Knowledge Base

Visualize Audio

How Audio Files Are Displayed

Audio files are visualized as waveforms. By default, the waveforms are shown as a line plot. To view the audio data points, choose View Settings > Data Points.

Audio Level

With the volume control in the Playback Control window you can adjust the volume for all media files, and mute/unmute all audio streams. This volume control works independent from the Windows volume control. By default, the volume control is hidden. To show it, choose Setup > Project Settings > Playback Control Options and select Show Volume Control.

Audio Channels

The audio plot shows two channels (left and right) for stereo signals, and one channel for mono signals. If an audio/video file contains more channels, only the first two are visualized. The first audio signal you add to an observation is not muted; additional audio files are muted. This is indicated by the red line through the speaker icon. Click the speaker icon to unmute it.

Audio Values

You can see the value of a data point in the audio plot in one of the following ways:

• Drag the audio plot to the point you require (also using the Playback Control) and check the value next to the video/audio file name. This is the value corresponding to the red hairline.
• With the mouse, hover on a data point. This point becomes bigger and its value appears in a tool tip.

Values are shown in dB (deciBel). These are dBFS, Decibel Full Scale, which is commonly used for digital signals. The average loudness generally determines its overall perceived volume. In the waveform, the level of average loudness appears as the densest, darkest part around the middle. dBFS is calculated as follows:

dBFS = 20 * Log10 (Acur/Amax)

Where:

• Acur = the absolute value at the current time point
• Amax = the maximum possible absolute value. For instance, for 16-bit audio: 2¹⁵ - 1 = 32767
• dBFSmin = 20 * Log10 (0/32767) = -∞ dB (infinite)
• dBFSmax = 20 * Log10 (32767/32767) = 0 dB

0 dB represents the highest possible value. All values below the maximum are negative numbers. For instance, for 16-bit audio the lowest possible value is -96 dBFS.

Notes

• Synchronization between audio from video files and the corresponding video images is within 2 frames (80 ms for PAL, 67 ms for NTSC).
• See Supported Audio Formats for Visualization for the audio formats that can be visualized.
• Audio data are plotted once, even if your Data Profile contains more than one Result container.

Visualize External Data

Prerequisite

Your license includes the External Data Module.

The External Data Plot

External data imported into The Observer XT are shown in line or waveform-like plots. The imported data consist of discrete samples. In the visualization in The Observer XT, the samples are connected by a line, but this does not mean that the data are interpolated and become continuous. To show the individual data points, choose View Settings > Data Points.

External Data Labels

Dependent on the device that collects data, the dataset may not display units or other details on the external data stream. To edit these labels in the visualization, click the label in the external data plot and enter the details in the window that opens.

The fields are also entered in the Independent Variables list. The other way around, if you fill out fields in the Independent Variables list for external data, these are shown in the External Data and Audio plot.

External Data Plots and Data Selection

In the example below, the heart rate of the child was acquired using Polar equipment (sample rate: 0.2 Hz). In a data profile, you select intervals by Polar heart rate higher or equal to 100 bpm.

The sample at time stamp 76.16 s is the first one that is below 100 bpm and therefore the first interval ends at that time. Similarly, the sample at time 87 s is the first one above 100 bpm and therefore the second interval starts at that time. A sample at the exact end of an interval is not included in any statistical analysis.

External Data Plots with Missing Samples

If your imported data contain missing values, these appear as gaps in the visualization.

Notes

• External data streams are plotted once, even if your Data Profile contains more than one Result container.

Visualize Comments

By default, comments are not shown in the event plot. To visualize them, choose View Settings > Show Comments. The comments are now shown in the bars of state events, or next to the point events. If a comment is longer than the bar of the state event, or the space between two point events, only part of the comment is shown. Zoom in to show the full comment.

You can visualize observations when it either contains events (or when the active data profile contains events) or when the observation contains external or audio data. So, when your observation only contains comments but also external data, the observation can be visualized. However, the comments themselves are only visualized when they are scored together with an event.