Spectrogram Display Options

Scale Options

  • Autoscale
    Autoscale enables the magnitude scale and range to be set automatically, which can make it easier to keep the signal visible in the plot. Sometimes, when a measurement doesn't appear as expected, setting Autoscale to Auto can solve the problem. When autoscale is off, the vertical scale of the plot can be manually adjusted by a two-finger pinch gesture within the axis label region of the plot. The range can be adjusted by a single-finger slide gesture within the axis label region.
  • Magnitude Values
    Three scale types are available for viewing spectral magnitude data: Linear, Logarithmic, and dB. The desired scale type is determined by the selection of this control and represented using color in the spectrogram.
  • Magnitude Scale
    Tap on Magnitude Scale to select a vertical scale for the plot in standard units per division. Autoscale will be turned off. If the Vertical Axis option is set to dB, changing the Magnitude Scale will switch it to Lin.
  • dB Magnitude Scale
    Tap on dB Magnitude Scale to select a vertical scale for the plot in dB per division. Autoscale will be turned off. If the Vertical Axis option is switched to Lin or Log, changing the dB Magnitude Scale will switch it to dB.
  • Frequency Axis
    Two frequency scale types are available for viewing spectra: Linear and Logarithmic. The desired scale type is determined by the selection of this control.
  • Frequency Units
    This segmented control lets you choose whether to display frequencies in Hz or cpm (cycles per minute).

Display Options

  • Show Color Scale
    By default, a vertical color scale is displayed to the right of the spectrogram plot to help provide a proper visual interpretation of spectrogram data. This option allows the color scale to be hidden. When the color scale is visible, manual adjustments to the spectrogram's magnitude scale can be madeusing a two-finger pinch gesture, or single finger slide, within the color scale's label region (as long as Autoscale is turned off).
  • Draw Grid (2D)
    By default, a grid is drawn over the 2D spectrogram to assist with visual identification of time and frequency within the plot. This option allows the grid to be switched off.
  • Apply Smoothing
    This switch enables frequency data to be smoothed into fractional octave bands. Lower frequencies, below the point at which each fractional octave band includes at least one FFT frequency bin, are kept, but not smoothed. Since the full narrowband spectrogram can be very taxing or even overwhelming for the CPU of an iOS device, smoothing is automatically enabled for sample rates of several kHz or more when the spectrogram starts running.
  • Smooth Bandwidth
    Use this segmented control to select the fractional octave bandwidth of the spectral smoothing.
  • Smoothing Type
    Use this segmented control to select the type of spectral smoothing that will be applied.
    • Avg smoothing will simply compute the mean magnitude in each fractional octave frequency band.
    • Max smoothing (selected by default and generally recommended) will pick the highest magnitude within each fractional octave frequency band.
    • In general, Max smoothing works better when peaks are present in the spectrum. Avg smoothing may be suitable when individual spectral peaks are not important.

Cursor Options

  • Peak Track
    The cursor may be configured to automatically move to desired magnitude peaks within the spectrogram. Peaks can be automatically selected either in time for the current frequency, or in frequency for the current time. Selecting Both will cause the cursor to move to the highest value within the entire spectrogram.

3D Plot Options *

  • Plot Type
    Select between 2D and 3D plotting. In 3D mode, the plot can be rotated in 3 dimensions using a typical "trackball" approach, just by sliding a single finger on the screen. 3D mode also offers the following additional plotting options.
  • Draw 3D Axes
    Grid planes for each axis (magnitude vs. frequency, magnitude vs. time, and frequency vs. time) are drawn at the bounds of the 3D plotting region. These grids may be turned off with this switch.
  • Draw Surface
    By default, the 3D spectrogram is drawn as a surface and magnitude values are represented by both position and color. The surface can be turned off, which allows data to be drawn only as a mesh (see below) or for the frequency and time slices associated with the current cursor position to be easily seen.
  • Draw Mesh
    The 3D spectrogram data can be seen as a solid-colored mesh (the mesh draws nothing between its lines or points). The mesh can be overlaid on the surface or drawn alone (by turning the surface off and the mesh on).
  • Mesh Type
    The mesh can be drawn as lines in time, lines in frequency, or lines across both time and frequency. It can alternatively be drawn as a series of dots, each one representing a single spectrogram data point.