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High-Definition Spectrogram
(Forensics Version Only)
The DC Forensics10 Audio Laboratory version includes a very High Definition Spectrogram which allows for FFT Sizes up to 131,072 (65,536 Frequency Bands). It also includes Decimation techniques to further optimize for higher Frequency Resolution as well as Zero-Pad techniques in order to optimize for better Time Interval Resolution. Both the frequency and time resolution parameters have been integrated into one simple and easy to use “Increase Resolution” slider control. Additionally, you can choose between several window techniques depending upon your specific needs. The overall combination of features makes the High Definition Spectrogram well suited to identify tape dubs based on multiple line frequency pickup signals. It is also useful for identifying edit points in forensics audio files. And, it provides an exceptional voice print display for detailed comparison between known and unknown voice sources. The High Resolution Spectrogram dialog box is pictured below:
The High Definition Spectrogram Dialog Box
Most of the functionality of the High Definition Spectrogram is the same as that of the Standard Definition version with the following exceptions:
Note 1: The High Definition Spectrogram responds to the channel selected. When both channels are selected, it responds to the sum of the two.
Note 2: The Spectrogram Dialog Box can be accessed by either double-left mouse clicking on the spectrogram display itself or via the Preferences Menu found under “Edit”.
There is an example of an edited .mp3 file using 5 different bit rates ranging from 224k to 192k to 128k to 48k and finally to 8k. Note the obvious edit points in the file as seen on the high resolution spectrogram (note that this audio file is included with this software as a demo and is titled “Edited Composite bit rate mp3 file.wav”):
Edited File with varying bit rates shown in sync with hi-res spectrogram
(Forensics Version Only)
The DC Forensics10 Audio Laboratory version includes a very High Definition Spectrogram which allows for FFT Sizes up to 131,072 (65,536 Frequency Bands). It also includes Decimation techniques to further optimize for higher Frequency Resolution as well as Zero-Pad techniques in order to optimize for better Time Interval Resolution. Both the frequency and time resolution parameters have been integrated into one simple and easy to use “Increase Resolution” slider control. Additionally, you can choose between several window techniques depending upon your specific needs. The overall combination of features makes the High Definition Spectrogram well suited to identify tape dubs based on multiple line frequency pickup signals. It is also useful for identifying edit points in forensics audio files. And, it provides an exceptional voice print display for detailed comparison between known and unknown voice sources. The High Resolution Spectrogram dialog box is pictured below:
The High Definition Spectrogram Dialog Box
Most of the functionality of the High Definition Spectrogram is the same as that of the Standard Definition version with the following exceptions:
- FFT Size: User Adjustable from 32 to 131,072
- Window Choices: Select between Bessel, Blackman, Hamming, Hanning, Kaiser 10, Kaiser 15, Kaiser 20, Rectangular, Triangular and Welch.
- Increase Resolution Control: Moving the slider to the left increases the spectrograms Frequency resolution with the reduction of time resolution (by Decimation) while moving the slider to the right increases the spectrograms Time Interval resolution (by Zero Padding) with a loss of frequency resolution. You make the tradeoff that you require using the Increase Resolution Control. The Decimation and Zero Padding values are annotated just to the right hand side of the slider control. In the middle slider position, neither Decimation or Zero Padding are applied to the system.
- Point and Click Measurement: You can point your mouse to any point on the High Definition Spectrogram and single- left click it and it will display the Frequency in Hz and the Amplitude in dB at that location. The exact measurement location is indicated by a small crosshatch (+) sign on the graphical display adjacent to the numeric display.
- Presets: Several factory presets are provided with the software. You can also add your own favorite presets by using the Save command button found in the Spectrogram dialog box. The delete button is used to eliminate unwanted presets from the preset listing.
Note 1: The High Definition Spectrogram responds to the channel selected. When both channels are selected, it responds to the sum of the two.
Note 2: The Spectrogram Dialog Box can be accessed by either double-left mouse clicking on the spectrogram display itself or via the Preferences Menu found under “Edit”.
There is an example of an edited .mp3 file using 5 different bit rates ranging from 224k to 192k to 128k to 48k and finally to 8k. Note the obvious edit points in the file as seen on the high resolution spectrogram (note that this audio file is included with this software as a demo and is titled “Edited Composite bit rate mp3 file.wav”):
Edited File with varying bit rates shown in sync with hi-res spectrogram