This section is for users who prefer to statically compile in support for the sound card in a custom kernel. For more information about recompiling a kernel, refer to 章 8, 設定 FreeBSD 核心.

When using a custom kernel to provide sound support, make sure that the audio framework driver exists in the custom kernel configuration file:

device sound

Next, add support for the sound card. To continue the example of the built-in audio chipset based on the Intel specification from the previous section, use the following line in the custom kernel configuration file:

device snd_hda

Be sure to read the manual page of the driver for the device name to use for the driver.

Non-PnP ISA sound cards may require the IRQ and I/O port settings of the card to be added to /boot/device.hints. During the boot process, loader(8) reads this file and passes the settings to the kernel. For example, an old Creative SoundBlaster® 16 ISA non-PnP card will use the snd_sbc(4) driver in conjunction with snd_sb16. For this card, the following lines must be added to the kernel configuration file:

device snd_sbc
device snd_sb16

If the card uses the 0x220 I/O port and IRQ 5, these lines must also be added to /boot/device.hints:

hint.sbc.0.at="isa"
hint.sbc.0.port="0x220"
hint.sbc.0.irq="5"
hint.sbc.0.drq="1"
hint.sbc.0.flags="0x15"

The syntax used in /boot/device.hints is described in sound(4) and the manual page for the driver of the sound card.

The settings shown above are the defaults. In some cases, the IRQ or other settings may need to be changed to match the card. Refer to snd_sbc(4) for more information about this card.

After loading the required module or rebooting into the custom kernel, the sound card should be detected. To confirm, run dmesg | grep pcm. This example is from a system with a built-in Conexant CX20590 chipset:

pcm0: <NVIDIA (0x001c) (HDMI/DP 8ch)> at nid 5 on hdaa0
pcm1: <NVIDIA (0x001c) (HDMI/DP 8ch)> at nid 6 on hdaa0
pcm2: <Conexant CX20590 (Analog 2.0+HP/2.0)> at nid 31,25 and 35,27 on hdaa1

The status of the sound card may also be checked using this command:

# cat /dev/sndstat
FreeBSD Audio Driver (newpcm: 64bit 2009061500/amd64)
Installed devices:
pcm0: <NVIDIA (0x001c) (HDMI/DP 8ch)> (play)
pcm1: <NVIDIA (0x001c) (HDMI/DP 8ch)> (play)
pcm2: <Conexant CX20590 (Analog 2.0+HP/2.0)> (play/rec) default

The output will vary depending upon the sound card. If no pcm devices are listed, double-check that the correct device driver was loaded or compiled into the kernel. The next section lists some common problems and their solutions.

If all goes well, the sound card should now work in FreeBSD. If the CD or DVD drive is properly connected to the sound card, one can insert an audio CD in the drive and play it with cdcontrol(1):

% cdcontrol -f /dev/acd0 play 1

Various applications, such as audio/workman, provide a friendlier interface. The audio/mpg123 port can be installed to listen to MP3 audio files.

Another quick way to test the card is to send data to /dev/dsp:

% cat filename > /dev/dsp

where filename can be any type of file. This command should produce some noise, confirming that the sound card is working.

Connecting to a Bluetooth device is out of scope for this chapter. Refer to 節 31.5, “藍牙” for more information.

To get Bluetooth sound sink working with FreeBSD's sound system, users have to install audio/virtual_oss first:

# pkg install virtual_oss

audio/virtual_oss requires cuse to be loaded into the kernel:

# kldload cuse

To load cuse during system startup, run this command:

# sysrc -f /boot/loader.conf cuse_load=yes

To use headphones as a sound sink with audio/virtual_oss, users need to create a virtual device after connecting to a Bluetooth audio device:

# virtual_oss -C 2 -c 2 -r 48000 -b 16 -s 768 -R /dev/null -P /dev/bluetooth/headphones -d dsp

請參考 virtual_oss(8) 取得更多資訊。

表格 7.1, “常見錯誤訊息” lists some common error messages and their solutions:

Modern graphics cards often come with their own sound driver for use with HDMI. This sound device is sometimes enumerated before the sound card meaning that the sound card will not be used as the default playback device. To check if this is the case, run dmesg and look for pcm. The output looks something like this:

...
hdac0: HDA Driver Revision: 20100226_0142
hdac1: HDA Driver Revision: 20100226_0142
hdac0: HDA Codec #0: NVidia (Unknown)
hdac0: HDA Codec #1: NVidia (Unknown)
hdac0: HDA Codec #2: NVidia (Unknown)
hdac0: HDA Codec #3: NVidia (Unknown)
pcm0: <HDA NVidia (Unknown) PCM #0 DisplayPort> at cad 0 nid 1 on hdac0
pcm1: <HDA NVidia (Unknown) PCM #0 DisplayPort> at cad 1 nid 1 on hdac0
pcm2: <HDA NVidia (Unknown) PCM #0 DisplayPort> at cad 2 nid 1 on hdac0
pcm3: <HDA NVidia (Unknown) PCM #0 DisplayPort> at cad 3 nid 1 on hdac0
hdac1: HDA Codec #2: Realtek ALC889
pcm4: <HDA Realtek ALC889 PCM #0 Analog> at cad 2 nid 1 on hdac1
pcm5: <HDA Realtek ALC889 PCM #1 Analog> at cad 2 nid 1 on hdac1
pcm6: <HDA Realtek ALC889 PCM #2 Digital> at cad 2 nid 1 on hdac1
pcm7: <HDA Realtek ALC889 PCM #3 Digital> at cad 2 nid 1 on hdac1
...

In this example, the graphics card (NVidia) has been enumerated before the sound card (Realtek ALC889). To use the sound card as the default playback device, change hw.snd.default_unit to the unit that should be used for playback:

# sysctl hw.snd.default_unit=n

where n is the number of the sound device to use. In this example, it should be 4. Make this change permanent by adding the following line to /etc/sysctl.conf:

hw.snd.default_unit=4

It is often desirable to have multiple sources of sound that are able to play simultaneously. FreeBSD uses “Virtual Sound Channels” to multiplex the sound card's playback by mixing sound in the kernel.

Three sysctl(8) knobs are available for configuring virtual channels:

# sysctl dev.pcm.0.play.vchans=4
# sysctl dev.pcm.0.rec.vchans=4
# sysctl hw.snd.maxautovchans=4

This example allocates four virtual channels, which is a practical number for everyday use. Both dev.pcm.0.play.vchans=4 and dev.pcm.0.rec.vchans=4 are configurable after a device has been attached and represent the number of virtual channels pcm0 has for playback and recording. Since the pcm module can be loaded independently of the hardware drivers, hw.snd.maxautovchans indicates how many virtual channels will be given to an audio device when it is attached. Refer to pcm(4) for more information.

The correct pcm device will automatically be allocated transparently to a program that requests /dev/dsp0.

The default values for the different mixer channels are hardcoded in the source code of the pcm(4) driver. While sound card mixer levels can be changed using mixer(8) or third-party applications and daemons, this is not a permanent solution. To instead set default mixer values at the driver level, define the appropriate values in /boot/device.hints, as seen in this example:

hint.pcm.0.vol="50"

This will set the volume channel to a default value of 50 when the pcm(4) module is loaded.