Sound Spectrograph
Definition
An instrument that plots the frequency content of a speech signal over time, with frequency on the vertical axis, time on the horizontal, and acoustic energy represented by trace darkness. Developed at Bell Labs in the 1940s; the visual output is a spectrogram.
- Function
- Plots frequency content of a speech signal over time
- Axes
- Frequency vertical, time horizontal, energy shown as trace darkness
- Origin
- Developed at Bell Labs in the 1940s
- Output
- A spectrogram
Common questions
How does the sound spectrograph relate to the discredited voiceprint identification method?+
The instrument itself is a legitimate acoustic analysis tool still used in phonetics and speech science, but the 1960s-70s claim that spectrograms could be matched like fingerprints to identify speakers with certainty was later shown to lack scientific support, which is why voiceprint identification as originally practised was rejected by courts and scientific bodies.
What can a sound spectrograph reliably show that supports modern forensic phonetics?+
It reliably visualises formant frequencies, pitch contours and voicing patterns over time, which trained phoneticians use alongside acoustic measurements and statistical comparison methods, rather than relying on visual pattern matching of the spectrogram image alone.
Related terms
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- ENFSI BPM
- The ENFSI Best Practice Manual for Forensic Comparison of Speech (2015, rev. 2022); the operational standard for speaker comparison in European forensic...
- Formant
- A resonance peak in the vocal tract filter; F1 and F2 together characterise vowel quality (height and frontness), while F3 and higher...
- Frye Standard
- The US legal test for admissibility of scientific evidence, originating from Frye v. United States (1923), which required that a technique be...
- IAVI (International Association of Voice Identification)
- Organisation founded by Kersta in the late 1960s to train and certify forensic voice identification examiners in the spectrographic comparison method. Certification...
- Likelihood Ratio (LR)
- The ratio of two conditional probabilities: the probability of the observed evidence given the prosecution's hypothesis (same source), divided by the probability...
- NAS 1979 Report
- The National Academy of Sciences report 'On the Theory and Practice of Voice Identification,' which concluded that spectrographic voice identification lacked the...
- Proficiency Testing
- An external quality assurance programme in which a laboratory analyses blind samples distributed by an independent provider and submits results for comparison...
- Voiceprint
- Lawrence Kersta's 1962 term for the claim that the spectrographic pattern of an individual's speech is unique enough to serve as a...