ASHA hearing aid simulation with Bumble

ASHA (Audio Streaming for Hearing Aids) is the Google protocol used by Android to stream audio to BLE hearing aids. Soundscape uses ASHA to send navigation audio directly to a user’s hearing aids. This page explains how to run a simulated hearing aid on a Linux PC using Google Bumble, so that you can test the ASHA connection path without needing a real hearing aid device.

Hardware requirements

You need a Bluetooth 4.0 or later USB dongle with LE support on the Linux machine running the simulation. ASHA requires BLE; BT 1.x/2.x/3.x dongles will not work.

A dongle that has been confirmed to work is the BT820 (USB ID 0a12:0001, reports BLUETOOTH_CORE_4_0). Dongles reporting BT 5.0 should also work.

Setting up Bumble

Clone the Bumble repository and create a virtual environment:

git clone https://github.com/google/bumble.git
cd bumble
python3 -m venv .venv
.venv/bin/pip install -e ".[development]"

Required patch to `run_asha_sink.py`

The upstream examples/run_asha_sink.py uses the extended advertising API (create_advertising_set), which requires a BT 5.0 controller and is also not recognised as legacy advertising by Android’s ASHA scanner. Apply the following change before running:

In examples/run_asha_sink.py, replace the import line:

from bumble.device import AdvertisingEventProperties, AdvertisingParameters, Device

with:

from bumble.device import Device

And replace the create_advertising_set call:

await device.create_advertising_set(
    auto_restart=True,
    advertising_data=advertising_data,
    advertising_parameters=AdvertisingParameters(
        primary_advertising_interval_min=100,
        primary_advertising_interval_max=100,
    ),
)

with:

await device.start_advertising(
    auto_restart=True,
    advertising_data=advertising_data,
    advertising_interval_min=100,
    advertising_interval_max=100,
)

start_advertising automatically falls back to legacy HCI advertising commands when the controller does not support extended advertising, and produces legacy advertising PDUs that Android’s hearing aid scanner can discover.

Running the simulation

Bumble takes direct control of the USB dongle, bypassing the kernel Bluetooth stack, so it needs root (or a udev rule granting access to the device). From the bumble directory:

sudo .venv/bin/python3 examples/run_asha_sink.py examples/device1.json usb:0

usb:0 selects the first USB Bluetooth dongle. If you have more than one, use usb:1, usb:2, etc. The device1.json config gives the simulated device a fixed random address (F0:F1:F2:F3:F4:F5) and name (Bumble).

A successful start looks like:

D bumble.host: ### CONTROLLER -> HOST: HCI_COMMAND_COMPLETE_EVENT:
  command_opcode: HCI_LE_SET_ADVERTISE_ENABLE_COMMAND
  return_parameters:
    status: SUCCESS

The device is now advertising and waiting for a connection.

Connecting from an Android phone

Soundscape targets Android 10+. ASHA device discovery is handled by the Android OS, not by a regular Bluetooth scan. To pair:

Go to Settings → Accessibility → Hearing devices (the exact path varies slightly between Android versions and OEM skins — search for “Hearing” in Settings if you can’t find it).
Tap Add device or Pair new hearing aid.
The phone will scan and should find Bumble. Tap it to pair.

Once paired, the phone will reconnect automatically whenever the simulation is running and Soundscape will be able to stream audio to it via the ASHA profile.

Troubleshooting

Device not found during scan

Confirm the simulation started cleanly and reached the HCI_LE_SET_ADVERTISE_ENABLE_COMMAND SUCCESS line.
Make sure you are looking in Accessibility → Hearing devices, not the regular Bluetooth settings — ASHA devices do not appear in the standard Bluetooth device list.
If you previously attempted to pair before applying the patch above, clear any cached entry in the Android hearing device list and try again.

UNKNOWN_HCI_COMMAND_ERROR on startup

Your dongle does not support extended advertising (it is BT 4.x). Make sure the patch above has been applied — start_advertising handles this automatically.

INVALID_COMMAND_PARAMETERS_ERROR on HCI_SET_EVENT_MASK_COMMAND and immediate crash

Your dongle is Bluetooth 1.2 (or earlier) and cannot support ASHA. Replace it with a BT 4.0+ LE-capable dongle.

usb:0 picks the wrong device

Run lsusb to list USB devices and identify which bus/device number your Bluetooth dongle is. Then use usb:<index> to select it (Bumble numbers dongles starting from 0 in the order they appear on the bus).