Contents - Index

SPL/Spectrum
Index
Use the SPL Meter/Spectrum Analyzer type to see sound levels from any acoustic source.  The Generator (in the top menu) can be used to generate one or two tones, or the Spectral Contamination tool can be used to generate larger numbers of tones. Either signal can be recorded to WAV files which can optionally be played on most modern audio/visual equpment).  This tab page provides a graph of level vs frequency and a meter indicating broadband level.

The level of any sounds on the SPL meter face.  
Options:
  • Select the meter damping type: Impulse, Fast, Slow or Slowest.   Damping determines how fast the needle moves in changing sound levels.  With Impulse type, there will be some error for lower frequencies, so if those are of interest, choose Fast instead of Impulse.
     
  • Read the Peak, Maximum or Minimum values sensed since the Reset button was last clicked
  • Choose the response weighting to use at the top of the tab page: A, B, C, or None.
  • When A weighting is selected, read the cumulative Sound Exposure Level (SEL) over time spans starting from a click of the Begin circle to a click of the End button.  The time span is shown on the readout along with the Leq (equivalent level).
  • In the Config menu, use the option "Show Large SPL" to change to a full screen display of the SPL level (only), with the settings pre-selected above, in large characters for easier reading at distance for level monitoring applications.

    The spectrum of any sounds, on the Spectrum Analyzer graph.
    Options:
  • Choose the FFT format for display in terms of 1.47Hz bandwidth.   This format allows you to choose the amount of smoothing applied.
  • Choose the RTA format is more traditional and simple, for display in terms of 1/6th octave frequency bandwidths.
  • Choose the response weighting shape to use for either at the top of the tab page: A, B, C, or None.
  • Don't use the Spectrum Analyzer to measure frequency response -- the Frequency Response analyzer is much better for that function!
  • Select the damping type for either analyzer graph from: None, Impulse, Fast, Slow or Slowest.  This determines how quickly the trace rises and settles in presence of changing levels.
  • The FFT analyzer has two options "Noise" and "Tones" when smoothing is being used.  These correspond to the types of signals being measured.  If a set of fixed frequency tones are being displayed (such as for sine waves or their distortion products), use "Tones".  If broadband signals, use "Noise".      This is because an analyzer must measure signal within some bandwidth, and pure tones have zero bandwidth.  Without smoothing, each point shows the energy within each 1.47Hz bandwidth and separated tones, though at correct level, will appear as barely visible lines.  When smoothing is used each tone appears wider, but each point on the trace is an average of levels over nearby frequencies.  If tones were input with a smoothed plot, it would cause those averaged levels to appear lower than the tone level because of low energy in most of that bandwidth.  The "Tones" mode compensates approximately for that (but noise in the plot will appear higher).
  • The FFT Spectrum Analyzer is also used in Spectral Contamination measurements.
  • Up to 9 "floating" markers can be placed on an RTA or FFT trace.  Position the mouse cursor over the graph at the frequency you want the marker placed at, and tap one of the keys for "1" through "9".  Tapping "0" will allow you to clear all floating markers.  Right-clicking on a floating marker will allow you to delete it individually.