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. Compare bitstream and PCM so that you can achieve the best audio output from your Blu-ray Disc player.

Overall Findings

  • The receiver decodes the audio.

  • Potential for higher quality audio.

  • Limited secondary audio quality.

  • 5.1 support over digital optical or coaxial.

  • 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 (the recommended method), there are two main audio output settings: Bitstream and PCM (also called LPCM). In terms of sound quality, whether you set the Blu-ray Disc player's HDMI audio output to PCM or bitstream doesn't matter. However, here is what happens when you choose either setting.

Blu-ray showing Bitstream vs. PCM

The information here focuses on bitstream vs. PCM with regards to Blu-ray Disc players, but it also applies to Ultra HD Blu-ray Disc players.

Signal Decoding

  • The home receiver decodes the audio, expanding quality options.

  • Higher quality sound is possible if the receiver supports it.

  • Transmits standard 5.1 surround signal to receiver.

  • The Blu-ray player decodes the signal, providing quick transfer.

  • Eliminates lag time.

For digital optical and coaxial connections, the bitstream output option can send a standard Dolby Digital or DTS 5.1 surround sound signal to a receiver for decoding, and the PCM option sends only 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.

If you set the Blu-ray Disc player to output audio as PCM, the player performs the audio decoding of all Dolby or Dolby TrueHD and DTS or DTS-HD Master Audio 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 doesn't perform additional audio decoding before the audio is sent through the amplifier section and the speakers.

Receiver Quality Importance

  • Overall, a higher-quality receiver is recommended.

  • The receiver does most of the work.

  • Bitstream is a better choice for digital or coaxial outputs when HDMI isn't available.

  • Demands less of the receiver.

  • Better quality on secondary audio tracks.

Use PCM if you plan to use the secondary audio feature, which provides access to audio commentaries, descriptive audio, and supplementary audio tracks. 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.

Suppose you select bitstream as the HDMI audio output setting for a Blu-ray player. In that case, 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 depending on the type of bitstream signal that 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. No Blu-ray Disc players can decode these formats internally to PCM and pass that 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

Several factors should go into your choice, including the quality of the Blu-ray player and audio receiver. More often than not, you'll want bitstream. The potential for better 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.

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