Tweet
View Histogram vs. Time
(Forensics Version Only)
The histogram (sometimes called a histograph) of an audio signal is a probability distribution of the amplitude density of audio signal data found in a sector of an audio file. The Diamond Cut Histogram vs. Time feature plots this function vs Time. It is normalized so it displays relative frequencies of grouped amplitude occurrences as a function of time. These groups (or bins) have a displayed area which is proportional to the number of certain amplitude events occurring per unit of time. The Histogram vs. Time feature marches through the file and presents a string of histograms to show trends in the file amplitude data distribution throughout the audio file of interest. The Y axis represents counts, while the X-axis represents time. The Z-Axis (color and shade) represents the frequency of occurrence for the scaled (normalized) events. The Histogram vs. Time tool can be useful in the forensics audio authentication process, graphically presenting discontinuities that may be present in a file in question. The routine does not make qualitative determinations, but presents statistical histogram distribution data for interpretation by the examiner. If a bit weight is changed due to an edit in a file, it may show up in “View Histogram vs Time” display, begging further investigation into that region of the sound file.
To create the Histogram vs. Time graph, simply click on the item having that name under the Forensics menu and it will calculate the data and create a display for your inspection. Alternatively, simply click on the histogram icon near the upper right side of the time display. The sliders to the right side of the graphical display can be used to enhance the contrast and/or color of the graph; the leftmost slider affects the chrominance (color saturation) level of the signal and the rightmost control affects the background color of the image. To turn the Histogram vs. Time off, just click on that item again in the Forensics Menu and it will be removed from the display screen.
You can adjust the Histogram vs Time graphic display by right-clicking your mouse on the display. You will see “Edit Histogram Properties” at the top of the list and the following dialog box will appear after left clicking on it:
The Histogram Control Panel
Using this control panel, you can adjust the Histogram Size (per bin). It is advisable to use values greater than 256 bins if you care to resolve the difference between 8 bit, 16 bit and 24 bit file edits. A good starting value is 512 bins. The amplitude axis (Z-Axis) can be set for linear or a variable value of Z-axis Gamma. The Y-Axis range can be used to offset the display to hone in on a certain area of the graph.
Histogram vs. Time Example (bottom trace)
The Histogram vs. Time shown here in the lower trace is taken from the sample file called “Mary had a Histogram” demo file provided with this software. Note the obvious edit shown on the graphical display where an 8 bit edit was performed on a 16 bit file.
(Forensics Version Only)
The histogram (sometimes called a histograph) of an audio signal is a probability distribution of the amplitude density of audio signal data found in a sector of an audio file. The Diamond Cut Histogram vs. Time feature plots this function vs Time. It is normalized so it displays relative frequencies of grouped amplitude occurrences as a function of time. These groups (or bins) have a displayed area which is proportional to the number of certain amplitude events occurring per unit of time. The Histogram vs. Time feature marches through the file and presents a string of histograms to show trends in the file amplitude data distribution throughout the audio file of interest. The Y axis represents counts, while the X-axis represents time. The Z-Axis (color and shade) represents the frequency of occurrence for the scaled (normalized) events. The Histogram vs. Time tool can be useful in the forensics audio authentication process, graphically presenting discontinuities that may be present in a file in question. The routine does not make qualitative determinations, but presents statistical histogram distribution data for interpretation by the examiner. If a bit weight is changed due to an edit in a file, it may show up in “View Histogram vs Time” display, begging further investigation into that region of the sound file.
To create the Histogram vs. Time graph, simply click on the item having that name under the Forensics menu and it will calculate the data and create a display for your inspection. Alternatively, simply click on the histogram icon near the upper right side of the time display. The sliders to the right side of the graphical display can be used to enhance the contrast and/or color of the graph; the leftmost slider affects the chrominance (color saturation) level of the signal and the rightmost control affects the background color of the image. To turn the Histogram vs. Time off, just click on that item again in the Forensics Menu and it will be removed from the display screen.
You can adjust the Histogram vs Time graphic display by right-clicking your mouse on the display. You will see “Edit Histogram Properties” at the top of the list and the following dialog box will appear after left clicking on it:
The Histogram Control Panel
Using this control panel, you can adjust the Histogram Size (per bin). It is advisable to use values greater than 256 bins if you care to resolve the difference between 8 bit, 16 bit and 24 bit file edits. A good starting value is 512 bins. The amplitude axis (Z-Axis) can be set for linear or a variable value of Z-axis Gamma. The Y-Axis range can be used to offset the display to hone in on a certain area of the graph.
Histogram vs. Time Example (bottom trace)
The Histogram vs. Time shown here in the lower trace is taken from the sample file called “Mary had a Histogram” demo file provided with this software. Note the obvious edit shown on the graphical display where an 8 bit edit was performed on a 16 bit file.