting indicates the type and calibration of the room used for the finalaudio mixing session. It is not normally used within the Dolby Digital

decoder, but may be used by other elements in an audio system. This setting

appears in the stream only when the Info Exists checkbox is checked.

Channel 2 Info Exists, Channel 2 Mix Level, Channel 2 Room Type

These 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 audio

coding 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 Page

The settings on the Preprocessing property page (Figure 3) control themanner in which the incoming PCM data is processed before being sent

to the encoding algorithm.

Digital De-emphasisWhen an incoming PCM signal has been digitally emphasized, it is

usually advisable to de-emphasize that signal before encoding it. If you

check the Auto checkbox, the AC-3 encoder will decide, based on theincoming audio, whether or not to apply de-emphasis.

DC High-pass Filter

This checkbox either enables (checked) or disables a DC filter for all

input channels.

Bandwidth Low-pass Filter

This checkbox either enables (checked) or disables a low-pass filter forall input channels.


12/16


LFE Low-pass Filter

This setting is used to activate a 120 Hz low-pass filter applied to the LFE

input channel. If the digital signal fed to the LFE input does not contain

information above 120 Hz, you may disable this filter.

90-Degree Phase Shift

This feature is used to generate multichannel AC-3 bit streams that maybe down-mixed in an external two-channel decoder to create an output

that is truly compatible with Dolby Surround.

3 dB Attenuation

This setting applies a 3 dB cut to the Surround channels of a multi-

channel film sound track when it is being transferred onto a formatfor consumer home theater playback. This feature is available because

cinema sound track Surround channels are mixed 3 dB hot relative

to the front channels in order to account for cinema amplifier gains.Home theater Surround gains are calibrated differently, thus

requiring a -3 dB adjustment to the Surround tracks.

Figure 3. Preprocessing Property Page


13/16


Figure 4. Input/Output Property Page

Compression Characteristic

This setting specifies the characteristic curve of the Dynamic Range

Compression algorithm. If the compression characteristic setting is enabledduring the encode, a Dolby decoder will refer to this setting to reduce the

audio program's dynamic range. Available selections for this parameterinclude Film Standard, Film Light, Music Standard, Music Light, and Speech.

RF Overmodulation Protection

This setting determines whether or not a RF preemphasis filter is used to

prevent RF over-modulation in set-top-box decoders.

Input/Output Property PageThe Input/Output property page allows you to control parameters directly

related to the incoming and outgoing digital signals. See Figure 4.

Input Channel Assignments

The six controls in the left-most column (labeled Input Channel Assign-ments) allow you to associate each of the six input channels with a specific

channel 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.


14/16


Output Mode

The data signal sent by the encoder has an information field specifying

what format the data is in. The options are: (1) Consumer-Professional32-bit, (2) Professional 16-bit channel 1, and (3) Professional 16-bit

channel 2. A Dolby Digital/AC-3 decoder will use this value in a vendor-specific manner.

Stream Number

This setting specifies the data stream number to be inserted into the

preamble of the IEC958 AC-3 output data. The valid range for thisparameter is 0 through 7, with a default value of 0.

Time Codes

This settings specifies whether or not SMPTE time code packets are to be

included in the encoder output.

Audio Output

This parameter determines the value of bit 1 (the audio/non-audio bit) of

the channel status information contained in the IEC958 output. Annex B

of ATSC A/52 recommends setting this bit to 1 (non-audio data) inprofessional mode to indicate the presence of AC-3 data within the IEC

958 interface. The bit must be set to 1 in the consumer mode.

File Format

This parameter is used in determining the format of recorded disk files.

Playback Clock Source

This parameter determines the source of the master audio clock during

playback from a disk file. When this parameter is set to Internal Synchro-nization (0), the encoder will use one of the on-board oscillators,matching the detected sampling frequency of the disk file. When the clock

source parameter is set to External Synchronization (1), the encoder uses

the recovered clock from the digital input signal.

Block Diagram

The illustration in Figure 5 shows system flow within the Dolby Digital/

AC-3 encoder, the system PCI bus, and the Vela Argus encoder.

Typical Installation

Figure 6 shows the Momentum Opus Dolby Digital/AC-3 encoder board

as typically installed in a Vela Argus rack-mount encoder system.


15/16


Figure 5. AC-3 Encoder Block Diagram

Figure 6. Typical Installation Layout


16/16

Broadcast Products Division

404 West Ironwood DriveSalt Lake City, UT 84115801-464-1600

OEM Products Division

5733 Myerlake CircleClearwater, FL 33760727-507-5300

www.vela.com

vela momentum user manual

Documents