7.2. 設定音效卡

7.2.1. 設定系統

開始設定之前，必須先知道你的音效卡型號、晶片為何，以及是 PCI 或 ISA 規格。 FreeBSD 有支援許多種的 PCI、ISA 音效卡，請檢查支援的音效硬體表 Hardware Notes，以確認你的音效卡是否支援。 本文也會提到相對應該卡的驅動程式。

要使用音效卡，必須要載入正確的驅動程式才行。有兩種方式都可以完成這動作， 最簡單方式就是以 kldload(8) 來輕鬆載入 kernel 動態模組(module)， 像是下列指令：

# kldload snd_emu10k1

或者把相關驅動程式加到 /boot/loader.conf 檔，像是：

snd_emu10k1_load="YES"

上面例子是給 Creative SoundBlaster® Live! 音效卡使用的。 其他可用的音效卡驅動程式模組，可參考 /boot/defaults/loader.conf 範例。 若不確定到底該用哪一種驅動程式，那麼可以試試載入 snd_driver 模組看看：

# kldload snd_driver

This is a metadriver loading the most common device drivers at once. This speeds up the search for the correct driver. It is also possible to load all sound drivers via the /boot/loader.conf facility.

If you wish to find out the driver selected for your soundcard after loading the snd_driver metadriver, you may check the /dev/sndstat file with the cat /dev/sndstat command.

A second method is to statically compile in support for your sound card in your kernel. The section below provides the information you need to add support for your hardware in this manner. For more information about recompiling your kernel, please see µÚ 8 章.

device sound

device pcm

device snd_emu10k1

device snd_sbc
device snd_sb16

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"

device sbc0 at isa? port 0x220 irq 5 drq 1 flags 0x15

7.2.2. Testing the Sound Card

After rebooting with the modified kernel, or after loading the required module, the sound card should appear in your system message buffer (dmesg(8)) as something like:

pcm0: <Intel ICH3 (82801CA)> port 0xdc80-0xdcbf,0xd800-0xd8ff irq 5 at device 31.5 on pci0
pcm0: [GIANT-LOCKED]
pcm0: <Cirrus Logic CS4205 AC97 Codec>

The status of the sound card may be checked via the /dev/sndstat file:

# cat /dev/sndstat
FreeBSD Audio Driver (newpcm)
Installed devices:
pcm0: <Intel ICH3 (82801CA)> at io 0xd800, 0xdc80 irq 5 bufsz 16384
kld snd_ich (1p/2r/0v channels duplex default)

The output from your system may vary. If no pcm devices show up, go back and review what was done earlier. Go through your kernel configuration file again and make sure the correct device is chosen. Common problems are listed in µÚ 7.2.2.1 節.

If all goes well, you should now have a functioning sound card. If your CD-ROM or DVD-ROM drive is properly coupled to your sound card, you can put a CD in the drive and play it with cdcontrol(1):

% cdcontrol -f /dev/acd0 play 1

Various applications, such as audio/workman can provide a friendlier interface. You may want to install an application such as audio/mpg123 to listen to MP3 audio files. A quick way to test the card is sending data to the /dev/dsp, like this:

% cat filename > /dev/dsp

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

Sound card mixer levels can be changed via the mixer(8) command. More details can be found in the mixer(8) manual page.

7.2.3. Utilizing Multiple Sound Sources

It is often desirable to have multiple sources of sound that are able to play simultaneously, such as when esound or artsd do not support sharing of the sound device with a certain application.

FreeBSD lets you do this through Virtual Sound Channels, which can be set with the sysctl(8) facility. Virtual channels allow you to multiplex your sound card's playback channels by mixing sound in the kernel.

To set the number of virtual channels, there are two sysctl knobs which, if you are the root user, can be set like this:

# sysctl hw.snd.pcm0.vchans=4
# sysctl hw.snd.maxautovchans=4

The above example allocates four virtual channels, which is a practical number for everyday use. hw.snd.pcm0.vchans is the number of virtual channels pcm0 has, and is configurable once a device has been attached. hw.snd.maxautovchans is the number of virtual channels a new audio device is given when it is attached using kldload(8). Since the pcm module can be loaded independently of the hardware drivers, hw.snd.maxautovchans can store how many virtual channels any devices which are attached later will be given.

If you are not using devfs(5), you will have to point your applications at /dev/dsp0.x, where x is 0 to 3 if hw.snd.pcm.0.vchans is set to 4 as in the above example. On a system using devfs(5), the above will automatically be allocated transparently to the user.

7.2.4. 設定預設(Mixer Channel)的音量大小

The default values for the different mixer channels are hardcoded in the sourcecode of the pcm(4) driver. There are a lot of different applications and daemons that allow you to set values for the mixer they remember and set each time they are started, but this is not a clean solution, we want to have default values at the driver level. This is accomplished by defining the appropriate values in /boot/device.hints. E.g.:

hint.pcm.0.vol="100"

This will set the volume channel to a default value of 100, when the pcm(4) module is loaded.