What Is Bitstream and How Does It Work?

It's easy to listen to music these days. But the process of getting music, dialogue, and sound effects from a source to your ears is a complicated process involving seemingly magical technologies.

One technology used to deliver sound is a Bitstream (aka Bitstream Audio, Bit Stream, Digital Bitstream, or Audio Bitstream).

What Is Bitstream?

A bitstream is binary bits of information (1s and 0s) that can transfer from one device to another. Bitstreams are used in computer, networking, and audio applications.

For audio, a bitstream can 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 Does Bitstream Work?

A bitstream is 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 in a home theater.

A home theater receiver or AV processor detects the encoded surround format sent to it. The receiver/AV processor then decodes the information based on instructions provided in the bitstream signal. Post-processing and converting the signal to analog form amplifies and sends the audio to the speakers.

The bitstream process starts with the content creator or sound engineer deciding what surround sound format to use for an audio recording or live transmission. The audio is then encoded as digital bits in the chosen format and according to the format's rules.

Once that process is complete, the bits go to a disc (DVD, Blu-ray, or Ultra HD Blu-ray), cable or satellite service, streaming source, or embedded in 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 an 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 encoded as digital bits. The player reads the disc's encoding, transfers it in bitstream form via a 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 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 from a disc internally to the PCM format. Instead of the receiver decoding the bitstream coming from a player, the player may send a decoded signal in the PCM format digitally to a home theater receiver via HDMI or in analog form through multichannel analog audio connections. The audio signal passes through the receiver, the amplifier, and 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, or AV preamp/processor, you 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 connect to a home theater receiver using a digital audio connection (optical, coaxial, or HDMI), the surround sound audio bitstream is sent to the receiver, decoded, and sent through the amplifier and speakers. Suppose the media streamer is connected directly to a TV via HDMI and a compatible soundbar or home theater receiver via digital audio output or HDMI Audio Return Channel. In that case, the TV passes the bitstream signal 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. The TV might 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.

The Bottom Line

Bitstream encoding is a core technology 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 various connection options.