SoundCheck’s virtual instruments can be used to look at a signal in multiple ways. This article gives a brief overview of the differences between input virtual instruments. As an example, we'll be looking at pink noise.
The multimeter is used to measure the overall level. 50 millisecond time blocks are recorded and then averaged. It can be set to look at the maximum, minimum, average, or peak level. By default it measures across the entire available frequency band but high and low pass filters can be added to change the measurement spectrum.
The FFT has two different modes of operation: Spectrum and Time. The oscilloscope runs in the time domain and the spectrum analyzer runs in the frequency domain. Like the multimeter, all FFT data is analyzed in 50 millisecond time blocks. Instead of outputting a single value, the spectrum analyzer outputs an entire curve (frequency vs. level) and the oscilloscope outputs a waveform (time vs. level).
The RTA measures frequency bands in constant percentage bandwidth (1-N octave) filters. This is a recursive and continuous process, unlike the multimeter and FFT. The RTA can be set to different octave band widths. Changing this will affect how many frequencies are in each band, which in turn causes the level of each to change. As the filter width narrows, the level decreases in each individual band.
1/3 Octave Band RTA
1/24 Octave Band RTA. Take note of the perceived decrease in maximum level with the band increase.
For more in depth information, please refer to the “Virtual Instruments” chapter in the SoundCheck manual. For a live measurement demonstration, a "Virtual Instruments Acquisition Examples" sequence is included in the How To Examples folder of every SoundCheck installation.