Blu-ray Disc Player Audio Settings: Bitstream vs. PCM

Accessing Dolby, DTS, and PCM audio streams from a Blu-ray Disc player

The Blu-ray Disc format provides an enhanced viewing experience and elevated surround sound listening. Blu-ray Disc players provide several setting options for audio and video output, depending on how your player is physically connected to your home theater receiver. We compared bitstream and PCM so that you can achieve the best audio output from your Blu-ray Disc player.

Illustration showing Blu-ray showing Bitstream vs. PCM
Lifewire

Overall Findings

Bitstream
  • The receiver decodes the audio.

  • Potential for higher quality audio.

  • Limited secondary audio quality.

  • 5.1 support over digital optical or coaxial.

PCM
  • The Blu-ray player decodes the audio.

  • Requires higher bandwidth.

  • Better for secondary audio channels.

  • Limited digital optical or coaxial output.

For audio, if you connect a Blu-ray Disc player to a home theater receiver via HDMI, there are two main audio output settings available: Bitstream and PCM (which is also called LPCM). In terms of sound quality, whether you set the Blu-ray Disc player's HDMI audio output PCM or bitstream doesn't matter. However, here is what happens when you choose either setting.

Although the below discussion focuses on bitstream vs. PCM with regards to Blu-ray Disc players, the same information can also be applied to Ultra HD Blu-ray Disc players.

PCM Pros and Cons

Advantages
  • Decoding is done in the Blu-ray player.

  • Less work for the receiver.

  • Quicker, direct, and eliminates lag.

  • Better quality access to additional audio tracks.

Disadvantages
  • More work is done by the player.

  • Audio quality is partially determined by the Blu-ray player.

  • PCM transmits a two-channel signal over digital optical or coaxial.

If you set the Blu-ray Disc player to output audio as PCM, the player performs the audio decoding of all Dolby/Dolby TrueHD and DTS/DTS-HD Master Audio related soundtracks internally. Then, it sends the decoded audio signal in an uncompressed form to the home theater receiver. As a result, the home theater receiver won't perform additional audio decoding before the audio is sent through the amplifier section and the speakers. With this option, the home theater receiver displays the term PCM or LPCM on its front panel display.

If you plan to use the secondary audio feature, which provides access to audio commentaries, descriptive audio, and supplementary audio tracks, use PCM. When access to these audio programs is important to you, set the Blu-ray player to PCM to provide the best quality result. The player decodes the audio, without bandwidth concern, which is an issue for bitstream.

For digital optical and coaxial connections, while the bitstream output option can send a standard Dolby Digital or DTS 5.1 surround sound signal to a receiver for decoding, the PCM option sends a two-channel signal. A digital optical or digital coaxial cable doesn't have sufficient bandwidth capacity to transfer a decoded, uncompressed, full surround audio signal like an HDMI connection can.

Bitstream Pros and Cons

Advantages
  • The home receiver decodes audio.

  • If the receiver offers higher quality audio processing, it can be used.

  • Possibility of higher quality sound.

  • Bitstream sends an encoded 5.1 signal over digital optical or coaxial.

Disadvantages
  • More work is placed on the receiver.

  • Requires a high-quality receiver to achieve better results.

  • Supplemental audio is scaled down, which decreases quality.

If you select bitstream as the HDMI audio output setting for a Blu-ray player, the player bypasses its internal Dolby and DTS audio decoders and sends the undecoded signal to your HDMI-connected home theater receiver. The home theater receiver does the audio decoding of the incoming signal. As a result, the receiver will display Dolby, Dolby TrueHD, DTS, DTS-HD Master Audio, Dolby Atmos, DTS:X, or another format on its front panel display depending on which type of bitstream signal is decoded.

The Dolby Atmos and DTS:X surround sound formats are only available from a Blu-ray Disc player via the bitstream setting option. There are no Blu-ray Disc players that can decode these formats internally to PCM and pass that on to a home theater receiver.

If you combine the bitstream and secondary audio settings, the Blu-ray Disc player will down-res surround formats, such as Dolby TrueHD or DTS-HD, to standard Dolby Digital or DTS to squeeze both types of audio signals into the same bitstream bandwidth. In this case, the home theater receiver recognizes the signal as standard Dolby Digital and decodes appropriately.

HDMI is easily the best option for output. However, if you use either digital or optical coaxial outputs, bitstream is the clear winner. Digital optical and coaxial connections suffer from limited bandwidth and can't transfer a fully-processed and decoded signal. Because bitstream relies on the receiver for decoding, it's ideal for limited bandwidth situations.

Final Verdict

There are a number of factors that should go into your choice, including the quality of your Blu-ray player and audio receiver. More often than not, you'll want bitstream. The potential for greater audio quality and the flexibility to use coaxial outputs puts it ahead of PCM.

The only situation where PCM comes out on top is when using secondary audio streams. If you don't plan on doing this, and your receiver isn't severely lacking in quality, go for bitstream.