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Audio

At a glance

Separate lossless decoding, spatial rendering and output transport. A track can remain uncompressed after decoding without retaining the original Atmos objects at the receiver.

Dolby TrueHD

In short: TrueHD is the lossless sound format on most Dolby-encoded Blu-rays. Like a ZIP file for audio, it makes the track smaller without throwing anything away.9

TrueHD is lossless audio coding. Correct decoding can recover the coded audio presentation without loss from compression. Downmixing, gain, resampling, dynamics processing and bass management occur at other stages and may change samples. UHD Blu-ray can carry Atmos in TrueHD.1

Dolby Atmos and objects

In short: an Atmos track on UHD Blu-ray is not a set of extra sounds that disappear without height speakers. It contains a complete channel version of the same mix. A system without Atmos still plays every sound; what it loses is the placement above and around the listener.

What Atmos is. A studio Atmos mix combines a bed (channels tied to speaker positions, typically for ambience and music) with objects: sounds whose position and movement are described by metadata. A renderer reads that metadata and the room's speaker layout and decides which speakers play each sound.10

What a home disc carries. Before encoding for home delivery, Dolby's spatial coding groups the bed and the studio objects into 12, 14 or 16 signals ("elements"). Bed channels are converted to objects at fixed positions, and nearby objects are merged into clusters; Dolby states that no original object is discarded. A typical TrueHD Atmos bitstream then holds these coded objects together with a 7.1 render of them and 5.1 and stereo downmixes.12 Dolby calls the Atmos part a "fully object-based mix" because the bed travels as objects too, not because the soundtrack lacks a channel foundation.

What plays where:

System What it plays What changes
Atmos receiver with height speakers The coded objects, rendered to all configured speakers Intended path; accuracy still depends on the renderer and speaker setup
Atmos receiver without height speakers The coded objects, rendered to the floor layout, or virtualised if that mode is chosen No physical overhead placement
TrueHD decoder without Atmos The 7.1 or 5.1 presentation authored at encoding Object metadata is unused; every sound remains in the channel mix
Stereo The stereo downmix of that compatible presentation Surround and height placement are folded into two channels

Using the compatible presentation is the format's designed legacy path, not a damaged decode: Dolby describes an Atmos-capable TrueHD decoder as reversing those downmixes to recover the coded objects.12 Some playback chains ignore the object metadata, for example a decoder without Atmos support or a receiver in a non-Atmos sound mode. The sounds are still heard; they do not come from the positions an Atmos render would give them. Whether a particular receiver does this depends on its model, sound mode and speaker configuration (Denon example below).

Atmos carries spatial information beyond a conventional channel presentation. A renderer maps it to the speaker arrangement. Separate the processing stage from the transport used to reach the receiver:

Processing path What it means
Encoded TrueHD/Atmos passed to the receiver The receiver decodes and renders the disc's coded presentation
Decoded audio with Atmos metadata The source decodes the audio; spatial information remains available for downstream rendering
Audio rendered locally to a selected layout The player has already mapped the source objects to speaker positions; this does not establish preservation of the original dynamic objects downstream
Conventional multichannel PCM A channel presentation such as 7.1; this alone does not establish object rendering or discrete height delivery

Dolby MAT is a transport, not a rendering stage. Dolby describes MAT packing TrueHD for HDMI, and MAT 2.0 carrying PCM with Atmos metadata.1 Local rendering and subsequent MAT packaging can coexist. Do not infer the complete processing history from an “Atmos”, “PCM” or “MAT” label. See Apple TV paths.

Here, “original objects” means the representation encoded on the disc, not an uncompressed studio mix. Testing should distinguish source-object preservation, rendering accuracy and preservation of samples during transport.

DTS-HD Master Audio

DTS-HD Master Audio is lossless audio coding: a compatible decoder reconstructs its coded channel presentation without compression loss. It is distinct from the lossy DTS core and from the additional spatial information in DTS:X. A player may decode it to PCM or bitstream it to a compatible receiver. Subsequent mixing, resampling and processing are separate questions.14

DTS:X

In short: DTS:X is DTS's counterpart to Atmos. It adds height and object information to a lossless DTS-HD Master Audio track, so a DTS:X receiver can place sounds around and above you. DTS describes it as adapting to the speaker layout in the room rather than requiring one fixed arrangement.11 A receiver without DTS:X plays the DTS-HD Master Audio part of the same track.

Decoding the DTS core or DTS-HD MA channel presentation is not the same as using DTS:X spatial extensions. Native Player and AetherEngine describe specific height/rendering paths; those claims should not be generalised to identity with every DTS:X renderer.2

DTS:X likewise supports channel and object-based coding with backward compatibility for DTS-HD decoders. A compatible channel presentation preserves the listening programme without providing the same spatial placement; the lossy DTS core and lossless DTS-HD MA presentation are distinct fallbacks.14

As with Atmos, a decoder without DTS:X still plays the whole soundtrack. One developer describes the common disc layout as a 7.1 DTS-HD MA presentation with the four height channels folded into the floor speakers beneath them, so the height content is heard from the floor.13 That is a developer's description of the tracks it tested, not a DTS specification.

PCM, bitstream and 2.1

Correctly decoded PCM is not inherently inferior to sending a compressed lossless bitstream. If decoding, channel selection, rendering/downmix, gain and processing agree, the resulting samples can agree too.

But “no height speakers” does not guarantee that every setup is bit-identical. Spatial rendering can affect horizontal layouts, and decoders or receivers may apply different downmix coefficients, dialogue normalisation, DRC, resampling or bass management. Do not promise a bitstream benefit—or perfect equality—without defining the comparison.

Stereo does not require rendering height speakers first. Decoding the compatible TrueHD channel presentation and using its supported stereo downmix is a documented legacy playback path. This is channel downmixing, not sample-rate downsampling. It does not simply delete sounds because they were authored as objects. Spatial placement, balance and processing can nevertheless differ from an Atmos render.8

Do not generalise that a Denon receiver always discards object metadata when height speakers are absent. Its selected sound mode and speaker configuration matter: the AVR-X1700H manual documents Atmos rendering and speaker virtualisation without overhead speakers. This does not establish the internal path or sample identity of every Denon model in Stereo mode.

The LFE channel and bass sent to a subwoofer are different. A “2.1” system may be stereo plus bass derived by a crossover, rather than an explicitly transported LFE channel. Compare before bass management and at the final outputs, with gain and timing aligned.

Height channels

Hearing sound from a height speaker does not prove original-object preservation. It might come from object rendering, a fixed rendered bed or an upmixer. Use controlled source signals and disable unrelated enhancement modes when testing.

Spatial fidelity: are sounds in the right place?

In short: lossless decoding recovers the coded audio presentation without compression loss. Subsequent rendering and processing can change the samples. It does not mean every sound comes from the right place. Where a sound ends up is decided by the renderer, which turns objects and their positions into speaker feeds, and by the speakers themselves: their number, placement, levels and distances.

Two systems can therefore receive the same lossless track and still place sounds differently. With bitstream output, the receiver's own Dolby Atmos or DTS:X renderer does the work, set up for the exact speakers it has been configured with. When a player renders locally, as an Apple TV app must to keep height information (why), the player's renderer decides, and the receiver only plays finished speaker channels.

Native Player renders on the Apple TV. Its developer says the rendering follows ETSI TS 103 448, a published specification for turning audio objects into speaker feeds, and that the output nearly matches it. That specification was written for AC-4, Dolby's broadcast and streaming codec, and it can be read by anyone; we have not found a published specification of the renderer a receiver uses for Atmos in TrueHD. The developer says the object metadata it reads is the same format TrueHD Atmos carries, that it is the only object renderer with a public specification, and that apps cannot use the Dolby renderer built into tvOS for TrueHD.5

Where the results can differ, according to the developer: with app and receiver both set to the same layout, such as 7.1.4, the speaker count, the lossless source and the object positions are the same. The receiver also knows which kind of height speakers are installed (front height, top front or top middle), uses extra information such as object size and zones, and renders for the exact setup; the app renders to the standard's nominal speaker positions. The developer's assessment is that this is hard to tell apart for most material. Distances, levels and room correction in the receiver apply either way.5

Height speaker positions. TS 103 448 selects one of a fixed set of layouts and gives each speaker one fixed position: 5.1.4 and 7.1.4 assume top front and top back speakers, 5.1.2 and 7.1.2 top middle speakers. It has no setting for other height positions, such as front height, which a receiver lets you choose. A renderer that follows the specification therefore renders to those positions, whatever is installed. Offering such a setting would mean departing from the specification. That is possible in principle, but Native Player does not offer it at the time of writing.6 So the developer's choice is a documented, public method, but whether it places every object where a receiver's renderer would has not been compared independently.

How to check placement. Use test signals that play from known positions: channel identification for every speaker, including heights, and sounds that move along known paths. Native IT, the maker of Native Player, publishes Sound test for Dolby Atmos for iPhone, iPad and Apple TV, with channel tones and spatial placement tests (more). More test files are wanted.

Films and scenes to try

These community lists are useful for choosing listening material, not proving renderer accuracy:

Verify the disc edition, language track, codec and cut before using a timestamp. Streaming and UHD disc tracks may differ, and a scene list may mix Atmos with DTS:X or conventional surround. Heavy overhead use is a mixing choice, not a measure of quality. Disable upmixing when checking native spatial playback.

HDMI and eARC

Direct HDMI to a compatible receiver reduces the number of intermediaries. If the sound goes through the TV, the TV's connection sets the limit: ARC can carry stereo PCM, but not multichannel PCM or the high-bandwidth lossless bitstreams discussed here, so lossless TrueHD Atmos and DTS:X need eARC on both the TV and the receiver or soundbar, and eARC may have to be switched on in the TV's menu.4 A TV with only ARC cannot pass a disc's lossless Atmos; with such a TV, or with the TV's own speakers, most of the format questions on this page make little difference. If routing through a TV and eARC, verify that the TV passes the actual format. A port label alone is not a format guarantee. The HDMI eARC capability summary lists multichannel PCM and formats including TrueHD and DTS:X; that does not certify a particular TV’s passthrough implementation (S40).

On a disc player, check secondary-audio mixing. Dolby warns that this mode can produce channel-based output instead of the Atmos bitstream.1 Menu names and defaults vary by model.

What matters most

The formats on this page matter, but they are rarely the biggest factor in the sound you hear. Roughly in order of how much they usually matter (an editorial judgement, not a measured ranking):

  • The speakers. Real, separate speakers usually change more than any format detail. Larger speakers and enough amplifier power play louder and cleaner, especially in the bass. A soundbar creates height either by bouncing sound off the ceiling or by virtualisation, which uses filters to make listener-level speakers sound as if they were above you;3 on such a system, adding real speakers, or real height speakers, will usually gain more than work on Atmos transport.
  • The room. Its size, shape, furnishings and reflections shape what reaches your ears; the same speakers can sound quite different in two rooms.
  • Placement and calibration. Where the speakers stand, and setting their levels and distances and integrating the subwoofer, so the channels arrive balanced and on time.7
  • The format and the player. Lossless versus lossy, PCM versus bitstream, and whether objects are rendered correctly (spatial fidelity) come after the above.

Troubleshooting order

Get the system right before comparing transport labels

First: the system itself (what matters most). Resolve missing channels, distortion and unintended stereo downmixing, and check speaker placement, channel routing, levels, delays and subwoofer integration before comparing codecs.7

Then: verify the intended track and playback path. For a height-speaker system, establish whether the original spatial information is actually rendered or passed through, and whether sounds come from the right places (spatial fidelity). Check unintended lossy transcoding or dynamics processing; a format logo alone is insufficient.

Finally: compare lossless PCM and bitstream only with rendering, level and processing controlled. PCM is not inherently a downgrade. On a 2.1 system, correct downmixing and bass management deserve attention before original-object transport; the two paths are not automatically identical.

This is an editorial troubleshooting order, not a universal audibility ranking. The room, speaker layout, source and actual fault determine what matters most. PCM and 2.1 · Controlled listening tests.

Compare player audio paths · Apple TV apps · Measurement protocol

Reviewed 6 November 2026 · Source-reviewed · no local playback measurements

Evidence policy · Sources

  1. S23, Dolby Atmos for sound bar applications, June 2018, pp. 9–11: secondary-audio mixing, TrueHD and MAT. PRIMARY for the format description, not validation of a current app. ↩↩↩

  2. Native Player developer statement; AetherEngine README. ↩

  3. S23, Dolby Atmos for sound bar applications, June 2018, pp. 5–6: two approaches to height in soundbars, upward-firing elements and height virtualisation ("height-cue filters" mixed into listener-level speakers). MANUFACTURER. That real speakers usually matter more is this guide's editorial judgement, not a measured ranking. ↩

  4. Sony ARC documentation explicitly supports two-channel Linear PCM. S40, HDMI Licensing Administrator, Enhanced Audio Return Channel (eARC) (published in Tom's Hardware, May 2021): "eARC can pass uncompressed and higher bandwidth audio; ARC can't"; eARC may need enabling in the TV's settings. Read 8 November 2026. Does not certify any TV's passthrough. ↩

  5. Matrix note 28: Native Player developer's replies, 7 and 8 November 2026 (S52), and ETSI TS 103 448 V1.1.1, AC-4 Object Audio Renderer for Consumer Use, clause 1 (scope). Developer statement; no independent comparison with a receiver's render is known. ↩↩

  6. ETSI TS 103 448 V1.1.1, table 3 (output_speaker_config, a choice of the layouts in table A.1) and Annex A, tables A.5–A.8 (speaker positions per ITU-R BS.2051). PRIMARY; read 8 November 2026. That Native Player renders to these nominal positions is the developer's statement (note 28). ↩

  7. Dolby Atmos Speaker Setup 101 and home installation guidelines, placement, levels and distance calibration. Manufacturer guidance; read 6 November 2026. Does not establish a numerical ranking of audible losses. ↩↩

  8. Dolby Atmos Renderer v3.0 guide, Appendix G, PDF page 265 (zero-based 264), describes backward-compatible TrueHD renders/downmixes. Dolby TrueHD also describes downmixing and independently authored stereo presentations. PRIMARY; checked 6 November 2026. Format behaviour does not prove a particular app/receiver's implementation. ↩

  9. Dolby TrueHD, Dolby Professional. MANUFACTURER format description; checked 6 November 2026. The ZIP comparison is this guide's illustration. ↩

  10. Dolby Atmos, Dolby's consumer introduction; Dolby Atmos for sound bar applications, p. 3 (renderer) and pp. 10–11 (TrueHD and MAT). MANUFACTURER / PRIMARY; checked 6 November 2026. ↩

  11. Welcome to DTS:X, DTS announcement (also published by Xperi), 9 April 2015: “object-based” audio “not tied to prescribed speaker configurations”, with “backward compatibility with existing DTS bitstreams”. MANUFACTURER; launch-era description. dts.com refused automated access on 6 November 2026; the Xperi copy was read. ↩

  12. S49, Dolby Atmos Renderer v3.0 guide, §24.3 “Spatial coding”, PDF pp. 264–266: 9.1 bed plus up to 118 objects grouped into 12, 14 or 16 elements; beds converted to objects; TrueHD carries the coded objects, a 7.1 render and 5.1/stereo downmixes, which an Atmos decoder reverses. PRIMARY (2018 authoring guide); not a test of any player or receiver. ↩↩

  13. S49, AetherEngine docs/formats.md, “DTS:X with heights”, commit f7bea86. DEVELOPER description of twelve tested DTS:X tracks. ↩

  14. DTS production tools and DTS:X introduction. MANUFACTURER format descriptions; checked 6 November 2026. ↩↩

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