<sect2>

    <title>Utilizing Multiple Sound Sources</title>

    <para>It is often desirable to have multiple sources of sound that are able to

      play simultaneously, such as when <application>esound</application> or

      <application>artsd</application> don't support sharing of the sound device

      with a certain application.</para>

    <para>FreeBSD lets you do this through `Virtual Sound Channels', which can be

      set with the &man.sysctl.8; facility. Virtual channels allow you to multiplex

      your sound card's playback channels by mixing sound in the kernel.</para>

    <para>To set the number of virtual channels, there are two sysctl knobs which, 

      if you are the <username>root</username> user, can be set like this:</para>

    <screen>&prompt.root; sysctl hw.snd.pcm0.vchans=4 &prompt.root;

      sysctl hw.snd.maxautovchans=4</screen>

    <para><literal>hw.snd.pcm0.vchans</literal> is the number of vchans pcm0 has, 

      and is configurable once a device has been attached.<literal>hw.snd.maxautovchans

      </literal> is the number of vchans a new audio device is given when it is

      attached using &man.kldload.8;. Since the pcm module can be loaded independently 

      of the hardware drivers, <literal>hw.snd.maxautovchans</literal> can store how

      many vchans any devices which are attached later will be given.</para>

    <para>If you are not using &man.devfs.5;, you will have to point your applications

      at <devicename>/dev/dsp0</devicename>.x, where 'x' is 0 to 3 if <literal>

      hw.snd.pcm.0.vchans</literal> is set to 4. On a system using devfs, the above 

      will automatically be allocated transparently to the user.</para>