How Auracast works: source, assistant, receiver

Every Auracast broadcast involves three roles. Understanding them explains almost every compatibility question people ask.

The source

The source is whatever transmits. It can be a dongle in a laptop, a box on the back of a TV, a transmitter in a venue's audio rack, or a phone broadcasting its own music. A source sends one or more streams (the standard calls each one a BIS, a broadcast isochronous stream). A venue transmitter typically carries two: a theatre might broadcast the programme on one and audio description on the other; a cinema, two languages.

A source can broadcast openly, so anyone can join, or encrypted with a broadcast code. The code is usually delivered as a QR code on signage, which the Bluetooth SIG standardised in 2025 as Scan-to-Listen: scan it, and your phone has both the broadcast's identity and its key.

The source does not know who is listening. There is no connection to count. That is why there is no limit on the number of listeners and no slowdown as people join.

The receiver

The receiver is what plays the audio: earbuds, headphones, hearing aids, a speaker, or a dedicated receiver box with a headphone socket. It needs an LE Audio radio and firmware that implements the broadcast sink role.

This is where the confusion lives. "Bluetooth 5.3" on a box does not mean Auracast. "LE Audio" does not mean Auracast. Plenty of earbuds shipped with the radio and no firmware; some, like the Sennheiser Momentum True Wireless 5, still have no firmware a month after launch. The only reliable tests are: the manufacturer says the feature is live, the Bluetooth SIG lists the product in the receiver role, or someone has joined a broadcast with it. Our product database records which of those applies to each product.

The assistant

Here is the part that trips people up. Most receivers cannot see broadcasts on their own. Earbuds have no screen and hearing aids have no buttons to spare. So a third device, the assistant, scans for broadcasts, shows you the list, and tells the receiver which one to join.

The assistant is almost always your phone. On a Samsung, Pixel, Sony or Xiaomi phone it is built into the Bluetooth settings. On an iPhone it is not, so the job falls to the hearing-aid maker's app, which is why ReSound aids work from an iPhone and Widex aids do not. Some receivers, such as the LG xboom Buds Plus and the Avantree AuraClip, carry their own assistant and need no phone at all.

The assistant is a remote control. Once the receiver has joined, the audio flows straight from source to receiver. You can put the phone in your pocket, or let it die.

The codec

Auracast carries audio as LC3, the LE Audio codec. At 48 kHz it sounds as good as the AAC or aptX streams you are used to, at roughly half the bit rate, which is why LE Audio earbuds run longer on a charge. Venues often broadcast speech at 16 or 24 kHz to stretch range and battery.

Latency

A broadcast is one-way, so there is no handshake and no retransmission. Latency is set by the transmitter's buffering. Venue transmitters are tuned to under 40 milliseconds so that the broadcast stays in sync with the lips on stage. Consumer dongles sit between 50 and 120 milliseconds depending on the maker and the mode: fine for television, noticeable in a rhythm game. Where two measurements disagree, the product page says so.

Range

Range depends on transmit power. A USB dongle covers a large room. A venue transmitter at the maximum allowed power covers 100 metres and more, and transmitters can repeat one another to cover a stadium. Bodies absorb 2.4 GHz, so a packed room is shorter-ranged than an empty one; venue designers plan for that.

What this means in practice

• If your earbuds are in the database as working and your phone is a Samsung, Pixel, Xperia or Xiaomi, you can join any open broadcast today.
• If you carry an iPhone, you need hearing aids with an assistant app, or a receiver that finds broadcasts itself.
• If you want to broadcast your own TV, any transmitter in the database will do it, and we have a guide.