Broadcast Audio Multi Source

This application creates a stereo channel continuous loop Broadcast Audio Source, using pre-encoded audio, stored with the application in flash.

Using 16 KHz mono and an nRF52840 Dongle (with 1 MB flash), it's possible to store just below 1.5 minutes of pre-encoded stereo audio, which will be broadcasted in a continuous loop.

The application is a slightly modified version of the BAP Broadcast Source sample.

Getting started...

If you haven't done it yet, first go to The Zephyr getting started guide and install all dependencies (I'd recommend following the path with the virtual python environment).

For development

For developers of the application, first do a fork of the repo. Then do the following:

Make a local workspace folder (to hold the repo, zephyr and west modules):

mkdir my-workspace
cd my-workspace

Clone the repo:

git clone [email protected]:<your handle>/multi-source.git

Initialize west and update dependencies:

west init -l multi-source
west update

For normal use (non-development)

This repo contains a stand alone Zephyr application that can be fetched and initialized like this:

west init -m https://github.com/astraeuslabs/multi-source --mr main my-workspace

Then use west to fetch dependencies:

cd my-workspace
west update

Build and flash

Go to the repo folder:

cd multi-source

nRF5340 Audio DK board

The nRF5340 Audio DK has two cores - one for the application and one dedicated for the network (bluetooth controller).

Build the controller (from zephyr/samples/bluetooth/hci_ipc):

west build -b nrf5340_audio_dk_nrf5340_cpunet -d build/hci_ipc ../zephyr/samples/bluetooth/hci_ipc --pristine -- -DCONF_FILE=nrf5340_cpunet_iso-bt_ll_sw_split.conf

Build the application:

west build -b nrf5340_audio_dk_nrf5340_cpuapp -d build/app app --pristine

Clear all flash for the two cores with the recover command (only needed the first time):

nrfjprog --recover --coprocessor CP_NETWORK
nrfjprog --recover

And flash the two cores with the controller and application:

west flash -d build/hci_ipc
west flash -d build/app

nRF52840 Dongle

There are a few scripts for building and flashing the nRF52840 Dongle - run them in this order:

compile_app.sh
create_flash_package.sh
flash_dongle.sh

Note: You'll need to get the dongle in DFU mode by pressing the small side buttton with a nail. The dongle should then start fading a red light in and out.

Preparing the LC3 binary files

The application defaults to 16 KHz stereo but can be configured to use 24 KHz by enabling the following project configuration:

CONFIG_BAP_BROADCAST_24_2_1=y

First, prepare a mono WAV file in either 16 KHz or 24 KHz sample rate for each channel (left & right).

Note: for the nRF52840 Dongle, the maximum length for 16 KHz is just below 1.5 minutes of stereo audio, for 24 KHz it's just below 1 minute of stereo audio (to fit the flash memory).

The data is pre-encoded with the LC3 encoder tool available from the Google liblc3 project:

.../liblc3/bin$ ./elc3 -b 32000 input16KHz.wav output16KHz.lc3

or

.../liblc3/bin$ ./elc3 -b 48000 input24KHz.wav output24KHz.lc3

Then place the resulting lc3 file in the src folder - and modify the names in CMakeLists.txt:

...
generate_inc_file_for_target(app
src/output16KHz.lc3
${gen_dir}/output16KHz.lc3.inc)

generate_inc_file_for_target(app
src/output24KHz.lc3
${gen_dir}/output24KHz.lc3.inc)
...

and in main.c (e.g. for 16 KHz)

...
static const uint8_t lc3_left[] = {
#include "Sine1000Hz_1s_16.lc3.inc"
};

static const uint8_t lc3_right[] = {
#include "Sine1500Hz_1s_16.lc3.inc"
};
...

you can also modify the broadcast name:

#define BT_AUDIO_BROADCAST_NAME "Awesome Broadcast"