Sound is a vibrational energy that travels through a medium such as air, water or solid material. It is transmitted in the form of longitudinal waves of varying frequency and amplitude. Speech is a complex sound produced by humans for communication that contains different frequencies important for speech between 100-8000 Hz. Forensic voice identification analyzes the unique characteristics of an individual's voice such as fundamental frequency, intensity, wavelength, intonation and timbre to identify unknown speakers, which has applications for criminal cases where only a recorded voice is available as evidence.

1. FORENSIC PHYSICS
TEJASVI BHATIA

2. What is sound
 Sound is transmitted through a solid, liquid, or
gas; particularly, sound means those vibrations
composed of frequencies capable of being
detected by ears (20Hz to 20KHz).
Sound is a vibrational energy that travels in the
form of signal (carrying information) in medium.

3. Sound Waves
 Longitudinal waves
 Travels through a medium in the form of
compressions and rarefactions.
 Simple and complex
 Complex sound: Periodic, quasi periodic
and non periodic

5. 300 Hz
Sound
500 Hz
Sound
Sound

8. Sound v/s Speech
 All Speech is a sound but all Sound is not a speech
 Speech is a sound which is the form of
communication among human being.
 Speech is a sound wave of air originated from the
complex actions of human body.
 Speech is a complex waveform. It contains
different frequencies.

9. Characteristicsof Sound/Speech/Voice
1. Frequency/Pitch: No of cycles per
second.
100 Hz
200 Hz
1 second

10.  Audible frequency range: 20 Hz to 20 KHz
 Frequencies important to speech signals are in the
range of 100- 8000 Hz.
 Frequency related to the pitch directly.
 When frequency of vibration increased pitch increased
and vice versa.
 Frequency is measurable but Pitch is a psychological
phenomenon.
 Pitch is basically Fundamental Frequency of a person.

11.  Male fundamental frequency/Pitch range : 80-
150 Hz
 Female fundamental frequency/Pitch
range:150-250 Hz
 Child fundamental frequency/Pitch range:
greater than 250 Hz

12. 2. Intensity/ Loudness:
 Amplitude/Energy of signal or Sound
Pressure level.
 Intensity is measurable, Loudness is
psychological phenomenon.
A

13.  More intensity more loudness and vice
versa.
 Unit of intensity is dB (decibel).
 SPL = 20 log 10 (P0/Pr)

14.  Wavelength: Length of complete one wave
λ
= c/fλ

15.  Female’s voice has less wavelength than
male’s voice because female’s fundamental
frequency is more than male’s
fundamental frequency.

16.  Intonation: Variation in pitch pattern.
 Voice Quality/ Timbre: like Breathy Voice
 Diction: Clarity of speech
 Resonance: Human organ pipe is one end closed pipe
First Harmonic/Formant f1 = λ/4
Second Harmonic/formant f2 = 3λ/4
Third Harmonic/formant f3 =5λ/4 ………
Only odd Harmonics

18. VOICE IDENTIFICATION

19. Voice Identification is one of the important
emerging areas in forensic science
The recent development in the area of
information and communication technology has
made infinite advantage of connecting people
over exceptionally large distance at the fraction
of second - The brighter side of the coin.

20. But the darker side of the coin flashes the
use of communication technology in
several criminal offences such making
hoax calls to the police, ambulance or fire
brigade, making threatening or harassing
telephone calls, blackmail or extortion
demands or match fixing etc.

21.  Developed in the early years of 1940’s by
Green, Potter and Kopp at the Bell
Laboratories for the purpose of helping
military during world war II

22.  After criminal offence, no evidence
was left except the recorded
voice/voices of the suspect/suspects
then we definitely need for
Voice/Speaker Identification.

23. Voice Identification
 The task of determining an unknown
speaker’s identity. (Voice identification
determines which registered speaker
provides a given utterance from
amongst a set of known speakers.)
 Person’s speech/voice characteristics

24. MethodsofVoice/speakeridentification
 Aural examination of voice
 Spectrographic - visual examination
of voice spectrogram
 Automatic method of voice
identification