SERVES

Consistent audio levels from every digital receiver.
The AC-3 audio standard adopted by the FCC for DTV requires proper setting of the encoder dialnorm parameter. If this is done by every station, program loudness will be consistent from channel to channel. Casual measurements in several markets indicate grossly improper dialnorm settings at some stations. The cooks need to mind the kitchen! See Understanding Dialnorm.

Improved audio to every digital receiver.
All digital cable set-top boxes and DTV receivers benefit from the increased headroom, reduced noise, and absence of pre-emphasis limiting made possible by the DTV AC-3 audio standard. See Dynamic Range Control.

5.1 audio to consumers with digital reception and a Dolby Digital decoder.
All digital cable set-top boxes and DTV receivers have a Dolby Digital output suitable for connection to the large and growing number of consumer Dolby Digital surround-sound amplifiers.

Multiple secondary audio services to consumers with a compatible DTV receiver.
Modern DTV receivers allow the user to cycle through multiple audio services associated with a single video program. Choices can include Video Description and additional language tracks. Unfortunately, digital-cable set-top boxes typically can only access the single secondary audio service pre-selected at the cable head-end.

These flavors of station DTV audio implementation require a PSIP system and a DTV transmitter. An EPG system is optional. (See recipes for DTV PSIP and DTV EPG.) All provide FCC-compliant EAS and ID local insertion.

A means of measuring dialnorm is essential.

• Dolby LM100 Broadcast Loudness Meter

They also require satellite reception with ATSC decoding capability (except Flavor 2 which requires only a satellite demod). See ATSC Satellite Decoders for a list of equipment in use at various PBS stations, with a feature comparison.

• Digital Vision Bitlink HD/SD IRD
• Sencore IRD3384 HD/SD IRD
• TandbergTV PMRX5800 HD IRD

We presume that PBS will continue to deliver multiple SD and HD programs as ATSC streams. Each stream includes two Dolby Digital services (2 audio PIDs) with a data rate of 384 Kbits/second. These services both have the "Film Standard" compression profile for "Line Mode" and "RF Mode" and a dialnorm value of -27. (PBS follows the SMPTE digital audio level reference of -20 dBFS on the encoder inputs.)

The first audio PID is normally 2/0 stereo. When a program is delivered for the HDTV feed with 5.1 surround, this PID is switched to the 3/2LFE mode and the producer dialnorm and other metadata is used. PBS accepts HDCam with LtRt on tracks 1/2 and Dolby E-encoded 5.1+VideoDescription+Spanish+Metadata on tracks 3/4.

The second audio PID is 2/0 with Video Description or a mono mix on the left channel, and Spanish or a mono mix on the right channel.

All flavors require careful testing on a variety of consumer equipment and coordination with each cable company carrying the DTV stream.

Flavors 3-5 will require further investigation to determine if the MPEG data rate can be changed dynamically to accommodate 5.1 surround, or if the full rate must always be reserved.

All variations but Flavor 2 require familiarity with dialnorm and DRC. It is also helpful to compare LAeq readings with PPM and VU readings to gain a sense of the relationship between these differing modes of measurement. See Understanding dialnorm, NTSC Audio Levels, and Dynamic Range Control.

While this option does not provide 5.1 audio, it is worth including because it provides simultaneous DVS & Spanish, and an evolutionary path towards wider dynamic range for all programs including those multicast. By using the full headroom of digital VTRs, a 10 dB increase in peak dynamic range is provided to consumers with digital cable and off-air DTV reception.



Ingredients
Four-channel servers, digital VTRs and master control. Four-channel router or embedded audio.

Advantages
Supports traditional program time delay, ID, EAS and promotional insertion on all channels. Integrates easily with NTSC services. Increases peak dynamic range 10 dB for consumers with digital reception.

Disadvantage
Concatenation of Dolby Digital encoding. (The degree of audibility of this is uncertain.)

Instructions
Configure the equipment as shown. Perform Encoder and Multiplexer Configuration.

Adjust the satellite receiver output gain to produce dialog levels consistent with internal plant levels and turn off Dynamic Range Control. Provide overload protection for connections to analog equipment. (Initially, this will be needed only for network programs delivered in wide-range 5.1 audio.) Optionally, provide mild AGC audio pre-processing for the DTV channels. Set encoder dialnorm to the measured dialog level at the encoder input (equal to plant dialog level if no pre-processing is employed.)

Provide automated switching as shown to select between Video Description and Spanish for the NTSC SAP channel. Add additional switching within master control if archival material or other sources do not follow the four channel convention.

Help convince all stations to implement this approach so that PBS can relax it's peak audio level restrictions for stereo submission. Doing so would allow producers and stations to deliver wider dynamic range to all consumers with digital reception.

Ingredients
Bitstream processor with options.

• Leitch/Agilevision Bitstream Processor

Advantages
Delivers 5.1 audio, secondary audio and metadata as intended by the producer, without any action by the broadcaster. Avoids concatenating the Dolby Digital signal. No separate PSIP system needed. Has options for channel drop & add, local channel insertion, bit-rate reduction, EAS audio/video insertion, Bug insertion, bitstream storage and playback, and stream splicing. All this is provided in one system with a single vendor responsible for interoperability.

Disadvantages
All functions are in a single system. Incompatible with possible network shift to Dolby E. No VOCA feature.

Instructions
Select from the many optional features when purchasing. Install the system and perform Encoder and Multiplexer Configuration as needed for alignment to plant levels.

click image to view starter system

Ingredients
ID/Bug/EAS inserter. Satellite IRD with AC-3 output.

• DP569 Dolby Digital Encoder

Optional Ingredients
Optional ingredients are shown without borders. If the extra sources and the 10x1 switcher are used, it is simpler to use embedded audio interconnection. An ASI server with attached ATSC decoder makes it possible to time-delay network programming.

An upconverter allows switching to local standard definition sources. An HDTV VTR can be added. If either of these sources with PCM audio are included, a 230 ms AC-3 delay and associated switching must be provided for reasons described in the instructions below. A Dolby frame synchronizer may be required to prevent main audio click at the switch point.

Advantages
Delivers 5.1 audio, secondary audio and metadata as intended by the producer without any action by the broadcaster. Additional features can be added incrementally. Avoids concatenating the Dolby Digital signal.

Disadvantages
No VOCA mix possible over network 5.1 shows. No obvious location for PCM audio processing, without also disturbing Dolby Digital signals. Incompatible with possible network shift to Dolby E.

Instructions
Configure the equipment as shown. Configure the satellite IRD for embedded Dolby Digital on the main audio service. Perform Encoder and Multiplexer Configuration.

If no local video sources are provided (and no 210 ms delay), configure the MPEG encoder/multiplexer AC-3 input for -10 ms of coding delay compensation (if it goes that low). This value is appropriate because this approach introduces no coding or decoding delay. (A receiver Dolby Digital output is 10 ms ahead of the video, to allow for decoding latency.) This will result in EAS audio being 200 ms late, but with no associated video, it is of no concern.

On the other hand, if local audio/video sources like up-converters or HD VTRs are used, local lip sync is critical. The MPEG encoder/multiplexer AC-3 input must be set to 200 ms of coding delay compensation for the latency within the Dolby Digital encoder. When this encoder is bypassed for network or server AC-3 pass-through, 210 ms of delay must be introduced to keep the network lip sync correct.

Ingredients
Eight-channel servers and VTRs such as DVCPro-HD or HD-D5. Master Control switcher with eight channels of audio. Eight-channel router, or embedder on each decoder output and two de-embedders on the master control A/B inputs.

• DP564 Dolby Digital Decoder
• DP569 Dolby Digital Encoder

Advantages
Provides VOCA and video mix capabilities. Provides a natural path towards network adoption of Dolby E. (Replace satellite Dolby Digital decoders with Dolby E decoders.)

Disadvantages
Concatenation of Dolby Digital encoding. (The degree of audibility of this is uncertain.) No metadata path, requiring automation control of the encoding mode. No provision for compression external to the Dolby Digital system for archival stereo sources. No direct access to a LtRt downmix from VTR or server for dubbing to stereo and monitoring.

Instructions
Configure the equipment as shown. Perform Encoder and Multiplexer Configuration. Turn off DRC in the Dolby Digital Decoder. Add gain with a DA to to raise dialog levels from -31 LAeq to the historic average plant dialog levels. Set the encoder dialnorm value to this same plant level. Implement traffic and automation systems to track programs produced in 5.1 audio and to switch encoder modes.

This is similar to Flavor 4, but can also use four-channel servers and VTRs (like HDCam).

Ingredients
One Dolby E encoder for each satellite receiver and two Dolby E decoders for master control A/B switching. Additional Dolby E encoders for local production and decoders for monitoring. One-frame video and audio delays to compensate for Dolby E encoding and decoding latency.

• DP564 Dolby Digital Decoder
• DP571 Dolby E Encoder
• DP572 Dolby E Decoder
• DP569 Dolby Digital Encoder

Four-channel servers and VTRs. Master Control switcher with eight channels of audio. Eight-channel router, or embedder on each decoder output and two de-embedders on the master control A/B inputs.

Advantages
Provides VOCA and video mix capabilities. Provides a natural path towards network adoption of Dolby E. (Replace satellite Dolby Digital decoders with Dolby E decoders.) The LtRt downmix is available in the router for stereo dubs.

Disadvantages
Concatenation of Dolby Digital encoding. (The degree of audibility of this is uncertain.) No metadata path, requiring automation control of the encoding mode. No provision for compression external to the Dolby Digital system for archival stereo sources. No direct access to a LtRt downmix from VTR or server for dubbing to stereo and monitoring.

Instructions
Configure the Dolby E system. Note that the metadata-passing feature of Dolby E cannot be used, because the Dolby Digital decoder does not have a metadata output. (If PBS were to offer Dolby E, this could change, but the master control switcher would need to both switch the metadata and adjust the level of VOCAs to match the dialnorm of the current show.)

Configure the equipment as shown. Perform Encoder and Multiplexer Configuration. Turn off DRC in the Dolby Digital Decoder. Add gain with a DA to to raise dialog levels from -31 LAeq to the historic average plant dialog levels. Set the encoder dialnorm value to this same plant level. Implement traffic and automation systems to track programs produced in 5.1 audio and to switch encoder modes.

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