What Bitstream Is and How It Works in Home Theater Audio

Bitstream Audio is a crucial element in home theater audio

A digital bitstream

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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 are almost magic.

One technology used to deliver 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 can be used to convert sound into digital bits and then that information is transferred from a source device to a receiver, and, eventually, to your ears.

PCM and Hi-Res audio are examples of digital audio formats that utilize bitstreams.

How Bitstream Is Used in a Home Theater

In a home theater, 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.

A home theater receiver or AV processor detects an encoded surround format sent to it. The receiver/AV processor proceeds to decode the information based on instructions provided in the bitstream signal. Post-processing may be added and the signal is converted 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 deciding what surround sound format to use for a specific audio recording or live transmission and 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 placed on a Disc (DVD, Blu-ray, Ultra HD Blu-ray), cable or satellite service, streaming source, or 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 bitstream can be sent from the chosen source directly to a home theater receiver (or AV Preamp/Processor) via a physical connection (digital optical, digital coaxial, or HDMI). 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 home theater:

  • A DVD, Blu-ray, or Ultra HD disc contains a Dolby Digital or DTS soundtrack that is encoded as digital bits. The player reads the encoding off of the disc, transfers it 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 decodes the Dolby Digital or DTS bitstream into its proper channel assignments and sends the assigned channel signals through the appropriate amplifiers, and on to the speakers.
  • In addition to the above method, 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. Instead of the receiver decoding the bitstream coming from a player, the player may be able to send a decoded signal in PCM form digitally to a home theater receiver via HDMI or in analog form through multichannel analog audio connections. The receiver's own decoders are bypassed with the audio signal passing directly through the receiver, its amplifiers and on to the speakers without further processing unless the listener activates more in the receiver/AV processor.
  • A TV station transmits a signal that includes a Dolby Digital-encoded bitstream. A TV receives that signal, then transfers the bitstream to a 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. If the media streamer is connected directly to a TV via HDMI, and the TV is connected to a compatible soundbar or home theater receiver via digital audio output or via HDMI Audio Return Channel, the TV will pass the bitstream signal 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.