Tag Archives: Forensic investigation


By @forensicfield

This is as a kind of a quick-reference list for important technical terms from Forensic Speaker Identification.

Which is taken from –


The pronunciation used by a speaker (as opposed to other things like choice of words or syntax) that is characteristic of a particular area, or social group.

Acoustic Forensic Analysis

The expert use of acoustic, as opposed to auditory, information to compare forensic speech samples.

Acoustic Phonetics Or Speech Acoustics

That part of phonetics that deals with the properties of speech sounds, and how they are transmitted between speaker and hearer.


The realisation of a morpheme. Two allomorphs of the plural morpheme in English for example are s, as in gnats and es as in horses.


A speech sound functioning as the realization of a phoneme.

Articulation Rate

A measure of how fast someone speaks, usually quantified in terms of syllables per second, exclusive of pauses.

Articulatory Phonetics

The study of how speech sounds are made by the speaker.

Auditory Forensic Analysis Or Technical Speaker Recognition By Listening

The expert use of auditory, as opposed to acoustic, information to compare forensic speech samples.

Aural-spectrographic Identification

Highly controversial method of speaker identification using both visual examination of spectrograms and listening.

Between-speaker Variation

The fact that different speakers of the same language differ in some aspects of their speech. One of the conditions that makes forensic speaker identification possible.

Centisecond or csec or cs

Unit for quantifying duration in acoustic phonetics: one hundredth of a second.


A very common parameter used in automatic speaker recognition, one effect of which is to smooth the spectrum.

Closed Set Comparison

An unusual situation in forensic speaker identification where it is known that the offender is present among the suspects.


The tendency for two participants in a conversation to become more similar in their speech behaviour to signal in-group membership. Speakers can also diverge from one another.

Conversation analysis

The study of how conversation is structured and regulated.

Decibel or dB

Unit for quantifying amplitude in acoustic phonetics.


The study of how language varies with geographical location.


The process of converting an analogue speech signal, e.g. from a cassette recorder, into a digital form that can be used by a computer for speech analysis.


A vowel in a single syllable that involves a change in quality from one target to another, as in how, or high.

F– (Or Formant) Pattern

The ensemble of formant frequencies in a given sound or word.

False Negative

In speaker recognition, deciding that two speech samples have come from different speakers when in fact they are from the same speaker.

False Positive

In speaker recognition, deciding that two speech samples have come from the same speaker when in fact they are from different speakers.

FFT or Fast Fourier Transform

A common method of spectral analysis in acoustic phonetics.


A very important acoustic parameter in forensic speaker identification. Formants reflect the size and shape of the speaker’s vocal tract.

Formant Bandwidth

An acoustic parameter that reflects the degree to which acoustic energy is absorbed in the vocal tract during speech.

Fundamental Frequency (Or F0)

A very important acoustic parameter in forensic speaker identification. F0 is the acoustic correlate of the rate of vibration of the vocal cords.

Hertz (or Hz)

Unit for quantifying frequency: so many times per second. 100 Hz for example means one hundred times per second.

Incidential Difference

One of the ways in which speakers can differ in their phonemic structure.

Indexical Information

Information in speech that signals the speaker as belonging to a particular group, e.g. male, middle-class, with a cold, Vietnamese immigrant, and so on.


The use of pitch to signal things like questions or statements, or the emotional attitude of the speaker.

Kilohertz (or kHz)

Unit for quantifying frequency: so many thousand times per second. 1 kHz for example means one thousand times per second.

Linear Prediction

A commonly used method of digital speech analysis.


A common type of quantification in forensic speaker identification whereby a parameter, usually fundamental frequency, is measured over a long stretch of speech rather than a single speech sound or word.

Manner (of articulation)

The type of obstruction in the vocal tract used in making a consonant, e.g. fricative, or stop.

Millisecond (or msec or ms)

Common unit for quantifying duration in acoustic phonetics: one-thousandth of a second.


A unit of linguistic analysis used in describing the structure of words: the smallest meaningful unit in a language. For example, the word dogs consists of two morphemes: {dog} and {plural}.

Naive Speaker Recognition

When an untrained listener attempts to recognize a speaker, as in voice line-ups, etc.

Open Set Comparison

The usual situation in forensic speaker identification where it is not known whether the offender is present among the suspects.

Parameter (Or Dimension, Or Feature)

A generic term for anything used to compare forensic speech samples, e.g. mean fundamental frequency, articulation rate, phonation type.

Phonation Type

The way the vocal cords vibrate, giving rise to auditorily different qualities, e.g. creaky voice, or breathy voice.


A technical name for speech sound.


A unit of linguistic analysis: the name for a contrastive sound in a language. For example, bat and pat begin with two different phonemes.


The study of how speech sounds function contrastively, to distinguish words in a given language. Phonemics is an important conceptual framework for the comparison of forensic speech samples.

Phonetic Quality

One of two very important descriptive components of a voice, the other being voice quality. Describes those aspects of a voice that have to do with the realisation of speech sounds.


The study of all aspects of speech, but especially how speech sounds are made, their acoustic properties, and how the acoustic properties of speech sounds are perceived as speech by listeners.


One of the main sub-areas in linguistics. Phonology studies the function and organisation of speech sounds, both within a particular language, and in languages in general.


  • An important auditory property of speech.
  • Pitch and pitch range can be used to characterise an individual’s voice.
  • Another term for fundamental frequency.

Pitch Accent

The use of pitch to signal differences between words that is partly like tone and partly like stress. Japanese is a pitch-accent language.

Place (of articulation)

Where in the vocal tract a consonantal sound is made.

Posterior Odds

In forensic speaker identification, the odds in favour of the hypothesis of common origin for two or more speech samples after the forensic-phonetic evidence, in the form of the likelihood ratio, is taken into account. The posterior odds are the product of prior odds and LR.

Prior Odds

In forensic speaker identification, the odds in favour of the hypothesis of common origin for two or more speech samples before the forensic-phonetic evidence is taken into account.

Realisational Difference

One of the ways in which speakers can differ in their phonemic structure.


A generic term for vowels and consonants.


A way of talking that is typical of a particular social group.


The study of how language varies with sociological variables like age, sex, income, education, etc.

Spectral Slope

An acoustic parameter that relates to the way the vocal cords vibrate.


A picture of the distribution of acoustic energy in speech. It normally shows how frequency varies with time. Spectrograms are often used to illustrate an acoustic feature or features of importance.

Speech Perception

That part of phonetics that studies how the acoustic properties of speech sounds are perceived by the listener.


The result of an acoustic analysis showing how much energy is present at what frequencies in a given amount of speech.

Standard Deviation

A statistical measure quantifying the spread of a variable around a mean value.


Prominence of one syllable in a word used to signal linguistic information, like the difference between implant (noun) and implant (verb) in English.

Subglottal Resonance

A frequency in speech attributable to structures below the vocal cords, e.g. the trachea.


A generic term for tone, stress and intonation.

Syllable (Or Speaking) Rate

A measure of how fast someone speaks, usually quantified in terms of syllables per second, inclusive of pauses.

Systemic Difference

One of the ways in which speakers can differ in their phonemic structure.


The use of pitch to signal different words, as in tone languages like Chinese.


A statistical measure quantifying the variability of a variable; the square of the standard deviation.

Voice Quality

One of two very important descriptive components of a voice, the other being phonetic quality. Describes those long-term or short-term aspects of a voice that do not have to do with the realisation of speech sounds.

Voiceprint Identification

Highly controversial method of speaker identification exclusively using visual examination of spectrograms.

Voice Print

Another name for spectrogram. Usually avoided because of its association with voice print identification.

Voicing / Phonation

Refers to activity of the vocal cords.

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Laws and Principles of Forensic Science

Sources:A Closer Look On Forensic Science written by Archana Singh


Forensic Science is the science which has developed its own Laws and Principles. The Laws and Principles of all the natural sciences are the bases of Forensic Science.

Every object, natural or man-made, has an individuality which is not duplicated in any other object.

1. Law of Individuality

Anything and everything involved in a crime, has an individuality. If the same is established, it connects the crime and the criminal.

This principle at first sight appears to be contrary to common beliefs and observations. The grains of sand or common salt, seeds of plants or twins look exactly alike.

2. Principle of exchange

Contact exchange traces is principle of exchange. It was first enunciated by the French scientist, Edmond Locard. Commonly known as Edmond Locard’s maxim on Interchange.

According to the principle, when a criminal or his instruments of crime come in contact with the victim or the objects surrounding him, they leave traces. Likewise, the criminal or his instruments pick up traces from the same contact.

3. Law of progressive change

“Change is inevitable” , this also applies to object. Different types of objects may take different time spans.

The criminal undergoes progressive changes. If he is not apprehended in time, he becomes unrecognizable.

The scene of occurrence undergoes rapid changes. The weather, the vegetable growth, and the living beings make extensive changes in comparatively short periods.

Samples degrade with time, Bodies decompose, tire tracks & bite marks fade, the firearm barrel loosen, metal objects rust, etc.

4. Principle of comparison

“Only the likes can be compared” is the principle of comparison.

It emphasize the necessity of providing like samples and specimens for comparisons with the questioned items.

A questioned hair can only be compared to another hair sample, same with tool marks, bite marks, tire marks, etc.

For example

A specimen obtained by writing on the same wall, at the same height and with the same instrument and then photographed. It can be matched.

Once handwriting available on a photograph allegedly written on a wall was compared with the specimen written on paper. It did not give worthwhile results.

5. Principle of analysis

The Analysis can be no better than the sample analyzed.

Improper sampling and contamination render the best analysis useless.

The principle emphasizes the necessity of correct sampling and correct packing for effective use of experts.

6. Law of probability

All identification, definite or indefinite, are made, consciously or unconsciously, on the basis of probability.

Probability is mostly misunderstood. If we say that according to probability a particular fingerprint has come from the given source, but it is not a definite opinion.

Probability is a mathematical concept. It determines the chances of occurrence of a particular event in a particular way.

If “P” represents probability, “Ns” the number of ways in which the event can successfully occur (with equal facility) and “Nf” the number of ways in which it can fail ( with equal facility) , the probability of success is given by the formula:

7. Law Of Circumstantial Facts

“facts do not lie, men can and do”

Evidences given by eye witnesses or victims may not always be accurate.

Sometimes victims may intentionally lie or sometimes because of poor senses (such as low sight, unclear hearing), exaggeration & assumptions.

According to Karl Marx “True belief only becomes knowledge when backed by some kind of investigation and evidence”.

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Laws & Principles of Forensic Science

Know More Details of Laws and Principles of Forensic Science; Read

“A Closer Look On Forensic Science”

Forensic Science

Sources:A Closer Look On Forensic Science written by Archana Singh

What is Forensic Science?

• Forensic science is the study and application of science to matters of law.
• Forensic Science (or Criminalistics) is the use of science & technology to enforce civil & criminal laws.
• It is vast & hard to define because it includes so many other areas of science.


Forensic science has developed over the past 300 years or so, and its processes continue to improve and evolve today as science and technology find better and more accurate techniques. In 1929 the first American forensic lab was created in Los Angeles by the police department.

Where and when is forensics used?

These days forensic science is used to investigate nearly all crime scenes. With the advancements of science, most forensic science techniques are a common and necessary part of a criminal investigation.

Why is it important?

There has always been a role for forensic science in criminal investigations, but with criminals committing clever, well thought out crimes more often, forensic science is now an essential tool for criminal investigations.

What skills are involved in forensic science?

Forensic science uses a lot of different skills. These include:

🔎 Observational skills – to be able to find and compare evidence. To be able to discover things the untrained eye may miss.
🔎 Evidence collection and analysis – this is vital to the role of a forensic scientist. Evidence that is collected needs to be well documented and it is crucial that contamination of evidence does not occur. To collect evidence a forensic scientist needs to be methodical and accurate.
🔎 Scepticism – healthy scepticism is an important part of investigating crimes. Everyone is a suspect until something concrete proves otherwise. It is also important to understand that witness accounts aren’t always very accurate. It has been found that when referring to memories (such as during a witness account) most people have trouble getting all details correct and most people’s perceptions are based on their personal lives and values.

Tool kit for a forensic scientist

Those forensic scientists required to find, collect, protect and transport evidence from the crime scene require a kit of tools to use. Although each forensic scientist may do things a little differently, there are typical tools that they all use. These are:

✴ Crime scene tape to secure the scene and the are around which the crime took place.
✴ Camera and film to photograph scene and evidence.
✴ Gauges to place in photos to allow for recording of scale.
✴ Sketchpad and pens for scene sketches.
✴ Disposable and protective clothing (overall suits), face masks and gloves (usually latex gloves).
✴ Torch and other light sources such as laser, ultra violet (UV) and infrared (IR) lighting. These different lights can uncover certain types of evidence that normal torchlight won’t.
✴ Magnifying glass to help with finding trace evidence.
✴ Tweezers for collecting evidence such as hair and fibres.
✴ Cotton wool buds (cotton swabs) for collecting samples of fluid evidence.
✴ Evidence bags (paper and plastic) and evidence tubes (plastic and glass) and marker pen to label evidence. This assists in keeping evidence uncontaminated and allows for safe and easy transport to the lab.
✴ Fingerprint supplies this includes things like ink, print cards, lifting tape, dusting powders (there are a variety of these for different situations) and exposing reagents (such as luminol).
✴ Casting kits for making casts of shoe/footwear prints, animal prints, tyres and tool markings.

Crime scene procedures

When investigators attend a crime scene, generally these procedure is as follows:

Preserving life – whatever the type of crime scene. The first priority is to preserve life and assist any victims if they are injured.

Suspects at the scene – suspects should be detained and removed from the scene. This also allows for searches, statements and behaviour to be documented.

Controlling the scene – the more people who come in contact or visit the crime scene, the more difficult it is to keep the site uncontaminated and for investigators to collect evidence.

Reel Vs. Reality

While on TV shows such as CSI, where Forensic Investigators are seen interviewing witnesses, in “real” life, Forensic Investigators have no contact with witnesses, suspects or others. The role of Forensic Investigators is purely collection and analysis of evidence. It is up to the police to interview and put the pieces of the crime together.

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Basic Forensic Science info

Know About Forensic Science Basics, History and much more in Detail; Read

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Investigation of crime Scene

Sources:A Closer Look On Forensic Science written by Archana Singh

How is it possible to identify the person who committed a crime??

A little amount of blood or a hair or a fiber or a part of skin or any number of different type of materials can help a crime to be reconstructed and lead investigators to the responsible person.

The goal of a crime-scene investigation is to recognize, document and collect evidence at the scene of a crime.

Solving the crime will then depend on putting together the evidence to form a picture of what happened at the crime-scene.

Investigative Process are to:
👉 Establish that a crime was actually committed,
👉 Identify and apprehend the suspect,
👉 Recover stolen property,
👉 Assist in the prosecution of the person,
Charged with the crime.

An investigator is one who collects, documents and evaluates evidence and information. The whole process complete through the investigation.

The purpose of criminal investigation and forensic science is to discover the truth behind the scene.

🔗 The initial Boundary established around the crime scene should be larger than the scene.
🔗 This boundary can easily be shifted inward later but is not as easily enlarged because the surroundings areas may have been contaminated during ensuring interval.
🔗 The Responding officers must document all actions and observations at the scene as soon as possible.

🧤 Naturally, a general rule of protecting the crime scene cannot be applied in every case.
🧤 Who arrive first at crime scene referred as first officer or first responder. The first officer’s top priority to offer assistance for any injured person.
🧤To safeguards evidence and minimize contamination , access to scene must be limited and any persons found at the scene must be identified , documented and then removed from the scene.
🧤 As additional officers arrive, they will begin procedures to isolate the area, using barricades and police tape unauthorized persons from the scene.

Documenting of the crime scene and the evidence involve four major task:
1. Note-taking
2. Photography
3. Sketching
4. Videography

The lead investigators first task is to evaluate the scene should be processed for physical evidence.
 The collection and analysis be processed for physical evidence.
 The lead investigator will direct and control the processing. Starting with the recognition of physical evidence.


Pattern of search at crime – scene.
For the search of crime scene following search patterns are use.

Once the discoverer, time of discovery location and appearance of evidence have been thoroughly documented, the evidence must be collected, preserved, inventoried, and packaged in preparation for submission to the forensic lab.

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