Spectrogram

SignalScope offers an FFT-based Spectrogram, capable of displaying magnitude spectra, with any of various data window types and frequency resolutions. Audio input is typically sampled at a rate of 48 kHz, which enables a spectral bandwidth of nominally 24 kHz. The built-in accelerometer supports a bandwidth of approximately 50 Hz.

The available data window types include:

• Uniform (rectangular)
• Bartlett
• Blackman
• Flat Top
• Hamming
• Hann (Hanning)
• Rife-Vincent 2

Frequency resolutions between 1 Hz and 50 Hz may be specified for audio input, depending on the current sample rate. Resolutions between 1 Hz and 10 Hz may be specified for the built-in accelerometer. Finer frequency resolutions yield longer FFT's.

A data cursor may be placed within the spectrogram display with a single tap. You can move the data cursor by sliding your finger to the right or left inside the spectrogram display. When the cursor is visible, spectrum information associated with the cursor is displayed in a small info view above the spectrum display. It is possible to zoom in or out on the spectrum display with a two-finger pinching gesture, and to pan the display, while zoomed in, with two fingers. A double tap resets the display zoom and a second double tap turns off the data cursor.

• In 3D mode, sliding your finger on the spectrogram will cause it to rotate as if in a virtual trackball. A two-finger pinch gesture will move the spectrogram closer or farther in a virtual 3D space. A double tap will reset the rotation and position of the spectrogram surface to its default location. A second double tap will turn off the cursor. You can still place the cursor with a single tap in 3D mode.

Cursor peak tracking can be toggled on and off with a triple tap. In the spectrogram options screen, one of three cursor peak track modes may be selected. 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.

Depending on the current auto-scaling selection, the magnitude scale of the spectrum display may also be manually adjusted by a single-finger slide, or with a two-finger pinching gesture inside the magnitude color scale axis region (the region containing the title and labels). The color scale may also be hidden in the spectrogram options screen to make more room for the spectrogram surface plot.