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Using the Transcoder

Setting Up the Transcoder

LA-5291 supports a variety of decoding, transcoding, and encoding options, including:

Decoding Dolby® ED2 streams to PCM
Transcoding Dolby ED2 streams to Dolby Digital Plus JOC and Dolby E streams to Dolby Digital Plus
Encoding PCM audio to Dolby Digital Plus, Dolby Digital Plus JOC, and Dolby ED2

Transcoding Basics

The name of the program being transcoded can be customized by clicking on the Program 1 name box (1A), typing a name, and clicking the green checkmark.

The LA-5291 supports three different workflows, selectable in the Workflow dropdown menu (1B), including:

Dolby Digital Plus Atmos (Dolby Digital Plus JOC) transcoding
Dolby ED2 encoding
Dolby ED2 decoding

Note that certain settings may be grayed out if they are not applicable to the selected workflow.

Note - It is assumed that the signal being fed into the LA-5291 is appropriate for the selected workflow. For example, if the “Dolby ED2 Decoding” workflow is selected, the unit expects to see a Dolby ED2 or Dolby E bitstream at its input.

When the input source is a Dolby ED2 bitstream, the Presentation menu (1C) selects which of the presentations found in the Dolby Atmos metadata are encoded to the output stream.

The Encoding Mode dropdown (1D) determines the channel format of the encoded output. When set to “External Metadata”, the metadata values as presented by a Dolby DP590 connected to the Control Ethernet port of the LA-5291 will be used. If no metadata is present, or if a different channel output format is required, the output can be encoded as 2.0, 5.1, 5.1.4, or 7.1.4.

Incoming audio channel mapping for the various encoding modes is shown in the table below, where "rs" indicates "rear surround," "tm" indicates "top middle," "tf" indicates "top front," and "tr" indicates "top rear."

Note - Scroll left and right on the table below to see additional channels.

When the “DD+ Atmos Transcoding” workflow is selected, the Data Rate dropdown (1E) lists all available encoding data rates supported by the current Encoding Mode.

The Dialog Normalization dropdown (1F) is used to select the dialnorm metadata value.

Advanced Transcoder Controls

Clicking on the Advanced down arrow (7-2A) expands the Advanced menu for the transcoder.

As in the basic transcoder menu, certain settings will be grayed out if they are not applicable to the currently selected workflow. Specifically:

When the “DD+ Atmos Transcoding” workflow is active, the “ED2 Frame Rate” control is grayed out
When the “ED2 Encoding” workflow is selected, all advanced controls except the “ED2 Frame Rate” are grayed out
When the “ED2 Decoding” workflow is active, all advanced controls are grayed out

The dynamic range compression profiles for Line Mode (2B) and RF Mode (2C) are independently selectable and include Film Standard (the default mode), Film Light, Music Standard, Music Light, and Speech.

The Dolby Surround Mode (2D) identifies to the decoder that a 2-channel output is either PCM stereo (“Not Encoded”) or matrix surround-encoded (“Encoded”). If it is not necessary to indicate the mode at all, select “Not Indicated”.

Enabling Surround Phase Shift (2J) adds a 90-degree phase shift filter to one surround channel to de-correlate the surrounds and prevent channel buildup during the downmixing process. It is recommended this be set to the default value of “Enabled.”

The preferred downmix type is selected with the Preferred Stereo Downmix Mode control (2I).

An Lt/Rt downmix sums the surround channels and adds them to the left channel (in phase) and the right channel (out of phase) which allows an AVR with a Dolby Pro Logic decoder to reconstruct the Left, Center, Right, and mono Surround (Pro Logic), or Left, Center, Right, and stereo Surround channels (Pro Logic II)
A Lo/Ro downmix simply adds the Left and Right surround signals to the Left and Right stereo channels respectively, and is appropriate for stereo-only listening and where delivering a mono-compatible signal is important

The Surround Trims control (2H) and Height Trims control (2G) adjust the amount of attenuation to their respective channels applied in the decoder.

When the Surround Duplication control (2F) is enabled, the incoming audio is in 5.1-channel format, and the desired output is 7.1, the encoder will copy the Left Surround (Ls) audio to the Left Rear Surround (Lrs) channel, and the Right Surround (Rs) audio to the Right Rear Surround (Rrs) channel.

The ED2 Frame Rate control (2E) sets the frame rate to either 25 or 29.97 when using the “ED2 Encoding” workflow. This should be set to match the frame rate of the accompanying video signal, or ½ of the frame rate if the accompanying video signal is 50 or 59.94 Hz.

Decoder Metadata Screen

The Decoder screen (3A) shows various values of the incoming Dolby ED2 or Dolby E bitstream. The displayed values will vary depending upon which bitstream type is preset.