PCM 5.1 and Surround Sound: Requirements and Compatibility

Can PCM audio be 5.1?

Yes. PCM (pulse-code modulation) is simply uncompressed digital audio, and it can hold any number of channels, including the six channels of a 5.1 surround mix. Whether you actually hear 5.1 PCM depends on the whole chain: the source must contain six channels, the playback device must output multichannel PCM, the cable or link must carry it, and the receiver or soundbar must accept it. In practice, HDMI and HDMI eARC can carry multichannel PCM, while optical (TOSLINK), coaxial S/PDIF and standard HDMI ARC are limited to two-channel PCM. Over those links, surround sound has to travel as a compressed bitstream such as Dolby Digital or DTS instead.

How multichannel PCM works

A PCM signal is a series of samples taken at a fixed sample rate, such as 48 kHz, with a fixed bit depth, such as 16 or 24 bits. In a 5.1 stream, each sample period contains one sample for each of six channels. The PCM format does not apply surround processing itself. It delivers six separate, already-decoded channels to the output device, which routes each one to its speaker.

The six channels of a 5.1 layout are:

• Front left
• Front right
• Center, which carries most dialogue in films and shows
• LFE (low-frequency effects), the ".1" channel sent to the subwoofer
• Surround left
• Surround right

Because PCM is uncompressed, it needs more bandwidth than compressed formats. You can estimate the raw data rate as channels × sample rate × bit depth. Six channels at 48 kHz and 24 bits works out to 6,912,000 bits per second, about 6.9 Mbps. Two-channel S/PDIF connections were not designed for that. HDMI was designed to carry up to eight PCM channels, so it handles this rate easily.

PCM versus bitstream

Surround audio usually reaches your receiver in one of two ways. With bitstream output, the player sends the original encoded track, such as Dolby Digital, DTS or a lossless format, and the receiver decodes it. With PCM output, the player decodes the track itself and sends plain multichannel PCM, so the receiver only needs to play the channels. The receiver's display usually reflects this. It typically shows a PCM or multichannel PCM indicator rather than a Dolby or DTS logo. The exact wording varies by manufacturer and model.

Requirements for 5.1 PCM playback

Check each link in the chain. If any one of them supports only stereo, the result will be stereo, or a downmix of the surround content.

• Source content: the file, disc, stream or game must actually contain a 5.1 (or larger) mix. A stereo track stays stereo even when the output is set to PCM.
• Playback device: the player, console, streaming box or computer must be able to output multichannel PCM, and its audio output setting must allow it. Some devices also offer an automatic mode that decides between PCM and bitstream.
• Connection: use HDMI directly into an AV receiver, or HDMI eARC from a TV to a receiver or soundbar. Optical, coaxial and standard ARC cannot carry 5.1 PCM.
• Receiver or soundbar: it must accept multichannel LPCM on the input you are using. Most AV receivers with HDMI inputs do, but check the documentation for soundbars and older models.
• Speaker configuration: both the playback device and the receiver should be set to a 5.1 speaker layout, and the speakers must be physically connected to match.

Applying this to common setups

Player or console connected to a receiver by HDMI

This setup is the most straightforward. If the device's audio output is set to PCM, it decodes the surround track and sends six channels to the receiver. Choose bitstream instead if you want the receiver to do the decoding, for example to use its own processing modes. If the receiver's display only shows stereo PCM while playing 5.1 content, check the device's audio output and speaker settings first.

TV in the middle of the chain

When a streaming app or a device plugged into the TV sends audio out to a soundbar or receiver, the TV-to-audio link decides what is possible. Over optical or standard ARC, set the TV to pass through or bitstream so that Dolby Digital or DTS 5.1 reaches the audio system. If you choose PCM over these links, you will typically get stereo. Over eARC, multichannel PCM can pass through, provided both the TV and the audio device support eARC and it is enabled on both.

Computer as the source

On a PC, choose the HDMI or multichannel audio interface as the output device in the operating system's sound settings and set its speaker configuration to 5.1 surround. The available options depend on the operating system, the graphics or audio driver and what the connected receiver reports it supports. If 5.1 does not appear as an option, the receiver may not be advertising multichannel support over that connection, or a TV between the PC and the receiver may be limiting the audio format. The player application must also be able to output all six channels instead of downmixing to stereo.

Recording and editing surround audio

Creating your own 5.1 PCM material requires more than a single microphone. Webcams and USB microphones are typically mono or stereo input devices. Recording true surround needs a multichannel audio interface and a microphone arrangement designed for it, or you can mix individual tracks into a 5.1 layout in editing software. When recording, set the input level of each channel so that peaks do not clip. Keep background noise low, because it is more noticeable when spread across surround speakers. Use one sample rate throughout the project to avoid unnecessary resampling. Whether your editor can export multichannel PCM, for example as a six-channel WAV file or a video file with a PCM audio track, depends on the software and its version.

Video calls

Video calling apps typically capture and send mono or stereo audio, so a 5.1 output device does not create surround sound in a call. Incoming call audio may play through the front or center speakers, or the receiver may upmix it, depending on its settings. For calls, choosing the correct microphone and speaker devices and managing background noise matter far more than surround format.

Limits and related questions

Why does optical give me only stereo PCM?

The S/PDIF standard used by optical and coaxial connections carries two channels of uncompressed PCM. Surround sound fits over these links only as compressed Dolby Digital or DTS, which the receiver then decodes. Changing the cable will not change this. You need an HDMI or eARC connection to carry multichannel PCM.

Is PCM surround better than Dolby Digital or DTS?

Not automatically. If the source is a lossy track like Dolby Digital, decoding it to PCM in the player produces the same audio the receiver would have decoded, with no added detail. If the source is lossless, PCM and bitstream output should deliver equivalent sound when both devices decode correctly. The practical differences are which device does the decoding and which processing features stay available.

Does PCM keep Dolby Atmos or DTS:X height information?

Plain channel-based PCM does not carry object-based metadata. When a player converts an Atmos or DTS:X track to ordinary multichannel PCM, the receiver generally receives only the channel mix. Some devices use specific formats designed to carry this information, so check the documentation for your particular player and receiver if height channels matter to you.

Is upmixed stereo the same as 5.1 PCM?

No. Many receivers and soundbars can spread a stereo PCM signal across all speakers with their own processing modes. This can sound surround-like, but the receiver derives those channels from two. Real 5.1 PCM contains six discrete channels created in the original mix.

Quick checks when 5.1 PCM is not working

• Confirm the content itself has a 5.1 track and that the track is selected in the player.
• Check what the receiver's display reports while the content is playing.
• Look for an optical, coaxial or standard ARC link anywhere in the chain.
• Verify that the playback device's speaker configuration is set to 5.1 rather than stereo.
• Make sure the receiver's speaker setup matches the speakers actually connected.
• If a TV sits between the source and the audio system, check its audio output and pass-through settings.