A sonogram (also called spectrogram) is a two-dimensional graphical representation of a sound. An example of a sonogram is shown below:
The bottom part of the window contains a waveform representation of the sound, just like in the main document window. The top part represents the frequency as a function of time, with intensities shown with a color scale. With the scale chosen for this picture, the white and yellow parts are of low intensity whereas the red and blue parts are of high intensity.
Basically, each vertical slice
of a sonogram corresponds to
a spectrum analysis as described in the previous section, except that
intensities are displayed with a color scale. When hovering over a
sonogram, the frequency (and nearest note in brackets) corresponding
to the current location of the mouse is displayed in the lower left
corner of the window. A sonogram window can be navigated in pretty
much the same way as a sound document window. Most of the same key
shortcuts work in both windows. The Color palette menu of the
toolbar allows you to choose between different color scales, as well
as to edit them.
The Range and Gain sliders in the toolbar allow to adjust the color scale. Its effect is probably best explained by an example. Let’s say that one chooses the Grayscales color palette which draws areas of low intensity in white and areas of high intensity in black. Then, if Range is set to 60 and Gain is set to 15, every intensity above –15dB will be drawn in black and every intensity below –75dB (75 = 60 + 10) is drawn in white. Intensities falling between these two extreme values will be drawn in shades of gray.
Clicking on the Settings icon in the toolbar shows the following dialog:
The Image size field allows you to choose the height of the sonogram in pixels and the Resolution field allows you to choose its resolution. This latter setting is only used when printing or when exporting the sonogram to an image file. The Frequ. scale field allows you to switch between a linear and a logarithmic scale for frequencies. In a linear scale, the distance between successive harmonics of a given frequency is constant, whereas in a logarithmic scale it is the distance between successive octaves which is constant. The Pixels / semitone setting is only relevant if the frequency scale is chosen to be logarithmic. It allows you to set the distance (in pixels) between two successive semitones on the sonogram. Note that there are 12 semitones in an octave, so that if this value is for example set to 10, then two successive octaves will be 120 pixels apart.
The Max. Frequ. setting allows you to change the maximum
frequency displayed in the sonogram. This is always a subharmonic of the
sampling rate. The FFT size and Window settings have exactly
the same meanings as the Size and Window settings for
the Spectrum function. Note that the FFT size value
does not necessarily need to match the Image size value.
Larger values tend to give a crisper
picture, whereas lower
values will give a more blurred picture. It is usually a good idea to
use some windowing in order to get a nice sonogram representation of a
sound.
Sonograms can be exported as pictures in various formats by choosing Save A Copy As in the File menu. They can also be saved in a format proper to Amadeus Pro by choosing Save in the File menu.
Note: This format is not compatible with sonogram files created by Amadeus II.
