The CD said to have contained the recordings of the conversation between Shanti Bhushan and Mulayam singh had been examined forensically. The Central Forensic Science Laboratory seems to have opined that the CD is not doctored while the Hyderabad Truth Labs had said it is fabricated. Now Chandigarh FSL is said to have opined that the CD was a ‘cut and paste’ job.
In as much as the recordings in a CD can only be a secondary recording which will always contain the inherent defects editing, volume management, suppression of noise etc the finding that the CD is doctored or fabricated or cut and paste job has no forensic evidentiary value.
What is important in this case is the speaker verification [or speaker authentication] and identification. Speaker recognition uses the acoustic features of speech that have been found to differ between individuals. These acoustic patterns reflect both anatomy , namely size and shape of the throat and mouth and learned behavioural patterns, namely voice pitch, speaking style. Speaker verification has earned speaker recognition its classification as a "behavioural biometric."
There are two major applications of speaker recognition technologies and methodologies. If the speaker claims to be of a certain identity and the voice is used to verify this claim, this is called verification or authentication. On the other hand, identification is the task of determining an unknown speaker's identity.
In a sense speaker verification is a 1:1 match where one speaker's voice is matched to one "voice print" or "voice model" whereas speaker identification is a 1: n match where the voice is compared against a number of n voice print samples.
Each speaker recognition system has two phases: i) verification phase and ii) identification. The systems involve enrolment (specimen recording) and verification. During enrolment, the speaker's voice is recorded and typically a number of features are extracted to form a voice print, template, or model. In the verification phase [which is similar to our case in question] a speech sample or "utterance" is compared against an acquired voice print or a previously created voice print. For identification systems, the utterance is compared against multiple voice prints in order to determine the best match(es) while verification systems compare an utterance against a single voice print. Because of the process involved, verification is faster than identification.
Speaker recognition systems fall into two categories: text-dependent and text-independent.
If the text must be the same for enrolment and verification this is called text-dependent recognition. In a text-dependent system, prompts can either be common across all speakers (e.g.: a common pass phrase) or unique. In addition, the use of shared-secrets (e.g.: passwords and PINs) or knowledge-based information can be employed in order to create a multi-factor authentication scenario.
Text-independent systems are most often used for speaker identification as they require very little if any cooperation by the speaker. In this case the text during enrolment and test is different. In fact, the enrolment may happen without the user's knowledge, as in the case for many forensic applications. As text-independent technologies do not compare what was said at enrolment and verification, verification applications tend to also employ speech recognition to determine what the user is saying at the point of authentication.
Multi-Speech, Model 3700, GoldWave 5.06 and ALIZE/SpkDet softwares are the latest brand names which use ‘state- of- the- art’ open source speaker recognition.
What type of CD was examined by both the labs?
To decide about the controversy in this case, we must first understand what types of CDs are normally submitted or distributed to media in cases of this nature. [The questioned CD said to have contained recordings of Shanti Bhushan purportedly telling Mulayam Singh that his lawyer son Prashant could manage a judge for Rs.4 Crores]. Such CDs are only ‘read only’ CD-Rs and not rewritable CD-RWs. Let us call such a CD as ‘CD-X’. If someone wants to splice different matter in these CD-Rs, one has to first copy the recordings from the CD-R to a CD-RW or alternatively to the hard disc of the computer and then only splice extraneous matter on to the original recordings. Then the recordings with splicing in the CD-RW can be burnt (copied) in a CD-R and distributed. Let such CD be named as ‘CD-Y’
In this case I do not want to discredit either the CFSL or the Truth Labs. Let us give credit to both the labs assuming that the reports submitted by both the labs are the outcome of their unbiased honest scientific examination. Then the controversy in their opinion is due to each of them examining different CDs; say CFSL examining “CD-X” while truth lab examining “CD-Y”. It then becomes just like the views expressed by the six blind after sensing different parts of the body of the elephant!
Both the labs have examined the CD submitted to them to assess the aspect of tampering. As I had mentioned earlier, what is important in this case is the speaker verification and identification. First to solve the dispute between the two labs, CD-X and CD-Y, rather to be on the safer side, true copies of the two CDs are to be exchanged between these two labs and let them get satisfied by examining the other CD. Or true copies of both the CDs can be examined by a third lab preferably in Europe (France or Germany). Then of course the voice spectrum from ‘CD-X’ can be analysed along with voice samples of suspected individuals to attribute the questioned voice in CD-X to a particular individual say in this case to Shanti Bhushan.
Otherwise I would consider that vested interests are abusing or misusing ‘bits and pieces’ of scientific information with ulterior motives to hoodwink the public and judiciary.
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