Newsgroups: comp.speech
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From: jimn8@netcom.com (Jim Nitchals)
Subject: Re: Tomorrows World Speech Recogniser
Message-ID: <jimn8CoIv7D.JJ@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
References: <2otn0a$dcm@bambam.cs.city.ac.uk> <1994Apr19.111807.8191@leeds.ac.uk>
Date: Tue, 19 Apr 1994 19:52:25 GMT
Lines: 40

een6njb@sun.leeds.ac.uk (N J Bailey) writes:

>I didn't see the programme, but I bet it detected wow & flutter to decide
>whether the source was tape or voice.  So if you want to break in, use
>a DAT Walkman!

Detecting a regular analog tape is possible, given enough source
material.  Just look for dropouts.

That's too easy, though.  Let's look at ways to defeat DAT recorders.

If the system remembers every instance of the subject making the sound,
or passphrase, it might be able to reasonably detect a recording based
on word durations and pitch information.

Spectral characteristics of real voice are likely different too.
You'd need good, flat frequency response, including speakers with
good bass, for starters.

You'd then need to alter word durations and pitching.  This isn't as
easy as it sounds, although if you're a spy trying to break into the
enemy's HQ it'd be worth the effort to do properly.

You could also trick the target into speaking the passphrase, or
parts of it, in a situation away from the security system.  The
users would undoubtedly be warned to look out for attempts of this
sort.

>I'd be interested to hear from anybody on this subject who knows what they
>are talking about!

Apologies for offering mere conjecture, although I do sound and speech
processing software as part of my job.

- Jim Nitchals

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