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Using the ALSA Sound System

This page summarises things I learned while trying to understand and use the Advanced Linux Sound Architecture (ALSA) on my Debian GNU/Linux system. I would be happy to receive suggestions to improve or extend this web page.

• "control" (used by the system to set the volume, mute channels, etc.)
• "playback"
• "capture" (reading audio data into the computer)
• "raw midi"
• "sequencer"
• "timer" (I don't know yet what the latter two do).

Tuning USB devices for minimal latencies¶

On linux-audio-user Christoph Eckert brought up the question about how to get better latencies out of USB audio devices, and USB guru Clemens Ladisch had a very good tip: The snd-usb-audio module accepts a module option called "nrpacks", which according to modinfo, sets the: Max. number of packets per URB. (int). Setting this to "nrpacks=1" should allow latencies in the area of 4-6 msecs.

Unfortunatly on some systems/kernels nrpacks=1 conflicts with a feature called "USB bandwidth allocation" in the kernel. Here's the way out:

• In the kernel config ensure that both options (taken from a 2.6.10) are disabled::
  

  :[   ] Enforce USB bandwidth allocation (EXPERIMENTAL)
  :[   ] Dynamic USB minor allocation (EXPERIMENTAL)
  

• Ensure to load the snd-usb-audio module with the parameter "nrpacks=1", maybe including it into one of the boot scripts::
  

  modprobe snd-usb-audio nrpacks=1
  

• Or use the module configuration line (e.g. in /etc/modprobe.conf):
  

  options snd-usb-audio nrpacks=1
  

http://alsa.opensrc.org/index.php/MultipleUSBAudioDevices

hernad@nmraka-1:~$ modinfo snd-usb-audio

filename:       /lib/modules/2.6.24-12-generic/ubuntu/sound/alsa-driver/usb/snd-usb-audio.ko
license:        GPL
description:    USB Audio
author:         Takashi Iwai <tiwai@suse.de>
srcversion:     DBC90B277D513C9230BEAB2
alias:          usb:v*p*d*dc*dsc*dp*ic01isc01ip*
alias:          usb:v*p*d*dc*dsc*dp*ic01isc03ip*
alias:          usb:v7104p2202d*dc*dsc*dp*ic*isc*ip*
alias:          usb:v4752p0011d*dc*dsc*dp*ic*isc*ip*

...

alias:          usb:v046Dp08AEd*dc*dsc*dp*ic01isc01ip*
alias:          usb:v046Dp0850d*dc*dsc*dp*ic01isc01ip*
depends:        snd-usb-lib,snd-pcm,usbcore,snd,snd-hwdep
vermagic:       2.6.24-12-generic SMP mod_unload 
parm:           index:Index value for the USB audio adapter. (array of int)
parm:           id:ID string for the USB audio adapter. (array of charp)
parm:           enable:Enable USB audio adapter. (array of bool)
parm:           vid:Vendor ID for the USB audio device. (array of int)
parm:           pid:Product ID for the USB audio device. (array of int)
parm:           nrpacks:Max. number of packets per URB. (int)
parm:           async_unlink:Use async unlink mode. (bool)
parm:           device_setup:Specific device setup (if needed). (array of int)

http://alsa.opensrc.org/index.php/Hotplugging_USB_audio_devices_(Howto)

...

Get Hotplug to switch setups¶

Hotplug has a collection of usermap files. These maps identify a specific device (by vendor id, device id, etc.) and instruct hotplug to execute a specific script that sets up the device. The usermaps can be created per device. In this example, I use /etc/hotplug/usb/extigy.usermap for the usermap and /etc/hotplug/usb/extigy for the script that it executes.
[edit] Create a usermap file

Figure out the vendor ID and product ID of your soundcard. You can either use lsusb -v or search for them on the web. For my SB Extigy, these are 041e and 3000 respectively.

The usermap file contains several fields. The first one is the name of the script, the second one is a mask that enables the match criteria. We have the produce and vendor id, so we use those:

/etc/hotplug/usb/extigy.usermap:

# usb module
# |       match_flags
# |       |       idVendor
# |       |       |       idProduct
# |       |       |       |       bcdDevice_lo
# |       |       |       |       |       bcdDevice_hi
# |       |       |       |       |       |       bDeviceClass
# |       |       |       |       |       |       |     bDeviceSubClass
# |       |       |       |       |       |       |     |     bDeviceProtocol
# |       |       |       |       |       |       |     |     |     bInterfaceClass
# |       |       |       |       |       |       |     |     |     |     bInterfaceSubClass
# |       |       |       |       |       |       |     |     |     |     |     bInterfaceProtocol
# |       |       |       |       |       |       |     |     |     |     |     |     driver_info
  extigy  0x0003  0x041e  0x3000  0x0000  0x0000  0x00  0x00  0x00  0x00  0x00  0x00  0x00000000

Now with this file, I got multiple calls of the script, presumably because the card has several subdevices. I restricted my script to apply only to the control interface (bInterfaceSubClass 1) so that I get one call only, YMMV.

/etc/hotplug/usb/extigy.usermap:

# usb module
# |       match_flags
# |       |       idVendor
# |       |       |       idProduct
# |       |       |       |       bcdDevice_lo
# |       |       |       |       |       bcdDevice_hi
# |       |       |       |       |       |       bDeviceClass
# |       |       |       |       |       |       |     bDeviceSubClass
# |       |       |       |       |       |       |     |     bDeviceProtocol
# |       |       |       |       |       |       |     |     |     bInterfaceClass
# |       |       |       |       |       |       |     |     |     |     bInterfaceSubClass
# |       |       |       |       |       |       |     |     |     |     |     bInterfaceProtocol
# |       |       |       |       |       |       |     |     |     |     |     |     driver_info
  extigy  0x0003  0x041e  0x3000  0x0000  0x0000  0x00  0x00  0x00  0x00  0x01  0x00  0x00000000

The hotplug script

This is a simple shell script. REMOVER is a variable passed to the script from hotplug which identifies the location of a script that is executed on removal. Unfortunately, the usb.agent script does not seem to work correctly. This is a known bug and you can find a workaround in the bug report.

/etc/hotplug/usb/extigy:

   #!/bin/bash
   #determine which configuration is active, note that removal does not seem to work
   echo -e "/usr/local/sbin/alsaswitch `ls -lFA /etc/asound.conf \
                                        | sed 's:.*/etc/alsa/asound.\([^ ]*\)$:\1:'`" > $REMOVER
   chmod a+x $REMOVER
   /usr/local/sbin/alsaswitch extigy;

Now all you need is to plug in your device. If you have coldplugging installed, this also works at boot time.

http://alsa.opensrc.org/index.php/.asoundrc

We can use it as follows:

pcm.nvidia {
type hw
card 0
device 0
}

pcm_slave.sl3 {
pcm nvidia
format S16_LE
channels 1
rate 16000
}
pcm.complex_convert {
type plug
slave sl3
}

By calling it with:

aplay -vD complex_convert test.wav

you can convert the samples during playing to the sample format: S16_LE, one channel and a sample-rate of 16 kHz. If you use aplay with the verbose option -v you will see the settings from the original file. For example,

aplay -v test.wav

will show the original settings of the sound file test.wav. If you add the definition "route_policy average" to the plug definition, you will make your output channel be the (arithmetic) average of your input channels.

ali ovo kod mene ne radi :(, vjerovatno jer ovdje imam pulseaudio

ni ovo ne radi ?!

hernad@nmraka-1:~$ aplay -D nvidia /usr/share/sounds/warning.wav

Playing WAVE '/usr/share/sounds/warning.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Mono
aplay: set_params:906: Channels count non available

evo šta kaže pulseaudio play

hernad@nmraka-1:~$ paplay -v /usr/share/sounds/warning.wav

Using sample spec 's16le 1ch 44100Hz'
E: shm.c: shm_open() failed: Permission denied
Connection established.
Stream successfully created
Playback stream drained.
Draining connection to server.

hernad@nmraka-1:~$ pactl stat

E: shm.c: shm_open() failed: Permission denied
Currently in use: 2 blocks containing 1.6 MiB bytes total.
Allocated during whole lifetime: 94020 blocks containing 328.4 MiB bytes total.
Sample cache size: 1.6 MiB
User name: hernad
Host Name: nmraka-1.sigma-com.net
Server Name: pulseaudio
Server Version: 0.9.9
Default Sample Specification: s16le 2ch 44100Hz
Default Sink: alsa_output.pci_10de_55c_sound_card_0_alsa_playback_0
Default Source: alsa_input.pci_10de_55c_sound_card_0_alsa_capture_0

http://www.linux-usb.org/

• 0000 Optical mouse
• 0001 Notebook Optical Mouse
• 0201 Defender Office Keyboard (K7310) S Zodiak KM-9010
• 9003 VoIP Conference Hub (A16GH)
• 9004 USR9602 USB Internet Mini Phone

iako zastarjelo: http://developer.novell.com/wiki/index.php/Edgy/HOWTO:_PulseAudio

probao ovo na visti ali stvar ne radi

default.pa

load-module module-waveout

load-module module-native-protocol-tcp auth-ip-acl=127.0.0.1;192.168.45.0/24

C:\Users\hernad\Desktop\pulseaudio-0.9.6>pulseaudio

W: pulsecore/random.c: failed to get proper entropy. Falling back to seeding wit
h current time.
W: pulsecore/core-util.c: secure directory creation not supported on Win32.
E: pulsecore/pid.c: stale PID file, overwriting.
W: pulsecore/core.c: failed to allocate shared memory pool. Falling back to a no
rmal memory pool.
E: modules/module-waveout.c: failed to open waveIn
E: pulsecore/module.c: Failed to load  module "module-waveout" (argument: ""): i
nitialization failed.
E: daemon/main.c: Module load failed.
E: daemon/main.c: failed to initialize daemon.