What Does Bitstream Mean in a Home Theater System?

A digital bitstream
A digital bitstream. Sebastian Kaulitzki/Getty Images

We take the ease at which we listen to audio for granted, but getting music, dialogue, and sound effects from a source to your ears requires technologies that almost seem like magic.

One technology that is employed in delivering sound is referred to as a Bitstream.

The bitstream may also be referred to as Bit Stream, Digital Bitstream, or Audio Bitstream.

Bitstream Defined

A Bitstream refers to binary bits of information (1's and 0's) transferred from one device to another.

Bitstreams are used in PC, networking, and audio applications.

For audio, a bitstream involves converting sound into digital bits of information (1's and 0's) and then transferring that information from a source device to a receiver, and, eventually, to your ears.

For example, PCM and Hi-Res audio are examples in audio that utilize bitstreams to transfer digital audio signals.

How Bitstream Is Applied In Home Theater

In home theater applications, a bitstream is more narrowly defined as a method of transferring encoded audio signals of specific surround sound formats from a source to a compatible home theater receiver.

The home theater receiver detects what encoded surround format is being received. The receiver then proceeds to decode the information based on the instructions provided in the in the bitstream signal, adds any additional processing, and finally converts it analog form so that it can be amplified and sent to the speakers so you can hear it.

The bitstream process starts with content creator and/or sound engineer/mixer. In order for bitstream to work, the content creator/sound engineer first decides what surround sound format to use for a specific analog audio recording or live transmission. The creator (sound engineer, mixer) then proceeds to encode the audio as digital bits in the format chosen according to the rules of the format.

Once that process is completed, the bits are then placed on a Disc (DVD, Blu-ray, Ultra HD Blu-ray), cable or satellite service, streaming source, or even embedded in a live TV transmission.

Examples of surround sound formats that utilize the bitstream transfer process include Dolby Digital, EX, Plus, TrueHD, AtmosDTS, DTS-ES, DTS 96/24, DTS HD-Master Audio, and DTS:X.

The bitstream can be sent from a source directly to a home theater receiver (or AV Preamp/Processor - Power Amplifier combination) via a physical connection (digital optical, digital coaxial, or HDMI interface) from the appropriate disc player, media streamer, or cable/satellite box. A bitstream can also be sent wirelessly via antenna or home network.

Examples of Bitstream Management

Here are examples of how bitstream audio transfer might work in a home theater setup:

  • A DVD, Blu-ray, or Ultra HD disc player "X" contains a Dolby Digital or DTS soundtrack that is encoded as digital bits on the disc. The DVD player must read this encoding, transfer the encoded signal in bitstream form via digital optical, digital coaxial, or HDMI connection to a Home Theater Receiver "Y" that has a Dolby Digital or DTS Decoder. The receiver, in turn, converts the digitally encoded Dolby Digital or DTS bitstream into the proper channel assignment in an analog form, then amplified, so that it can be heard by the listener through Loudspeakers.
  • In addition to the above method of managing a bitstream, a DVD or Blu-ray Disc player may also provide the capability to decode the bitstream internally to the PCM format, instead of depending on the receiver to perform this task. In this situation, the DVD or Blu-ray Disc player transfers the PCM signal to a home theater receiver via HDMI or multichannel analog audio connections. In this case, the receiver's own decoders are bypassed and the audio signal is passed directly through the amplifiers and on to the speakers.
  • A TV channel transmits a signal that includes a Dolby Digital-encoded bitstream. A compatible TV receives that signal, then transfers the bitstream to a compatible sound bar or home theater receiver using either a digital optical output or HDMI Audio Return Channel. The sound bar or home theater receiver then decodes the bitstream and plays the decoded signal.
  • For internet streaming, a service, such as Netflix, offers a program or movie encoded in Dolby Digital or related surround sound format. If you receive that content using a media streamer, if it connected to a home theater receiver using a digital audio connection (optical, coaxial, HDMI), the surround sound audio bitstream is sent to the receiver, decoded, and sent through the amplifier and speakers. Likewise, if the media streamer is connected directly to a TV via HDMI, and the TV is connected to a compatible sound bar or home theater receiver via digital audio output or via HDMI Audio Return Channel, the TV will pass the bitstream signal through the TV and out to the sound bar/home theater for decoding and amplification.

The Bottom Line

Bitstream encoding is a core tool that is used in home theater audio. It provides a way to transfer data- heavy surround sound information between a source device and a home theater receiver within a narrow bandwidth using a variety of connection options, depending on the capabilities of the components used.

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