Sound-alsa

ALSA (Advanced Linux Sound Architecture)

My main focus when I write these pages is on getting sound to work properly with a Raspberry Pi. The techniques in these notes may work on other systems but I have created this page to keep track of RPi related sound information.

disabling the on-board sound card =

/etc/modules

/etc/modprobe.d/modules

(to be edited..)

measuring sound volume input level

• display the current input level of sound presented to the recording device

arecord -Dhw:0 -c2 -d 0 -fS16_LE /dev/null -vvv

It just starts a recording but sends the recording to /dev/null rather than saving it, and then around every 10ms it spits back a new line which looks like this:

Max peak (2000 samples): 0x000028ca ####### 31%

Max peak (2000 samples): 0x00002872 ####### 31%

Max peak (2000 samples): 0x000023de ###### 28%

Max peak (2000 samples): 0x00002bf3 ####### 34%

Max peak (2000 samples): 0x00002cb1 ####### 34%

• display the sound system's gain setting of the input channel

123

Nothing here yet

alsa config

/etc/asound.conf or ~/.asoundrc

 pcm.!default {
         type asym
         playback.pcm {
                 type plug
                 slave.pcm "hw:0,0"
         }
         capture.pcm {
                 type plug
                 slave.pcm "hw:1,0"
         } 
 }

This little ALSA configuration setting uses the default sound card as playback device (hw:0,0) and sets hw:1,0 (that suppose to be your USB-mic) to become the default capture device.

http://wiki.audacityteam.org/wiki/USB_mic_on_Linux