3D Visualization of the Voice Spectrogram Improves Forensic Analysis
The forensic discipline that studies audio takes a leap forward by representing the vocal signal as a three-dimensional relief. This technique processes the sound to generate a model with three axes: time, frequency, and amplitude. In this way, the expert can examine the unique topography of the voice, where elements such as formants and timbre are projected as peaks and depressions. This perspective overcomes the limitation of the classic 2D spectrogram, which condenses intensity data into a simple color scale. 🗣️
Building the Three-Dimensional Model of a Voice
The technical process to create this 3D model begins by extracting the audio signal, for example, from a threatening call and a controlled sample from a suspect. Tools like Python with the Librosa library or Praat software perform the Short-Time Fourier Transform. This analysis generates the raw spectral data. Subsequently, applications like MATLAB or ParaView import this data in matrix format. A specific script converts each point, defined by its time, frequency, and amplitude, into a spatial coordinate, shaping a mesh or point cloud that the analyst can rotate and section.
Key steps in model generation:- Extract and isolate the relevant audio signals for the case.
- Apply spectral analysis (STFT) to decompose the signal into its frequency components over time.
- Translate numerical data into a set of three-dimensional coordinates (X, Y, Z).
- Render the resulting geometry as a solid surface or interactive point cloud.
“Even if a suspect tries to disguise their voice, the personal vocal landscape, that unique orography of their vocal tract, is much harder to completely flatten.”
Comparing Vocal Evidence in 3D Space
Forensic comparison gains precision by observing the complete structure in three dimensions. The expert aligns the two 3D models and looks for matches in the morphology of formants, the slope of the intonation curve, and global energy patterns. A whisper or glottal strike leaves a distinctive mark on this acoustic relief. 3D visualization allows precise measurement of distances and volumes between spectral peaks, providing quantitative and objective metrics for a more robust and harder-to-refute forensic report.
Advantages of 3D comparison:- Inspect the complete structure of the voice, not just a flat projection.
- Measure precisely distances between formants and energy volume in specific bands.
- Identify unique artifacts such as microtremors, whispers, or glottal strikes that have a characteristic spatial signature.
- Provide tangible visual evidence and objective metrics for the courts.
The Future of Acoustic Expert Evidence
This methodology transforms how vocal evidence is analyzed and presented. By moving from a flat representation to a spatial model that can be manipulated, the expert is equipped with a powerful tool to discern the truth. The three-dimensional vocal footprint is posited as a stronger piece of evidence, difficult to completely mask even with distortion techniques, because it captures the physical essence of sound production in the vocal tract. 🔍