Auracast Broadcast Audio: Deployment and Use Cases

Auracast Broadcast Audio: Deployment and Use Cases

Auracast is the Bluetooth SIG brand name for BLE Broadcast Audio — public or private audio streaming to unlimited simultaneous listeners using Broadcast Isochronous Streams (BIS). Unlike classic A2DP (point-to-point), Auracast requires no pairing and no connection: a transmitter broadcasts, receivers tune in.

How Auracast Works

Transmitter (e.g., TV, PA system)
      │
      │  BIS (Broadcast Isochronous Stream)
      │  LC3 audio @ 32–96 kbps
      │  No pairing, no connection
      │
  ────┼────────────────── Radio
      │              │              │
   Receiver A    Receiver B    Receiver C
  (hearing aid)  (headphone)   (phone app)

The transmitter sends a Broadcast Audio Announcement in its Extended Advertising PDU, containing the Broadcast_ID and audio stream metadata. Receivers scan for this announcement, sync to the Periodic Advertising train to get BASE (Broadcast Audio Source Endpoint) information, then synchronize to the BIS.

Auracast Profiles

Transmitter Setup: nRF5340 Example

#include <bluetooth/audio/audio.h>
#include <bluetooth/audio/bap.h>

#define LC3_FREQUENCY   BT_AUDIO_CODEC_LC3_FREQ_48KHZ
#define LC3_FRAME_DURATION BT_AUDIO_CODEC_LC3_DURATION_10
#define LC3_BITRATE     48000U  /* 48 kbps per channel */

static struct bt_bap_broadcast_source *source;
static struct bt_bap_broadcast_source_create_param create_param = {
    .params_count = 1,
    .params       = &stream_params,
    .qos          = &broadcast_preset_48_2_1.qos,  /* 48 kHz, 10 ms frames, RTN=1 */
    .packing      = BT_ISO_PACKING_SEQUENTIAL,
    .encryption   = false,       /* set true + provide broadcast_code for private streams */
};

bt_bap_broadcast_source_create(&create_param, &source);
bt_bap_broadcast_source_start(source, adv);

For encrypted (private) Auracast streams, set encryption = true and provide a 16-byte broadcast_code — distributed out-of-band (QR code, NFC tap, app pairing).

Receiver Compatibility

As of 2025, Auracast receivers include:

The Bluetooth SIG Auracast qualification list is the authoritative receiver compatibility reference.

Audio Quality

LC3 (Low Complexity Communication Codec) delivers perceptually equivalent quality to SBC at half the bitrate. Common Auracast configurations:

RTN (Retransmission Number) adds audio redundancy. RTN=2 doubles air time but dramatically reduces packet-loss-induced dropout — important in crowded RF environments.

Venue Deployment Considerations

Coverage: BLE broadcast range is typically 10–30 m indoors. A 10,000 seat arena requires a distributed transmitter network or directional antenna arrays.

Multi-language support: Auracast supports multiple BIS streams (e.g., English, Spanish, ASL description) within one Broadcast Audio Source. Receivers choose their preferred stream from the BASE metadata.

Latency for live events: 48_2_1 achieves ~20 ms one-way audio latency. For lip-sync with video, the video stream must be delayed to match. Professional AV integration requires coordinating Auracast timing with video delay buffers.

RF coexistence: Auracast competes with Wi-Fi (2.4 GHz). In dense venues, use 5 GHz Wi-Fi offload and ensure Auracast transmitters use the three dedicated advertising channels plus isochronous channels on the least-congested data channels.

Use the BLE Range Calculator to model Auracast coverage areas for venue planning.