A Guide to Dolby Metadata

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Metadata provides unprecedented capability for content producers to deliver the highest quality audio to consumers in a range of listening environments. It also provides choices that allow consumers to adjust their settings to best suit their listening environments.

In this article, we will cover:

Metadata overview
Dialogue level
Dynamic Range Control (DRC)
Downmixing
Individual metadata parameters

Metadata Overview

Dolby Digital, Dolby Digital Plus, Dolby AC-4, Dolby E and Dolby ED2 are all bit-rate reduction technologies that use metadata to describe the encoded multichannel audio. In normal operation the encoded audio and metadata are carried together as a data stream on two regular digital audio channels (AES/EBU or S/PDIF). The metadata describes the encoded audio and conveying information that precisely controls downstream encoders and decoders. With Dolby ED2 the encoded audio may be split across multiple bitstreams (i.e. with immersive audio applications) or it may be carried on an additional pair of audio channels if desired. Metadata allows content providers unprecedented control over how original program material is reproduced in the home or on mobile devices.

Dolby Digital, Dolby Digital Plus and Dolby AC-4 are transmission bitstreams (sometimes called an emission bitstream) intended for delivery to the consumer. They consist of a single encoded program of up to eight channels described by one metadata stream. The consumer's decoder processes the metadata stream according to parameters set by the program creator, as well as certain settings for bass management and dynamic range that are chosen by the consumer to reflect their specific reproduction equipment and environmental conditions.

Dolby E and Dolby ED2 are distribution bitstreams capable of carrying up to eight channels of encoded audio and metadata per digital channel pair. The number of programs ranges from one single program (Program Config: 5.1) to eight individual programs on a single Dolby E stream (Program Config: 8 x 1) and full Dolby Atmos and immersive audio support with Dolby ED2. Each program is discrete with its own metadata in the bitstream. Some control metadata parameters in a Dolby E and Dolby ED2 stream automatically configure a Dolby Digital/Dolby Digital Plus/Dolby AC-4 encoder while others are passed through to the consumer's decoder.

Dolby E and Dolby ED2 are professional technologies used for broadcast applications such as program origination and distribution. The bitstream carries the entire metadata parameter set. Transmission bitstreams employ a subset of the entire metadata parameter set called Dolby Digital/Dolby Digital Plus/Dolby AC-4 metadata; the transmission bitstream carries only those parameters necessary for proper decoding by the consumer.

Metadata is first inserted during program creation or mastering, and is carried through transmission in a broadcast application, video on demand or directly onto physical media. The metadata provides control over how the encoded bitstream is treated at each step on the way to the consumer's decoder.

For example:

In a broadcast truck parked outside a football stadium, the program mixer chooses the appropriate metadata for the audio program being created. The resulting audio program, together with metadata, is encoded as Dolby E/Dolby ED2 and sent to the television station via fiber, satellite, or other transmission link. At the receiving end of this transmission, the Dolby E/Dolby ED2 stream is decoded back to baseband audio and metadata. The audio program is monitored and the metadata is altered or re-created as other elements of the program are added in preparation for broadcast. This new audio program/metadata pair is re-encoded as Dolby E/Dolby ED2, leaves the postproduction studio and is passed through the television station to Master Control, where many incoming Dolby E/Dolby ED2 streams are once again decoded back to their individual baseband digital audio/metadata programs. The audio program/metadata pair that is selected to air is sent to the transmission Dolby Digital/Dolby Digital Plus/Dolby AC-4 encoder, which encodes the incoming audio program according to the metadata stream associated with it, thereby simplifying the transmission process. Finally, the transmission bitstream is decoded in the consumer's device, with metadata providing the information for that decoding process. Through the use of metadata, the mixer in the truck has been able to control the consumer's decoder for the sporting event, while news breaks, commercials, station IDs, and the like are similarly appropriately decoded.

This control, however, requires the producer to correctly set the metadata parameters because they affect important aspects of the audio — and can seriously compromise the final product if set improperly. Although most metadata parameters are transparent to consumers, certain parameters affect the output of a consumer decoder, like when downmixing for a specific speaker configuration, or when the consumer chooses Dynamic Range Control to avoid disturbing family and neighbours.

In the simplest terms, there are two functional classifications of metadata:

Informational: These parameters convey information but do not affect either the encoded bitstream or the decoding process. For example, the Bitstream Mode parameter describes the audio service provided in the bitstream according to the ATSC specification; this information may be used by certain components in the audio system.

Control: These parameters direct how the decoder, encoder, or both process the audio when certain modes are applied to the encoder or decoder. For example, the Lowpass Filter parameter determines whether a lowpass filter is applied to the main inputs of a Dolby bitstream encoder, and the Surround Downmix Level parameter instructs the Dolby bitstream decoder how to mix the surround channels during downmixing.

Table 1: Metadata Parameters

Extended Bitstream information parameters are in italics

Dialogue Level

Dialogue level (also known as dialogue normalization or dialnorm) is perhaps the single most important metadata parameter. The dialogue level setting represents the average loudness of dialogue in a presentation.

When received at the consumer's decoder, this parameter setting determines the level shift in the decoder that sets, or normalizes, the average audio output of the decoder to a preset level. This aids in matching audio volume between program sources.

The proper setting of the dialogue level parameter enables the Dynamic Range Control profiles chosen by the content producer to work as intended in less-than-optimal listening environments, and is essential in any content production, whether it is for transmission in a broadcast stream, video on demand or for direct distribution to consumers via physical media.

In broadcast transmission and video on demand, standard setting of dialogue level ensures that the consumer can switch channels or watch a television program without having to adjust the volume control during commercial breaks or between different content. Using that standard for all content, whether conveyed by broadcast television, video on demand or physical media, enables the consumer to switch between sources and programs while maintaining a comfortable listening level.

Note: Programs without dialogue, such as an all-music program, still require a careful setting of the dialogue level parameter. When setting the parameter for such content, it is useful to compare the program to the level of other programs. The goal is to allow the consumer to switch to your program without having to adjust the volume control.

The Scale

The scale used in the dialogue level setting is from –1 to –31 dB in 1 dB steps. Contrary to what you might assume at first, a setting of –31 represents no level shift in the consumer's decoder, and –1 represents the maximum level shift. Here's why: consumer decoders standardize the average loudness (averaged over time by the formula LeqA) to –31 dBFS (31 dB below 0 dB full-scale digital output) by applying a shift in level based on the dialogue level parameter setting. When a decoder receives an input signal with a dialogue level setting of –31, it applies no level shift to the signal because this indicates to the decoder that the signal already matches the target level and therefore requires no shift. In contrast, a louder program requires a shift to match the –31 dB standard. When the dialogue level parameter setting is –21, the decoder applies a 10 dB level shift to the signal. When the setting is –11, it applies a 20 dB level shift, and so on.

A simple rule: 31 + (dialogue level value) = shift applied.

Example: 31 + (–21) = 10 dB.

The most important point to remember is that in setting the dialogue level parameter, you are providing your listener with an essential service. For your listeners, setting this level properly means:

The volume level is consistent with other content.
The DRC profiles you make available to them work as you intend.

Once dialogue level is set, you can set up DRC profiles to further benefit the consumer.

Dynamic Range Control

Different home listening environments present a wide range of requirements regarding dynamic range. Rather than simply compressing the audio program to work well in the poorest listening environments, Dolby bitstream encoders calculate and send Dynamic Range Control (DRC) metadata with the signal. This metadata can be applied to the signal by the decoder to reduce the signal's dynamic range. Through the proper setting of DRC profiles during the mastering process, the content producer can provide the best possible presentation of program content in virtually any listening environment, regardless of the quality of the equipment, number of channels, or ambient noise level in the consumer's home.

Many decoders offer the consumer the option of defeating the Dynamic Range Control metadata, but some do not. Decoders with surround outputs (full 5.1/7.1-channel capability) typically offer this option. Decoders with stereo, mono, or RF-remodulated outputs, such as those found on DVD players and set-top boxes, often do not. In these cases the decoder automatically applies the DRC metadata associated with the decoder's selected operating mode.

The bitstream carries metadata for the two possible operating modes of the decoder. The operating modes are known as Line Mode and RF Mode due to the type of output they are typically associated with. Line Mode is typically used on decoders with two-channel or higher line-level outputs and RF Mode is used on older decoders that have an RF-remodulated output. Full-featured decoders allow the consumer to select whether to use DRC and if so, which operating mode to use. The consumer sees options such as Off, Light Compression, and Heavy Compression instead of None, Line Mode, and RF Mode. Advanced decoders may also allow custom scaling of the DRC metadata. All that needs to be done during encoding is selection of the dynamic range control profiles for Line Mode and RF Mode.

Note: While the use of DRC modes during decoding is a consumer-selectable feature, the dialogue level parameter setting is not. Therefore, the proper setting of the dialogue level parameter is essential before previewing a DRC profile.

Line Mode

Line Mode offers these features:

Low-level boost compression scaling is allowed
High-level cut compression scaling is allowed when not downmixing
Dialogue, as set by the dialogue level parameter, is reproduced at a constant level of –31 dBFS LAeq.

All line-level or power-amplified outputs from set-top decoders, digital televisions, and A/V surround decoders use Line Mode.

Consumer control of the dynamic range is limited when downmixing. Products with stereo or mono outputs do not usually allow consumer scaling of Line Mode, because these devices are usually downmixing (for example, when receiving a 5.1-channel signal). However, in these products the consumer may have a choice between Line Mode and RF Mode.

RF Mode

RF Mode offers these features:

High- and low-level compression scaling is not allowed (when active, always fully applied).
+11 dB gain shift raises overall program level.
Dialogue, as set by the dialogue level parameter and combined with the +11 dB gain shift, is reproduced at a constant level of –20 dBFS LAeq.

RF Mode is designed for products (such as set-top boxes) that generate a downmixed signal for connection to the RF/Antenna input of a television set; however, it is also useful in situations where heavy DRC is required. In RF Mode, the overall program level is raised 11 dB, while the peaks are limited to prevent signal overload in the D/A converter. By limiting headroom, severe overmodulation of television receivers is prevented. The 11 dB gain provides an RF modulation level that compares well with analog television broadcasts and premium movie channels. In some situations it may be necessary to further constrain signal peaks above the average dialogue level so that there is less than 20 dB headroom. The selection of a suitable RF Mode profile achieves this.

Dynamic Range Control Profiles

Six preset DRC profiles are available to content producers: Film Light, Film Standard, Music Light, Music Standard, Speech, and None. Each is applied in the pattern shown in Figure 2. All DRC profiles are encoded using a modified B-weighted curve.

In each case the center of the null band is assigned to the dialogue level parameter setting, and the DRC profile is applied in relation to that level.

Film Light
Max Boost: 6 dB (below –53 dB)
Boost Range: –53 dB to –41 dB (2:1 ratio) Null Band Width: 20 dB (–41 dB to –21 dB) Early Cut Range: –26 dB to –11 dB (2:1 ratio) Cut Range: –11 dB to +4 dB (20:1 ratio)

Film Standard
Max Boost: 6 dB (below –43 dB)
Boost Range: –43 dB to –31 dB (2:1 ratio) Null Band Width: 5 dB (–31 dB to –26 dB) Early Cut Range: –26 dB to –16 dB (2:1 ratio) Cut Range: –16 dB to +4 dB (20:1 ratio)

Music Light (No early cut range)
Max Boost: 12 dB (below –65 dB)
Boost Range: –65 dB to –41 dB (2:1 ratio) Null Band Width: 20 dB (–41 dB to –21 dB) Cut Range: –21 dB to +9 dB (2:1 ratio)

Music Standard
Max Boost: 12 dB (below –55 dB)
Boost Range: –55 dB to –31 dB (2:1 ratio) Null Band Width: 5 dB (–31 dB to –26 dB) Early Cut Range: –26 dB to –16 dB (2:1 ratio) Cut Range: –16 dB to +4 dB (20:1 ratio)

Speech
Max Boost: 15 dB (below –50 dB)
Boost Range: –50 dB to –31 dB (5:1 ratio) Null Band Width: 5 dB (–31 dB to –26 dB) Early Cut Range: –26 dB to –16 dB (2:1 ratio) Cut Range: –16 dB to +4 dB (20:1 ratio)

None
No DRC profile selected. The dialogue level parameter (dialnorm) is still applied.

These choices are available to the content producer for both Line Mode and RF Mode. The content producer chooses which of these profiles to assign to each mode; when the consumer or decoder selects a DRC mode, the profile chosen by the producer is applied.

In addition to the DRC profile, metadata can limit signal peaks to prevent clipping during downmixing. This metadata, known as overload protection, is inserted by the encoder only if necessary. For example, consider a 5.1-channel program with signals at digital full scale on all channels being played through a stereo, downmixed line-level output. Without some form of attenuation or limiting the output signal would obviously clip. Correct setting of the dialogue level and DRC profiles normally prevents clipping and unnecessary application of overload protection.

Note: DRC profile settings are dependent on an accurate dialogue level setting. Improper setting of the dialogue level parameter may result in excessive and audible application of overload protection.

Downmixing

Downmixing is a function of Dolby Digital/Dolby Digital Plus/Dolby AC-4 that allows a multichannel program to be reproduced over fewer speaker channels than for which the program is optimally intended. Simply put, downmixing allows consumers to enjoy high quality content without requiring a full-blown home theatre setup.

As with stereo mixing where the mix is monitored in mono on occasion to maintain compatibility, multichannel audio mixing requires the engineer to reference the mix to fewer speaker channels to ensure compatibility in downmixing situations. In this way, the Dolby bitstream, using the metadata parameters that control downmixing, is an "equal opportunity technology" in that every consumer who receives the bitstream can enjoy the best audio reproduction possible, regardless of the playback system.

When downmixing from multi-channel audio to 2 channel there are 2 options, Dolby Surround and Lo/Ro.

One type is a stereo-compatible Dolby Surround downmix (also called Pro Logic, left-total/right-total, or Lt/Rt) of the multichannel source program that is suitable for Dolby Surround Pro Logic decoding. The other type is a simple stereo representation (called a left-only/right-only, or Lo/Ro) suitable for playback on a stereo hi-fi or on headphones, and from which a mono signal is derived for use on an RF/Antenna output. The difference between the downmixes is how the surround channels are handled. The Lt/Rt downmix sums the surround channels and adds them, in-phase to the left channel and out-of-phase to the right channel. This allows a Dolby Surround Pro Logic decoder to reconstruct the L/C/R/S channels for a Pro Logic home theatre. The use of Pro Logic II decoding adds discrete surround channels for 5.1 playback, Pro Logic IIx adds additional rear speakers for 7.1 surround and Pro Logic IIz adds 2 front height channels.

The Lo/Ro downmix adds the right and left surround channels discretely to the left and right speaker channels. This preserves the stereo separation for stereo-only monitoring and produces a mono-compatible signal. In all downmixes, the LFE channel is not included.

On most consumer devices, the consumer can use the product's user interface to choose the appropriate stereo output for their playback system. The mono signal feeding the RF/Antenna output is always derived from the Lo/Ro downmix.

There are separate metadata parameters for the adjustment of the Lo/Ro and Lt/Rt downmix conditions. Certain metadata parameters allow the engineer to select how the stereo downmix is constructed and which stereo analog signal is preferred, but Lt/Rt is the default selection in all consumer decoders. See 'Parameter Definitions' for more information on individual parameters.

During downmixing, as we have seen, the adjustment of dynamic range control parameters is limited. Broadly speaking, the stereo outputs use the Line Mode compression profile and the mono signal uses RF Mode compression. As with dynamic range control, downmixing is ultimately dependent upon each consumer's unique listening environment.

While the engineer must optimize the multichannel mix for reproduction in an ideal listening environment, it is also important to preview the mix in downmixing conditions to ensure compatibility with different playback systems when selecting the downmixing metadata parameters.

Parameter Definitions

Metadata parameters include:

Universal parameters
Extended Bitstream Information (Extended BSI) parameters

Extended BSI parameters are active only when the consumer's decoder is capable of reading them and when the producer chooses to use them. All decoders can successfully decode a metadata stream without Extended BSI parameters, and Extended BSI parameters translate seamlessly to decoders that read only universal parameters.

Universal Parameters

Universal parameters are present in all Dolby bitstream encoders and decoders.

Dialogue Level

The dialogue level parameter is discussed in 'Dialogue Level'.

Channel Mode

This parameter (also known as audio coding mode) indicates the active channels within the encoded bitstream and affects both the encoder and consumer decoder. This parameter instructs the encoder as to which inputs to use for this particular program; it tells the decoder what channels are present in this program so the decoder can deliver the audio to the correct speakers. The setting is described as X/Y, where X is the number of front channels (Left, Center, Right) and Y the number of rear (surround) channels. The availability of certain channel modes depends on the data rate and whether the LFE Channel is present. For example, you can't have a mono stream with an LFE channel (1.1!) or a 3/2 stream at 96 kbps with Dolby Digital. Note: The presence of the LFE channel is indicated through a different metadata parameter (see LFE Channel).

LFE Channel

The status of the LFE Channel parameter indicates to a Dolby bitstream encoder whether an LFE Channel is present within the bitstream. Channel Mode determines whether the LFE Channel parameter can be set. You must have at least three channels in order to be able to add an LFE channel.

Bitstream Mode

This parameter describes the audio service contained within the Dolby bitstream. A complete audio program may consist of a main audio service (a complete mix of all the program audio), an associated audio service comprising a complete mix, or one main service combined with an associated service. In practice most programming uses the default setting, Complete Main. An example of an exception to this rule would be an emergency service within digital television.

Line Mode Compression Profile

Line Mode is discussed in 'Dynamic Range Control'.

RF Mode Compression Profile

RF Mode is discussed in 'Dynamic Range Control'.

RF Overmodulation Protection

This parameter is designed to protect against overmodulation when a decoded Dolby Digital bitstream is RF modulated. When enabled the Dolby Digital encoder includes pre-emphasis in its calculations for RF Mode compression. The parameter has no effect when decoding using Line Mode compression. Except in rare cases, this parameter should be disabled.

Center Downmix Level

When the encoded audio has three front channels (L, C, R), but the consumer has only left and right front speakers, this parameter indicates the nominal downmix level for the center channel with respect to the left and right channels. Dolby bitstream decoders use this parameter during downmixing in Lo/Ro mode when Extended BSI parameters are not active.

Surround Downmix Level

When the encoded audio has one or more surround channels but the consumer does not have surround speakers, this parameter indicates the nominal downmix level for the surround channel(s) with respect to the left and right front channels. Dolby bitstream decoders use this parameter during downmixing in Lo/Ro mode when Extended BSI parameters are not active.

Dolby Surround Mode

This parameter indicates to a Dolby bitstream decoding product that also contains a Dolby Pro Logic decoder (for example a 5.1-channel amplifier) whether the two-channel encoded bitstream contains a Dolby Surround (Lt/Rt) program that requires Pro Logic decoding. Decoders can use this flag to automatically switch on Pro Logic decoding as required.

Audio Production Information

This parameter indicates whether the mixing level and room type values are valid. If Yes, then a receiver or amplifier could use these values as described below. If No, then the values in these fields are invalid. In practice only high-end consumer equipment implements these features.

Mixing Level

The Mixing Level parameter describes the reference sound pressure level (SPL) that was used during the final mixing session at the studio or on the dubbing stage. The parameter allows an amplifier to set its volume control such that the SPL in the replay environment matches that of the mixing room. This control operates in addition to the dialogue level control, and is best thought of as the final volume setting on the consumer's equipment. This value can be determined by measuring the SPL of pink noise at studio reference level and then adding the amount of digital headroom above that level. For example, 85 dB equates to a reference level of –20 dBFS; the mixing level is 85+20, or 105 dB.

Room Type

The Room Type parameter describes the frequency alignment curve used during the final mixing session at the studio or on the dubbing stage. A Large room is a dubbing stage with the industry standard X-curve alignment; a Small room has flat alignment. This parameter allows an amplifier to set the same equalization as heard in the final mixing environment.

Copyright Bit

This parameter indicates whether the encoded Dolby bitstream is copyright protected. It has no effect on Dolby bitstream decoders and is purely for information.

Original Bitstream

This parameter indicates whether the encoded Dolby bitstream is the master version or a copy. It has no effect on Dolby bitstream decoders and is purely for information.

Note: The parameters DC Filter, Lowpass Filter, LFE Lowpass Filter, Surround 3 dB Attenuation, and Surround Phase Shift appear after the Extended BSI parameters on Dolby E and Dolby Digital/Dolby Digital Plus equipment menus.

DC Filter

This parameter determines whether a DC blocking 3 Hz highpass filter is applied to the main input channels of a Dolby bitstream encoder prior to encoding. This parameter is not carried to the consumer decoder. It is used to remove DC offsets in the program audio and would only be switched off in exceptional circumstances.

Lowpass Filter

This parameter determines whether a lowpass filter is applied to the main input channels of a Dolby bitstream encoder prior to encoding. This filter removes high frequency signals that are not encoded. At suitable data rates this filter operates above 20 kHz. In all cases it prevents aliasing on decoding and is normally switched on. This parameter is not passed to the consumer decoder.

LFE Lowpass Filter

This parameter determines whether a 120 Hz 8th order lowpass filter is applied to the LFE channel input of a Dolby bitstream encoder prior to encoding. It is ignored if the LFE channel is disabled. This parameter is not sent to the consumer decoder. The filter removes frequencies above 120 Hz that would cause aliasing when decoded. This filter should only be switched off if the audio to be encoded is known to have no signal above 120 Hz.

Surround 3 dB Attenuation

The Surround 3 dB Attenuation parameter determines whether the surround channel(s) are attenuated 3 dB before encoding. The attenuation actually takes place inside the Dolby bitstream encoder. It balances the signal levels between theatrical mixing rooms (dubbing stages) and home entertainment or broadcast studios. Home entertainment and broadcast studios are calibrated so that all main channels are at the same sound pressure level (SPL). For compatibility reasons with older film formats, theatrical mixing rooms calibrate the surround channels 3 dB lower in SPL than the front channels. The consequence is that signal levels on tape are 3 dB louder. Therefore, to convert to a consumer mix from a theatrical calibration it is necessary to reduce the surround levels by 3 dB by enabling this parameter. Care should be taken with Dolby Atmos originated content as all Dolby Atmos studios are aligned so that all channels equate to the same SPL.

Surround Phase Shift

This parameter causes the Dolby bitstream encoder to apply a 90-degree phase shift to the surround channels. This allows a Dolby bitstream decoder to create an Lt/Rt downmix simply. For most material the phase shift has a minimal impact when the Dolby bitstream program is decoded to 5.1 channels, but provides an Lt/Rt output that can be Pro Logic decoded if desired. However, for some phase-critical material (such as music) this phase shift is audible when listening in 5.1/7.1 channels. Likewise, some material downmixes to a satisfactory Lt/Rt signal without needing this phase shift. It is therefore important to balance the needs of the 5.1/7.1 mix and the Lt/Rt downmix for each program. The default setting is Enable.

Extended Bitstream Information Parameters

In response to requests from content producers, Dolby Laboratories recently modified the definitions of several metadata parameters from their original definition as described in ATSC document A/52. The original parameters were rarely, if ever used. The revised definitions allow more information to be carried about the audio program and allow more choices for stereo downmixing. When the metadata parameters carried in Dolby bitstream were first described, they were generically called Bitstream Information or BSI. We refer to the alternate parameter definitions as Extended BSI.

Because the revised definitions affect metadata parameters that were not used by the consumer decoders, all decoders will be compatible with the revised bitstream. Newer decoders that are programmed to detect and decode the new parameters will be able to implement the new features the Extended BSI provides.

Preferred Stereo Downmix Mode

This parameter allows the producer to select either the Lt/Rt or the Lo/Ro downmix in a consumer decoder that has stereo outputs. Consumer receivers are able to override this selection, but this parameter provides the opportunity for a 5.1/7.1 channel soundtrack to play in Lo/Ro mode without user intervention. This is especially useful on music material.

Lt/Rt Center Mix Level

This parameter indicates the level shift applied to the center channel when adding to the left and right outputs when downmixing to an Lt/Rt output. Its operation is similar to the center downmix level in the universal metadata.

Lt/Rt Surround Mix Level

This parameter indicates the level shift applied to the surround channels when downmixing to an Lt/Rt output. Its operation is similar to the surround downmix level in the universal metadata.

Lo/Ro Center Mix Level

This parameter indicates the level shift applied to the center channel when adding to the left and right outputs when downmixing to a Lo/Ro output. When Extended BSI parameters are active, this parameter is used and the Center Mix Level parameter in the universal parameters is not.

Lo/Ro Surround Mix Level

This parameter indicates the level shift applied to the surround channels when downmixing to a Lo/Ro output. When Extended BSI parameters are active, this parameter is used, and the Surround Mix Level parameter in the universal parameters is not.

Surround EX Mode

This parameter is used to identify the encoded audio as Surround EX encoded material. This parameter is only used if the encoded audio has two surround channels. An amplifier or receiver with Dolby Digital Surround EX decoding can use this parameter as a flag to switch the decoding on or off automatically. The behavior is similar to the Dolby Surround Mode parameter.

A/D Converter Type

This parameter allows audio that has passed through a particular A/D conversion stage to be marked as such so that a decoder may apply the complementary D/A conversion.

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