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Softmixer controller for 4A (AGL Advance Audio Architecture).

  • Object: Simulate a hardware mixer through and snd-aloop driver and a user space mixer
  • Status: In Progress
  • Author: Fulup Ar Foll fulup@iot.bzh
  • Author: Thierry Bultel thierry.bultel@iot.bzh
  • Date : July-2018

Features

  • Definition of multiple audio zones, and multiple audio cards
  • Usage of streams to access audio zones
  • Direct read from HW capture devices (eg radio chips & microphones)

Attach verb json format (TO UPDATE)

  • The uid field will be the name of the mixer corresponding to your hal.
  • The mixerapi field should contain the name of the api to call for reaching the mixer (not need to be changed if you use '4a-softmixer').
  • The prefix field is not mandatory, it is where you precise the prefix that will be applied when the mixer attach call happens. All the streams the mixer creates will be prefixed with this field.
  • In ramps section:
  • Define the ramp that you can use in your mixer (ramps in example files can be used).
  • The uid field is where you specify the name of the ramp.
  • The ramp will set the current volume to the targeted volume step by step:
  • The delay field is the delay between two volume modification.
  • The up field is the volume increase in one step (when increasing volume is requested).
  • The down field is the volume decrease in one step (when decreasing volume is requested).
  • The playbacks section will contain your output audio information (such as the path to you alsa audio device and the configuration of your device):
  • A uid field that will be used by the mixer to identify the playback.
  • The params field is an optional field where you can specify some parameters for your playback (such as rate).
  • The sink field is where you describe your playback:
  • The controls field must contain the alsa control labels that the mixer will use to set/mute volume on your audio device.
  • The channels field must contain an object that will link an uid to a physical output audio port that will be used in zone.
  • The captures section will contain your input audio information (such as the path to you alsa audio device and the configuration of your device):
  • A uid field that will be used by the mixer to identify the capture.
  • The params field is an optional field where you can specify some parameters for your capture (such as rate).
  • The sink field is where you describe your capture:
  • The controls field must contain the alsa control labels that the mixer will use to set/mute volume on your audio device.
  • The channels field must contain an object that will link an uid to a physical input audio port that will be used in zone.
  • In zones section: (zones in example files can be used):
  • You can define the zones that you want for your mixer.
  • You must define which sink will be used in these zones.
  • These zones will be used to define streams.
  • The sink field must contain objects that will link a physical ouput audio port (defined in playbacks section) using target field to a logical output audio channel that will be used in zone.
  • The source field must contain objects that will link a physical input audio port (defined in captures section) using target field to a logical input audio channel that will be used in zone.
  • In streams section: (streams in example files can be used):
  • You can define the streams that you want for your mixer.
  • Mandatory fields:
  • A uid field, it is the name used by the mixer to identify streams (e.g. when using info verb)
  • The verb field is the name used by the mixer to declare the stream verb (but prefixing it with prefix if defined). It is also used by the hal to declare a verb to make it accessible from a hal point of view.
  • The zone field must correspond to the wanted zone of the stream.
  • Optional fields:
  • The source is where you can precise which loop to use for this stream (not the default one). The loop are defined in the mixer configuration file.
  • The params is where you can specify some parameters for your stream (such as rate).
  • volume and mute fields are initiate values of the stream.

NOTE : This json format is used by 4a-hal-generic.

Compile

    mkdir build
    cd build
    cmake ..
    make

Install Alsa Loopback Driver

    sudo modprobe snd-aloop

Assert LUA config file match your config

    vim $PROJECT_ROOT/conf.d/project/lua.d/softmixer-01.lua

    # make sure both your loopback and targeted sound card path are valid

Run from shell

    afb-daemon --name 4a-softmixer-afbd --port=1234 --workdir=/home/fulup/Workspace/Audio-4a/4a-softmixer/build \
               --binding=package/lib/softmixer-binding.so --roothttp=package/htdocs --token= --tracereq=common --verbose

    # lua test script should return a response looking like
    response= {
      [1] = { ["uid"] = navigation,["runid"] = 101,["alsa"] = hw:5,0,6,["volid"] = 103,}
            , ["params"] = { ["channels"] = 2,["format"] = 2,["rate"] = 48000,["access"] = 3,} 
     ,[2] = {  ....
    }

    # runid: pause/resume alsa control you may change it with 'amixer -D hw:Loopback cset numid=101 on|off
    # volid: volume alsa control you may change it from 'alsamixer -Dhw:Loppback' or with 'amixer -D hw:Loopback cset numid=103 NN (o-100%)

Retrieve audio-stream alsa endpoint from response to 'L2C:snd_streams' command. Depending on your config 'hw:XXX' will change. Alsa snd-aloop impose '0' as playback device. Soft mixer will start from last subdevice and allocates one subdev for each audio-stream.

Play some music

snd-aloop only supports these audio formats:

S16_LE S16_BE S32_LE S32_BE FLOAT_LE FLOAT_BE

Using gstreamer is a simple way to perform the conversion, if your audio file is not of one of these.

    gst-launch-1.0 filesrc location=insane.wav ! wavparse ! audioconvert ! audioresample ! alsasink device=hw:Loopback,0,2

Warning

Alsa tries to automatically store current state into /var/lib/alsa/asound.state when developing/testing this may create impossible situation. In order to clean up your Alsa snd-aloop config, a simple "rmmod" might not be enough in some case you may have to delete /var/lib/alsa/asound.state before applying "modprobe".

In case of doubt check with folling command that you start from a clear green field

rmmod snd-aloop && modprobe --first-time  snd-aloop && amixer -D hw:Loopback controls | grep vol

Work in Progress

  • Support capture from bluez

Known issues

  • From times to times, playing an audio file make the sound output with higher pitch
  • The playback loop could be improved, using direct access to the ring buffer instead of copies to stack (could save some CPU time)