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RavenViewer Details

What is Sound Visualization?

Waveforms: Sounds can only propagate in a medium such as air, water, or solids. When no sound is present, the molecules in the medium all experience the same average pressure. When a sound is created, successive peaks of higher than normal pressure and valleys of lower than normal pressure radiate away from the sound source as waves. A microphone can pick up these passing waves and convert them into an electrical recording of the sound. A graph of how a passing sound varied the pressure in front of the microphone over time is called the waveform of that sound. To the right is an example of the waveform of a wild Mitred Parakeet's call.

The horizontal dashed line is the average pressure in the medium outside the microphone when no sound is present. The height of the peaks and valleys around this line indicates the amplitude of the sound: higher peaks and lower valleys will be heard as a louder sound.

Spectrograms: The waveform of the parakeet's call is not steady: successive peaks and valleys have different amplitudes, and some waves are narrower while others are wider. This means that the parakeet's call consists of many different sound frequencies. We can decompose any sound waveform into its component pure frequency components. A graph of the frequency composition of a sound (vertical axis) over time (horizontal axis) is called a spectrogram: Here we can see three successive calls of the parakeet. Each one consists of a stack of different sound frequencies. The contrast of the color against the background indicates the amplitude of each frequency at each instant. Thus the fifth frequency component in these stacks (counting from the bottom) has a greater amplitude than the first component.

Power Spectra: A power spectrum is simply a vertical slice through a spectrogram. The vertical white line in RavenViewer indicates which part of a sound is currently being played. It also determines which vertical slice will be shown in a power spectrum of that sound. To the right is a power spectrum slice through the parakeet's call, where the vertical white line is drawn. The power spectrum slice is rotated clockwise so that the frequency is now on the horizontal axis, and the amplitude of each frequency component in that slice is on the vertical axis. We can see that the fifth component in this slice does in fact have the greatest amplitude.

Download our Sound Analysis Primer to read more about sound visualization.

Adjusting the Settings in RavenViewer

You can customize each of the three views by changing the RavenViewer settings. To change the settings for a particular view, select the appropriate tab at the bottom of the RavenViewer window.

Navigation

Playback Controls: The five buttons below the views provide the main controls for playback: Beginning = move play head to beginning of recording; Rewind = move backwards slowly without playing; Play = play the sound; Stop = stop playback at the current point; Fast Forward = move forwards in the clip quickly without playing it.
Playhead: The playhead is shown as a vertical line in the waveform and spectrogram views. It indicates the part of the sound clip that is currently being played.
Playback Slider: The playback slider (located between the control buttons and the views) can be used to move the playback head over any part of the sound. Subsequent playback will now begin at this selected location.
Location Clicking: Clicking the cursor anywhere inside the waveform or spectrogram views will move the playhead to that location. This works whether the sound is being played or is currently stopped. This is very useful for examining a particular part of a sound clip.

Shared Settings (at top right of window)

Loop: When set to OFF, the sound will play only once and stop. If set to ON, the entire clip will play and then automatically restart at the beginning.
Speed: This is normally set to 1X. Moving the setting to a lower value will play the sound back at a slower speed (e.g. setting it to 0.5X will play the sound back at half speed). Birds can often hear rapid temporal patterns that humans cannot: slowing down the playback of a sound can reveal many subtle details not heard at normal speed. Similarly, very slow sounds can be sped up to get through a playback faster.
Timeline Zoom: This setting sets the scale for the time axis in both the waveform and spectrogram views. A low setting scrunches the recording along the time axis, and a high setting spreads it out.
Cursor Readings:

Time: Moving the cursor along the time axis in the waveform or spectrogram views will show "Mouse Time" and which channel is being examined (if it is a stereo recording) as the time in hours:minutes:seconds for that point relative to the beginning of the recording. You do not need to click to get this reading.

Frequency: Moving the cursor anywhere inside a spectrogram view will post the frequency and channel viewed at the current cursor point. Do not click--just move the cursor to the location of interest.

Waveform Settings

Amplitude: The amplitude slider allows you to adjust the size of the waveform image within its window. An ideal setting would be just enough so that the entire waveform just fits in the display area. The amplitude slider uses a logarithmic scale.
Averaging: When the time scale of the waveform view is compressed, (the most common situation), many successive waves will be represented by a single vertical line in the waveform image. Setting waveform averaging to ON produces waveform images in which a vertical line composed of successive waves at consistently higher amplitude will be shown at greater contrast against the background than one in which the amplitudes of successive waves are not consistently high. The default setting of OFF draws all lines in the waveform at the same contrast against the background.
Color: As with the other views, users have a choice of several different waveform and background color combinations. Choose the one that works best for you.
Enable: As with the other views, choosing SHOW makes this view visible whereas HIDE does not. If you want a larger image for your waveform view, hide the spectrogram and power spectrum views.

Spectrogram Settings

FFT Size: (Fast Fourier Transform) This setting determines the time and frequency resolution of the spectrogram by determining the size of successive segments of the sound that are broken into their frequency components. Longer segments (e.g. larger FFT sizes) improve the accuracy with which the frequency of each component can be determined. However, this reduces the ability to track rapid temporal changes in the sound. Shorter segments (small FFT sizes) provide better temporal tracking, but result in sloppier estimates of the frequency of each component. The optimal setting is usually an intermediate FFT size. It is often useful to stop playback with a typical part of the sound at the playback head. Then try several different FFT sizes. The one that shows the frequency components (as in the Mitred Parakeet example above) as clear thin lines without fuzzing up the separate calls is usually the best setting. This will differ for different species. Experiment!

Download our Sound Analysis Primer to read more about FFT Size.

Power Spectrum Settings

Choosing sample site: The power spectrum shows the component frequencies and their relative amplitudes for a small segment of the sound clip that is currently centered around the playhead. You can see how the power spectrum changes in a sound by clicking in the waveform or spectrogram window in small increments to move the playhead in tiny steps.
Average: When ON, this control produces a running average of successive power spectra as well as the instantaneous spectra as a sound is played. For static examination of a sound's power spectra, it is better to turn this control OFF.
Color: As with other views, users have a number of different color schemes to choose from.
Fill: Most users will want this control turned ON. However, the option to see only the graph of the amplitudes vs frequency of components is available.
Scale: Most users examining bird or mammal sounds will want to set the frequency scale for the power spectra to LINEAR. This means that the interval between adjacent frequencies is the same along the horizontal axis of the view. However, those studying whale sounds may want to set the scale to LOGARITHM which expands the lower end of the frequency scale but still lets the upper end be present albeit compressed.
XScale: This slider "stretches" the frequency (horizontal) axis in the power spectrum view. If the frequencies of interest are not low frequencies, this stretching may move them out of the view. To bring them back into view, use the next control, the XOffset, to change which part of the frequency axis is seen in the view window.
XOffset: This control slides the fraction of the frequency scale which is visible in the power spectrum window back and forth. It only changes the view if the XScale control is set to a value other than zero.
YScale: This control "stretches" the amplitude (vertical) axis in the power spectrum view. For many bird recordings, the default value of zero is too low. An intermediate value of 20-40 may be necessary to get a good sense of how the components of the bird's song vary in amplitude. Changing the YScale usually requires a concurrent adjustment of the YOffset so that just the amplitude peaks of interest are visible above the bottom of the graph.
YOffset: This slider moves the range of amplitude of components visible in the power spectrum view up and down. Since every recording has noise in it, moving this slider too high simply fills the window with the ambient noise variations. Moving it too low hides the peaks of interest. Note that this is the only offset control in RavenViewer that works even if the associated scale setting (here YScale) is equal to zero.
Enable: As with the other views, selecting HIDE removes the power spectrum view from the window, whereas selecting SHOW makes it visible.

Audio Settings

Balance: This slider adjusts the relative loudness of the playback's two channels into the user's speakers or earphones. If the recording is stereo, this will alter the relative amplitudes of the two channels. If the recording is mono, this will simply change the relative amplitudes at which the single channel is played into the two earphones/speakers. Adjusting this slider does NOT change the amplitude of the waveform displays for the two channels; it only changes what is heard by the user.
Bass: This control can be used to reduce the lower frequency content of what is heard during playback from the default of 100% to a very low value. It does not affect the spectrogram or waveform views.
Channels: For a stereo recording, the central position of this slider ensures that both channels will be heard during playback and the selected views for both channels will be visible in the viewer window. Moving it to the left will play back and show the views for the left channel only; moving it to the right will play back and display views for the right channel only. For a mono recording, leaving the slider in the left or central positions will ensure that any selected views are visible. Moving the slider to the right will hide all selected views.
Treble: This control can be used to reduce the higher frequency content of what is heard during playback from the default of 100% to a very low value. It does not affect the spectrogram or waveform views.
Volume: This slider can be used to reduce the amplitude of the playback in the user's speakers or earphones. It does not affect any of the views of the sound.

Video Settings

Enable: Selecting HIDE will remove the video playback from the viewer window. Selecting SHOW will make the video playback visible.

CatalogRecord

This tab will list some of the metadata associated with the currently selected sound or video clip.

Media

This tab lists the format in which the original recording was made and various parameters about the original recording.

Display

Playhead Color: This slider lets the user select the color for the playhead line. By choosing the current background color, this can be used to hide the playhead.