Multi-channel capture is a Pro upgrade feature that allows REW to capture multiple inputs simultaneously for measurement or for the RTA. Individual SPL metering is available for the first four inputs. Measurements made with multi-channel capture will show an rms average of all the captured channel magnitudes with an underlay showing the span of the individual channels and can optionally include individual measurements for each channel. Each input can have its own calibration file.
Multi-channel capture would typically be used with a mic array (such as the miniDSP UMIK-X) or a multi-channel interface with multiple analog microphones connected to it. REW captures a contiguous range of input channels. Whilst it is possible to use this feature with multiple USB microphones on Windows when using an ASIO wrapper, this is NOT recommended because:
RTA measurements with multi-channel capture show an rms average of all the captured channel magnitudes.
The first and last channels to be captured are selected on the Soundcard preferences or the Measure dialog. The example below shows selection using ASIO drivers, a similar selection is offered for Java drivers. Note that Java drivers on Windows are limited to two channels, ASIO must be used for multi-channel devices. On macOS or Linux Java drivers offer as many channels as the interface supports.
When using the miniDSP UMIK-X there is an option on the Measure dialog to produce an average of the four mics on each UMA4 mic array as well as an overall average of all the selected inputs. The array average measurement names will be prefixed with "A1-" for the first array, "A2-" for the second and so on.