SoundMeter features a whole or third-octave-band real-time spectrum analyzer (RTA) that employs order 3 digital Butterworth bandpass filters, as recommended by ANSI standards. Spectral measurements can be made with fast, slow, or impulse time-weighted exponential integration, with Z (flat), A, or C frequency weighting. Equivalent (long-time average) signal levels can be measured as well. In addition to recording the current average level, the octave band analyzer keeps track of max and peak levels and it can even display the max or peak level simultaneously with the current average level.
The Octave RTA also computes percentile-exceeded sound levels, Lx, for each frequency band.
The bar graph may be overlaid with noise criteria (NC), room noise criteria (RNC), or noise rating (NR) reference curves. The overall NC and NR values, in addition to the speech interference level (SIL), will also be calculated. Since these values are calculated for whole octave band data, if the current spectrum is measured in 1/3-octave bands, whole octave band data will be estimated by combining 1/3-octave bands in order to calculate the appropriate criterion value. NC and RNC curves, as well as NC and SIL values are determined as defined in ANSI S12.2-2008. NC, SIL, and NR values are calculated from Leq levels, regardless of which kind of level (Lp, Leq, or Lx) is being displayed in the plot.
A data cursor may be placed within the spectrum display with a single tap. You can move the data cursor by sliding your finger to the right or left inside the spectrum display. A double-tap turns off the data cursor. When the cursor is visible, spectrum information associated with the cursor is displayed in a small info view above the spectrum display. Cursor peak tracking can be cycled between max, min, and off with a triple tap.
The info view also displays the overall signal level, as well as the elapsed time from the time the measurement was started.
Depending on the current auto-scaling selection, the vertical scale of the spectrum graph may be altered by a single-finger slide, or with a two-finger pinching gesture inside the vertical axis region (the region containing the vertical axis title and labels). Adjustments made to the vertical spectrum scale also affect the color scale of the log plot.
When data logging* is enabled, logged levels are then displayed in a 2D color surface plot below the spectrum graph. The color scale is defined by the vertical scale of the spectrum graph. A data cursor may be placed within the log plot to identify specific levels associated with date, time, and frequency band. Data can be logged as often as every 0.1 seconds for up to 1 hour, every second for up to 10 hours, or every 10 seconds for up to two weeks. Larger intervals can also be specified in each case.
When data logging is enabled, logged levels will also be included when saving data to a CSV, TXT, or MAT file.