KC6HUR(-L)

There is much confusion in the IRLP world as to what control does what, when configuring the Sound Blaster using aumix. After digging around on the web for a day, I was able to gather enough information to generate the diagrams found below.

These diagrams are fairly generic and your Sound Blaster card may have different, more or fewer connections than shown below; however, what is shown here are the ones that are important to IRLP node operation.

What I have done is group things into Output Mixing Paths and Input Mixing Paths. They are shown as separate entities; however, they are interconnected. Where the input of a Mute switch connects to the output of a volume control, the input of a record switch connects to the same point. For illustration purposes, it was just easier to split things apart.

Figure 1 provides a fairly generic view of how audio signals get routed to the output of the Sound Blaster card. When working with IRLP, the signals we are most concerned with are PCM and if you have CW IDing configured on your node, then the SYNTH signal is also used. Some Sound Blaster card do not have the SYNTH signal source. Some have MIDI instead.

For normal IRLP operation, the MIC IN and LINE IN signals should be muted. That is to say, they are not routed to the Sound Blaster output jacks. This is an absolute necessity if any kind of full-duplex operation is planned.

Some Sound Blaster cards do not have the SPEAKER output connection but only offer a LINE OUT connection. In general, the LINE OUT is the output to use since is provides a signal level that is more readily interfaced to the input on a radio.

The OGain control also seems to be one of those items which varies from board to board. My Sound Blaster ViBRA 16 does not appear to have this control.

At any rate, the set of controls that affect the level and quality of the audio going from your node to your radio are: PCM, Volume, Treble, Bass and possibly OGain. How to set these levels will be discussed in another section.

Getting the audio from your radio to the node is fairly simple. You will be using either the LINE IN (preferred method) or the MIC IN. There are only two level controls involved with this setup: LINE or MIC and IGain. Some Sound Blaster card don't seems to have the IGain control (my ViBRA 16 appears to be one of those). Again, how to set these levels will be discussed in another section.