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.
Data 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.
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.
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).
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.
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.