freeswitch/conf/autoload_configs/portaudio.conf.xml

<configuration name="portaudio.conf" description="Soundcard Endpoint">
  <settings>
    <!-- indev, outdev, ringdev: 
	 partial case sensitive string match on something in the name 
	 or the device number prefixed with # eg "#1" (or blank for default) -->

    <!-- device to use for input -->
    <param name="indev" value="Built-in Input"/>
    <!-- device to use for output -->
    <!--<param name="outdev" value="Built-in Output"/>-->
    <param name="outdev" value="#2"/>

    <!--device to use for inbound ring -->
    <param name="ringdev" value="Built-in Output"/>

    <!--File to play as the ring sound -->
    <!--<param name="ring-file" value="/sounds/ring.wav"/>-->
    <!--Number of seconds to pause between rings -->
    <!--<param name="ring-interval" value="5"/>-->
    <!--Enable or Disable dual_streams-->
    <!--<param name="dual-streams" value="true"/>-->

    <!--file to play when calls are on hold-->
    <param name="hold-file" value="$${hold_music}"/>
    <!--Timer to use for hold music (i'd leave this one commented)-->
    <!--<param name="timer-name" value="soft"/>-->

    <!--Default dialplan and caller-id info -->
    <param name="dialplan" value="XML"/>
    <param name="cid-name" value="$${outbound_caller_name}"/>
    <param name="cid-num" value="$${outbound_caller_id}"/>

    <!--audio sample rate and interval -->
    <!--<param name="sample-rate" value="48000"/>-->
    <param name="sample-rate" value="8000"/>
    <param name="codec-ms" value="20"/>
  </settings>

  <shared-devices>
  	<device friendly-name="usb1" device="#2">
		<param name="channels" value="2" />
		<param name="sample-rate" value="8000" />
		<param name="codec-ms" value="20" />
  	</device>
  </shared-devices>

  <endpoints>

  	<endpoint name="usbout-left">
		<param name="outdev" value="usb1:0" />
	</endpoint>

  	<endpoint name="usbout-right">
		<param name="outdev" value="usb1:1" />
	</endpoint>

  </endpoints>

</configuration>