There are several ways to work with a multi-channel audio interface in AudioTools. For example, you may want to plug a USB audio interface into the USB-C connector on your iPad or iPhone to be able to use one more microphones plugged into it. The mic you want to use may not be in channel 1, or you may want to average several mics using our multiplexor, or run our Low SPL module to get lower ambient noise measurements. These use cases are discussed here.

Channel Mapping

Mapping is used to select the main microphone (L) that is used for all of the one-input modules, including RTA, SPL Meter, and more. It can also select channel 2 (normally R) that is used for functions like Transfer Function or Audio Scope. To set this up, go to Settings->Channel Mapper, and you will see the number of available channels on the top of the screen. Use the +/- buttons to select which channel on your audio interface that you want to use for these channels.

Now when you navigate to any module, the selected audio input will be used. Note the display will still show Mic Low Range or High Range.

Microphone Multiplexor

AudioTools includes a microphone multiplexor that cycles through a set of mics so that you can get a spatial average of a measurement. It is implemented in SPL Pro, RTA, FFT, and SoundScope.

While the Mux is active it disables Mapping completely.  When exiting any of these modules, or disabling the Mux, the previously set mapping, if any, is reapplied.

To set up the microphone multiplexor, or Mux, first plug in your multichannel interface, and set up the microphones around the room. Then, navigate to the Settings->Mux function. If you have two or more channels available, you will see the Mux setup screen. Here you can select and turn on as many channels as you would like to include in the microphone rotation selection. 

To calibrate microphones for the Mux, it is important to start by calibrating the microphone in channel 1 by using the normal  microphone calibration page. Once this has been done, open the Mux, and for microphones 2 above, tap the mic cell to select it, or use the selector on the bottom of the page, and first adjust the hardware gain to as close as possible to the calibrator setting, and then use the +/- trim to make any final needed adjustments. Note that if you change the calibration for mic 1 you will need to go back and adjust the other mics on the Mux page. 

Next, set the amount of time for the complete cycle. For example, if you have 4 microphones selected and a 10s Cycle Time, that will cause each microphone to be active for 2.5 seconds at a time.

Finally, turn on the Enable switch. Now, when you go to a tool like RTA or FFT that support the Mux feature, it will be active.

The microphone multiplexor is not available with iAudioInterface2.

Low SPL Module

Low SPL works a little differently, since it only works with two microphones. It bypasses mapping, and does not use the Mux. Simply select the two microphone channels directly in Low SPL setup. The calibration for these microphones however is taken from the main settings (mic 1) and the Mux settings page (mics 2 and above).