Bitstream: What It is and How It Works in Home Theater Audio

Bitstream Audio is a crucial element in home theater - find out why

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 (aka Bitstream Audio, Bit Stream, Digital Bitstream, or Audio Bitstream).

Bitstream Defined

A Bitstream is binary bits of information (1's and 0's) that can be 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 of audio that utilize bitstreams to transfer digital audio signals.

How Bitstream Is Used 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 or AV preamp/processor/Power amplifier combination.

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

The bitstream process starts with the 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 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, Atmos, DTS, DTS-ES, DTS 96/24, DTS HD-Master Audio, and DTS:X.

The needed bitstream can be sent from a source directly to a home theater receiver (or AV Preamp/Processor) 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 can work in a home theater setup:

  • A DVD, Blu-ray, or Ultra HD disc contains a Dolby Digital or DTS soundtrack that is encoded as digital bits. A compatible player must read this encoding off of the disc, transfer the encoded signal in bitstream form via digital optical, digital coaxial, or HDMI connection to a Home Theater Receiver/AV Preamp Processor that has a Dolby Digital or DTS Decoder.The receiver, in turn, decodes the Dolby Digital or DTS bitstream into its proper channel assignments and sends the assigned channel signals through the appropriate amplifiers, so that it can be heard by the listener through loudspeakers.
  • In addition to the above method of managing a bitstream, a DVD Blu-ray, or Ultra HD Disc player may also provide the capability to decode the bitstream coming from a disc internally to the PCM format.This means that instead of depending on a receiver to decode a bitstream coming from a player, in some cases you can opt to have the player send an already decoded signal in PCM form digitally to a home theater receiver via HDMI or in analog form through multichannel analog audio connections.
    • In these cases, the receiver's own decoders are bypassed and the audio signal is passed directly through the receiver to its amplifiers and on to the speakers without further processing unless the listener activates any additional processing within the home theater receiver or AV preamp/processor.
  • A TV station transmits a signal over its assigned channel that includes a Dolby Digital-encoded bitstream. A compatible TV receives that signal, then transfers the bitstream to a compatible soundbar, home theater receiver, or av preamp/processor using either a digital optical output or HDMI Audio Return Channel. The soundbar, home theater receiver, or av preamp/processor then decodes the bitstream and plays the decoded signal. Depending on the soundbar, receiver, av preamp/processor, the user may also have the option of combining the decoded Dolby Digital result with additional audio processing.
  • 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, and it is 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 soundbar/home theater for decoding and amplification.
  • In another internet streaming scenario, you might receive Netflix or other services directly through a Smart TV. If so, the TV may be able to pass an encoded Dolby Digital signal to a soundbar, home theater receiver, or av preamp/processor using the same methods as when the TV receives a station broadcast - via digital optical or HDMI Audio Return Channel for decoding and any additional user chosen process for added listening enjoyment.

The Bottom Line

Bitstream encoding is a core technology 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 or AV preamp/processor within a narrow bandwidth using a variety of connection options.