rnagarajanmca/raspberrypi_usb_audio.md

## raspberrypi_usb_audio.md

      
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              raspberrypi_usb_audio.md
            
          
    Device specifications


Raspberry pi - Any
USB Audio Adapter - USB Adapter
USB Hub - Zebronics USB Hub

List USB Device

Once you connected the USB Audio device with Raspberry pi use following command to see the list of connected USB device
lsusb
Above command will respond with list of USB devices the response will be similar like
Bus 001 Device 004: ID 1b3f:2008 Generalplus Technology Inc.
Bus 001 Device 003: ID 148f:7601 Ralink Technology, Corp.
Bus 001 Device 002: ID 05e3:0606 Genesys Logic, Inc. USB 2.0 Hub / D-Link DUB-H4 USB 2.0 Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Use following command to check whether USB audio device identified by Raspberry pi
pi@raspberrypi:~$ aplay -l

**** List of PLAYBACK Hardware Devices ****
card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 8/8
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
  Subdevice #7: subdevice #7
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: Device [USB Audio Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

From the above response we can understand card 1 is USB audio device
Configure USB Audio device as default device

We can configure default audio devices using Alsa.

Advanced Linux Sound Architecture (ALSA) is a software framework is part of the linux so we should be able to modify the conf file and set the default audio device
Use
Alsa Configuration file will be available under /etc/modprobe.d/alsa-base.conf. If the file is not available create one and put the following lines to reorder the audio devices
# This sets the index value of the cards but doesn't reorder.
options snd_usb_audio index=0
options snd_bcm2835 index=1

# Does the reordering.
options snd slots=snd_usb_audio,snd_bcm2835

pi@raspberrypi:~$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: Device [USB Audio Device], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 8/8
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
  Subdevice #7: subdevice #7
card 1: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
Now if you check the hardware order using aplay -l, Audio devices will be displayed as following order
Then you should set the external device as default device by editing the file ~/.asoundrc. type following lines in the asoundrc file
pcm.!default plughw:Device

ctl.!default plughw:Device

Test the Audio

Use following command to test the audio output
# -D - Device 
# -c Channels 
pi@raspberrypi:~$ speaker-test -t wav -c 2 -D hw:0

speaker-test 1.0.28

Playback device is hw:0
Stream parameters are 48000Hz, S16_LE, 2 channels
WAV file(s)
Rate set to 48000Hz (requested 48000Hz)
Buffer size range from 96 to 262144
Period size range from 48 to 131072
Using max buffer size 262144
Periods = 4
was set period_size = 65536
was set buffer_size = 262144
 0 - Front Left
 1 - Front Right
Time per period = 5.545710
 0 - Front Left
 1 - Front Right
Time per period = 5.539851
You can play the songs by usiong following command
pi@raspberrypi:~$ aplay  /usr/share/scratch/Media/Sounds/Animal/Bird.wav
Playing WAVE '/usr/share/scratch/Media/Sounds/Animal/Bird.wav' : Signed 16 bit Little Endian, Rate 11025 Hz, Mono
Troubleshoot


When you find following error when playing audio
 pi@raspberrypi:~$ aplay /usr/share/scratch/Media/Sounds/Animal/Bird.wav
 Playing WAVE '/usr/share/scratch/Media/Sounds/Animal/Bird.wav' : Signed 16 bit Little Endian, Rate 11025 Hz, Mono
 aplay: set_params:1239: Channels count non available
Do the following: Change the file ~/.asoundrc and set default device
If you are planning to configure different hardware for mic and speaker change ~/.asoundrc as mentioned below
 pcm.!default {
 type asym
 	playback.pcm{
 		type plug
 		slave.pcm "hw:0,0"
 	}
 	capture.pcm{
 		type plug
 		slave.pcm "hw:0,0"
 	}
 }

In my above configuration my both device connected in hardware card 0,
Configuration parameters in asoundrc file changes when rebooting RPi
If you face this issue create a file under /etc/asound.conf and put the following lines into it and reboot
 pcm.!default {
   type asym
    playback.pcm {
      type plug
      slave.pcm "hw:0,0"
    }
    capture.pcm {
      type plug
      slave.pcm "hw:1,0"
    }
 }