The various surround sound formats available on modern AV receivers can appear confusing.
Dolby Digital, DTS and THX listening modes are all available to process your audio, but what is the difference and what do they all do?
On this page, I list some of the audio decoding and processing formats you will find on your hardware and give a few details as to when you might use them.
You may come across other audio formats in addition to those listed here, but these are the most common and well-used.
You will find that some of the processing modes on your AV receiver are only available for certain types of input - i.e. for analog/PCM stereo inputs or for Dolby Digital/DTS multichannel inputs.
Dolby Digital is the most common surround sound format on DVD and Blu-ray discs. It is also the format used by most streaming and broadcast TV services.
It is sometimes called AC-3.
Any Dolby Digital soundtrack will be decoded automatically by an AV receiver that supports this format - which is pretty much all of them.
The most common type of Dolby Digital is 5.1 surround sound, but there are some Dolby Digital 2.0 soundtracks for systems with stereo speakers rather than surround sound setups.
Dolby Digital can be sent over HDMI or optical/coaxial connections, and the AV receiver will then decode the signal and play it as 5.1 surround sound - or stereo for DD 2.0.
'Dolby Digital' will be displayed on the front panel display, confirming it's receiving and decoding the data stream.
DD is a lossy format, which means the original audio from the film studio is compressed to fit on the disc.
This compression will lose some of the original sound quality, although it still sounds pretty good on a decent sound system.
The maximum audio bandwidth of Dolby Digital 5.1 on a Blu-ray disc is 640 kbps - although encoded bitrates may range from 384-640 kbps.
On DVD, the maximum bitrate for surround sound is 448 kbps.
The bitrate for stereo Dolby Digital will usually be around 192 kbps.
A Dolby Digital EX soundtrack has an extra surround channel.
This allows for an extra
speaker at the rear of the room - thus creating a 6.1 system.
A Dolby Digital EX enabled receiver can decode this type of codec and accommodate the extra surround speaker.
Therefore, 5.1-channel AV receivers won't support Dolby Digital EX as they can't power the extra rear speaker.
If there is no extra surround speaker attached to the receiver, it will simply play the 5.1 soundtrack if you play the Dolby Digital EX version.
There are actually two different variations of Dolby Digital EX - Matrix 6.1 and Discrete 6.1.
Matrix 6.1 creates the extra rear channel from the standard 5.1 soundtrack.
Whereas a Discrete 6.1 soundtrack actually has a dedicated extra channel.
Also known as E-AC-3 (Enhanced AC-3), Dolby Digital Plus can support up to 15-channels of audio and a wider range of data rates than standard AC-3.
It is optional for Blu-ray discs and is most likely used with a 6.1 or 7.1
However, with the lack of 7.1
soundtracks, most studios will provide a DD 5.1 soundtrack on a disc
rather than Dolby Digital+.
Compared to standard Dolby Digital 5.1, DD+ has an increased maximum bandwidth of 1.7 Mbps on Blu-ray.
This means you should hear a better sound quality if you have the sound system to make the most of it.
However, because it supports a wide range of data rates, Dolby Digital Plus has also become a popular audio format for streaming services such as Netflix, Amazon Prime and Disney+.
In this case, typical bitrates might be around 192-256 kbps for 5.1 audio.
Aside from the support for lower data rates, another significant advantage of using DD+ for streaming is that Dolby Atmos' metadata can be embedded with this format.
On Blu-ray, Dolby Atmos is usually only available with high-resolution audio formats.
But DD+ allows streaming services to offer Dolby Atmos sound with a lower bandwidth requirement.
Your AV receiver will need to decode DD+ to play this format - and pretty much all models from the past few years will.
If you want to hear the Dolby Atmos version, your receiver will need to support this too.
Dolby TrueHD is a lossless codec found on HD and UHD Blu-ray discs.
It supports sample rates from 44.1 kHz to 192 kHz and up to 24-bit audio.
This type of audio will be detected automatically by an AV receiver if it has an onboard decoder.
If decoded by the AV receiver, this codec can be sent over HDMI as a bitstream from the Blu-ray player, and the front panel will display 'Dolby TrueHD.'
Older AV receivers may not be able to decode this format. But any recent model will.
If the receiver cannot decode Dolby TrueHD, it can still play this audio type if the Blu-ray player decodes Dolby TrueHD first and then sends it as LPCM.
In this instance, the front panel will display 'Multichannel Audio' (or words to that effect) - but you will still be hearing actual HD audio.
As mentioned previously, Dolby TrueHD's main advantage over standard Dolby Digital is it uses lossless compression to transfer it to a disc.
Although it is still compressed, there is no audio quality loss from the original studio master tapes.
This will result in crisper high frequencies, deeper bass, and a more-defined surround effect on a good sound system.
TrueHD soundtracks are only available on Blu-ray discs - they are too large for DVD discs.
Dolby Atmos metadata can be embedded with Dolby TrueHD to provide a complete 3D audio experience.
Unlike the previous four codecs, which are encoded on the disc, this is a processing format that takes a stereo audio signal and creates a virtual 5.1 surround sound effect.
Therefore it allows those with a 5.1 speaker setup to enjoy surround sound from sources that only provide a stereo signal - such as most TV channels.
It also works on a Dolby Surround 4-channel signal. It's not as good as an actual 5.1 soundtrack, but it can be pretty effective.
There will often be three different versions of Dolby Pro Logic II - Movie, Music and Game. These different types have all been optimized to suit differences in the source audio.
The 'Movie' version is designed for stereo and Dolby Surround movies and TV shows.
The 'Music' version allows the user to adjust the sound stage width for music sources, and the 'Game' version is optimized for video games.
Choose the relevant type depending on what you are listening to.
This is an older processing format more likely found on older receivers.
New AV receivers will probably have Dolby Surround instead - which is explained below.
This is an enhancement of Dolby Pro Logic II.
It converts stereo or 5.1 soundtracks into 6.1 or 7.1 - depending on the speaker setup you have in your room.
This will only be available on receivers that support speaker setups greater than 5.1, and it also comes with Movie, Music and Game versions.
Dolby Pro Logic IIz is an improvement on Dolby Pro Logic IIx.
This version adds a new height dimension to surround sound.
The idea of Dolby Pro Logic IIz is to add two speakers above the usual front left and right speakers to create an even more realistic feel to certain sound effects - especially things like wind and rain.
The height speakers can be added to a 5.1 system to create 7.1 (with front height speakers instead of back left and right) or a 7.1 system to create a 9.1 system.
Obviously, the AV receiver will need to support these speaker configurations for this to be available.
This is a relatively new codec developed by Dolby, initially for use in the cinema.
However, starting in 2014, some Blu-ray disc releases started to appear with a Dolby Atmos soundtrack. They are now more common on new releases, although not universal.
Dolby Atmos is the first codec released that was object-based - which means that a sound object can be placed in a more precise position in the sound-field and is not tied to a particular channel.
The simplest Dolby Atmos speaker setup requires an extra pair of front speakers that are raised much higher than those in a traditional 5.1 system. This allows the listener to experience sound that moves up and down - as well as left to right.
This speaker setup, with two extra height speakers, is known as a 5.1.2 system. The height speakers are denoted by the extra .2 on the end.
The height speakers can be ceiling mounted speakers or Dolby Atmos-enabled speakers which fire the sound upwards.
If a 5.1.2 speaker system isn't enough for you, the speaker layout limit of Dolby Atmos is 24.1.10.
So, 34 surround sound speakers plus a subwoofer. Now, that would be quite some speaker system in your front room!
This is an optional format, and you will currently only be able to play the Dolby Atmos soundtrack on your disc if your AV receiver supports it.
Any Blu-ray player with a minimum HDMI 1.4 specification will be able to bitstream this to the receiver.
Dolby Atmos is layered as metadata on top of a Dolby TrueHD soundtrack. So, as long as your hardware supports TrueHD then you should be fine.
Remember, your AV receiver will need to support height speakers to play this format.
Most AV receiver manufacturers are now releasing some models in their range that supports the decoding of Dolby Atmos. In fact, even the cheaper AV receivers under $500 will often have this capability built-in.
While Dolby Atmos soundtracks are often thought to be limited to only systems that support high-resolution audio formats, this is not the case.
Dolby updated the specification to allow Dolby Atmos to be embedded with a Dolby Digital Plus soundtrack.
This is how you get Dolby Atmos sound from a streaming service like Netflix and Disney+.
So, Dolby Atmos sounds excellent, doesn't it?
However, there aren't that many Dolby Atmos soundtracks available on the discs we buy. So, what happens to our lovely height/elevation speakers when we play a standard 5.1 or 7.1 mix?
This is where Dolby Surround comes in.
Dolby Surround is an upmixing algorithm. It will take a standard surround mix and create the extra channels that your system supports.
So, if you have two (or more) height speakers installed on your AV receiver, then Dolby Surround will create channels for them from a 5.1/7.1 soundtrack.
In fact, it can also do this from a simple stereo track.
It will work on surround systems with extra surround, height, ceiling or up-firing speakers. Or, upmix stereo into 5.1 if that is what you have installed.
If you think this sounds remarkably like Dolby Pro Logic IIx/z discussed above - then you would be right.
Dolby Surround is just the more modern version and is much more advanced. It can recreate the placement of individual sound effects as well as height information.
This is the version you will likely find on a new AV receiver.
Not all AV receivers will come with this mode. So, check the specifications if you want this before you buy.
Also, depending on the model of receiver that you have, you may find that Dolby Surround is limited to certain types of soundtrack.
The newer 3D audio technologies like Dolby Atmos are all very well, but they do require a bit of space in your room to install the extra speakers.
If you like the idea of experiencing this 360° audio effect, but don't have space - or money - for more speakers, then this sound processing feature is for you.
Dolby Atmos Height Virtualization Technology creates the effect of a Dolby Atmos soundtrack - but without the need for height speakers.
As long as your AV receiver has this option, Dolby Atmos Height Virtualization can be enabled with any speaker layout that doesn't have overhead or Dolby Atmos-enabled elevation speakers. From a simple stereo setup - to 5.1 and 7.1 surround sound systems.
Obviously, if you do have elevation or height speakers, you don't need to use this format.
This technology adds filters to the soundtrack that will simulate sounds coming from overhead. So, you can have some of the fun of Dolby Atmos without the extra cost of more speakers.
In my experience, it's not as effective as with actual height speakers in the room, but it can give an interesting extra sense of space that isn't there otherwise.
If you have an AV receiver with this technology installed, give it a go and see if you like it. You can always turn it off again.
Dolby Atmos Height Virtualization is similar to DTS Virtual:X, which has been around for a while.
This format will be detected and decoded automatically by an AV receiver with a DTS decoder.
Therefore, if you play a DTS soundtrack on a Blu-ray or DVD, the receiver will accept the signal over HDMI or coaxial/optical connections, display 'DTS' or 'DTS 5.1', and send the audio to the 5.1 speaker system.
Like Dolby Digital, this is a lossy format, so the compression onto the disc will lose some of the original sound quality from the studio master.
But, at 1.5 Mbps, DTS supports a higher bit rate than DD. Because of this, many people say the sound of DTS is slightly better than the Dolby version.
However, this assumes that the audio encoding uses the extra available bandwidth (which is not guaranteed) - and the average home user will probably not notice the difference anyway.
This format takes a stereo sound source and creates virtual surround sound - either 5.1 or 6.1, depending on your hardware setup. In this respect, it does a similar thing to Dolby Pro Logic II and IIx.
However, there are differences in the resulting sound between the two systems, and so it is advisable to try both and see if you prefer one over the other.
DTS Neo:6 comes in two versions - Cinema and Music. These are optimized for different types of audio - movies/TV shows and music. Switch the mode depending on the type of audio you are listening to.
It can also create a 6.1 surround mix (with the additional center surround speaker) from a 5.1 soundtrack.
This will be available on some AV receivers for decoding DTS-ES soundtracks.
These versions are an extension of DTS 5.1 with an extra surround channel encoded in the standard left and right surround channels.
The extra channel will only play on an AV receiver with the additional speaker installed to create a 6.1 system.
An AV receiver that can decode this type of audio on-board will automatically switch to this setting when detecting the incoming signal over HDMI.
It will then play the multichannel audio according to the encoded data on the disc and display 'DTS-HS Master Audio' on the front panel display.
As already mentioned with Dolby TrueHD, some AV receivers cannot decode HD audio.
In this case, you will need a Blu-ray player that can decode DTS-HD Master Audio on-board.
You can then set the Blu-ray player to send the decoded audio to the AV receiver. This can be as LPCM over HDMI or via its own multichannel analog outputs.
If you send the decoded LPCM, the front panel display will read 'Multichannel Audio' as it receives LPCM rather than the original Master Audio data stream.
Like Dolby TrueHD, DTS-HD Master Audio uses lossless compression. Therefore, it will sound as sharp and clear as the original studio soundtrack.
As they are both lossless audio, there shouldn't be any audio quality difference between DTS-HD Master Audio and Dolby True-HD.
DTS-HD Master Audio is only available on Blu-ray discs as the data is too large to fit on a DVD.
A new innovation in surround sound audio is object-based audio soundtracks.
Started by Dolby Atmos, DTS:X is the object-based equivalent from DTS Audio.
It allows the listener to experience the audio in a more 3D fashion - with height information as well as left/right and front/back.
Your AV receiver must support the decoding of DTS:X for you to enjoy this new type of audio experience.
The main difference from Dolby Atmos is that you can experience DTS:X using a conventional 5.1 or 7.1 speaker system. You don't need to add extra height speakers as with Dolby Atmos.
Having said that, a DTS:X AV receiver that will support extra speaker channels will get you a greater 3D experience if you have more speakers - especially height speakers.
Due to licensing and processing power limits, DTS:X is will only support speaker layouts up to 11.1 speakers.
As with Dolby Atmos, the bitstreaming of a DTS:X soundtrack is supported by any Blu-ray player with a minimum of HDMI 1.4 specification, so older players are supported.
DTS:X is layered on top of a DTS-HD Master Audio soundtrack, and most modern players and receivers will support this.
The important thing is that your AV receiver can decode DTS:X when it receives the information from your Blu-ray player.
Check out the article the best AV receivers in 2021 to find an AV receiver that supports DTS:X.
This is the DTS equivalent to Dolby Surround.
So, if you have height or up-firing speakers connected to your AV receiver, then you can enable this on stereo or standard multichannel soundtracks.
Neural:X will then create extra pseudo channels to make full use of all the speakers in your room.
Neural:X won't be available on all AV receivers, so make sure you check this before you buy.
You might also find that some AV receivers won't allow you to use this on certain types of soundtracks.
For example, in the early days, many models wouldn't allow this to be selected on Dolby soundtracks.
However, that has changed recently. Still, it's something you should check if you think you might be using it.
A new addition to the DTS audio format family is DTS:X Pro.
This new processing mode will work on all soundtracks on your Blu-ray/ DVD discs - like DTS 5.1 and DTS:X.
If your AV receiver supports this processing mode, you will increase the 11.1 speaker limit of DTS:X.
This is because DTS:X Pro supports speaker layouts up to 30.2 speakers.
You will need a very advanced AV processor to get to this amount of speakers. However, there are one or two integrated AV receivers that have 13-channels of amplification.
If you have one of these, you will be able to upmix any DTS soundtrack across your complete speaker system.
It will use the DTS Neural:X algorithm to upmix standard channel-based soundtracks.
Plus, DTS:X Pro will also decode and render an object-based DTS:X soundtrack across all your speakers.
Unlike DTS:X, this is not a soundtrack type that can be found on your Blu-ray disc. It’s a digital processing mode which can be used on a few different kinds of audio.
Not all AV receivers will support it. So, check before you buy if it’s something you want.
The aim of DTS Virtual:X is to give you the 3D experience of an object-based soundtrack – but without you having to install any height speakers. So, this can be great if you haven’t got the space – or money – for the extra hardware.
Therefore, DTS Virtual:X will work on any speaker configuration that doesn’t have any height speakers. So, 2.1, 3.1, 5.1 – even a simple soundbar setup.
You should be able to select this format on your receiver for any type of DTS soundtrack – or any PCM or multichannel PCM signal. Stereo or surround.
The only thing to be aware of is that you won’t be able to use it if you are playing any Dolby-encoded material. Dolby prevents this in their licensing agreement.
DTS Virtual:X won’t sound as effective as having actual height speakers with a proper object-based soundtrack. But it can be effective in giving an extra sense of space.
It can also help to make the dialogue clearer.
Here’s a video from DTS that shows a bit more about it:
Some AV receiver models (often the more expensive ones!) are THX certified and may offer extra THX listening modes.
THX certification means that a product meets certain standards defined by THX, who aim to set the highest standards for home theater video and audio equipment.
This certification isn't limited to AV receivers, and we can find THX-certified products across all types of audio-visual hardware.
While we should never assume that a product without THX certification must be of poor quality, we should be confident of a high-quality product where we find this mark of approval.
A THX-certified receiver will have THX Surround Sound Modes, which use a technology called THX Advanced Speaker Array (THX ASA).
The three listening modes - Cinema, Games and Music - are similar to Pro Logic in that they can play any type of source material and match it to the speaker setup you have in your room.
The difference with the THX listening modes is they also add equalization to the audio to tailor the original soundtrack mix to suit a home environment.
The theory is that movie soundtracks are mixed to sound good at high volumes in movie theaters but will sound different at lower volumes in regular rooms.
Therefore, these modes are designed to alter the frequency response of the sound you hear and allow for the differences between an actual movie theater and your room.
If you have these listening modes on your equipment, you may find that you can improve the sound in your room by activating these settings. Give it a try and see what you think.
They can be used on their own or alongside the various Dolby and DTS modes listed above.
IMAX Enhanced is a new content and hardware standard released by IMAX.
The aim is to provide the best image and audio quality currently available through a combination of new content and certified hardware.
While not precisely a surround sound format as such, I thought it would be helpful to mention it here as you may well come across it as an audio format and wonder what it is.
Image content is optimized for large 4K HDR displays with a new mastering process so that you get an exceptionally bright and colorful image.
The audio is mixed with a special version of DTS:X, designed for surround sound systems with elevation or height speakers.
The minimum required speaker layout is 5.1.4. Although the recommended system is 7.2.4.
Having said that, the algorithm will adapt to systems with different speaker layouts than those mentioned. So you will be able to use it regardless of your speaker layout.
To experience IMAX Enhanced to the full, you will need two things:
Some new TVs are now being released with the IMAX Enhanced badge. While AV receivers and processors are also starting to appear with the technology built-in.
You can still benefit from IMAX Enhanced content if you don't have certified hardware. But, you will get the best experience if all your hardware is IMAX Enhanced compliant.
As for the content, you should see more appearing as time goes on. You will be able to find IMAX Enhanced movies on 4K UHD Blu-ray discs. Plus, the technology can be streamed, so keep a lookout at a streaming service near you!
This video gives a brief introduction to the technology:
The types of decoding/processing listed above are the most common versions that we will find on many AV receivers.
However, each manufacturer will often provide additional DSP (Digital Signal Processing) listening modes for you to choose from.
These different versions will provide other processing options to alter the sound that you hear through your system.
Such processing modes can include:
Feel free to play with these and see if you like the resulting sound.
Follow the link if you want to learn a little more about listening modes in AV receivers.
As you can see, the surround sound formats and listening modes that AV receivers have can seem quite complex.
However, the idea is to give you the flexibility to tweak the audio you hear to suit your room and hardware setup.
There is no way a movie can be made to sound the same in all types of room - and with different speaker configurations.
So, at least we have the option of adjusting the audio slightly to suit our hardware and taste.
Fortunately, some options will be selected automatically by your hardware, depending on the type of audio you are playing.
But it can help you understand the options you have for changing the settings because it can allow you to get an even better sound in your room.
To understand how these surround sound formats fit into the bigger picture you may want to check my guide to Blu-ray audio formats.
Paul started the Home Cinema Guide to help less-experienced users get the most out of today's audio-visual technology. He has worked as a sound, lighting and audio-visual engineer for around 20 years. At home, he has spent more time than is probably healthy installing, configuring, testing, de-rigging, fixing, tweaking, re-installing again (and sometimes using) various pieces of hi-fi and home cinema equipment.