Let me say that after reading the article, I am not buying the conclusion that it is not Zimmerman's voice. First let me provide some of my background experience, prior to focusing on financial software development, I spend the first 15 years of my career involved in telecom and voice software. I wrote code for voice mail systems, voice companding, dsp code, voice recognition, text to speech, T1/E1 digital links, codec, analog echo cancellation and VoIP packetization. The first problem I have with the conclusion is that the police 911 system probably uses voice compression when recording voice calls digitally which causes a loss of quality to minimize disk storage space requirements. In other words both 911 calls (Zimmerman's and the screaming) have quality issues that make them difficult to use for voice biometric identification. The second issue is that the call with the screaming probably is from a wireless home handset which uses some type of compression between the handset and the base causing quality issues and distortion. Similarly Zimmerman' cell call has the same problem but in the case of cell phones it is easier to correct for since a common known algorithm is used for cell phone communication. The third problem is that there is no sample of Trayvon Martin's voice used for comparison in an attempt to demonstrate a match. This is a critical issue. The fourth problem is that a rating of 46% with the Easy Voice Biometrics software is "inconclusive" not negative. Even if the voice definitely was Zimmerman's it is not surprising that a 46% score is achieved after all the compression that occurred at the 911 call center, wireless handset, and cell. Unless the items are corrected for then the score is going to be low. And to correct for them, the algorithm that is being used for the voice storage and handset communication must be known, simply trying to judge quality based on the signal-to-noise ratio is not sufficient. As a follow-up note, I will note that in the Davalloo case that was referenced, the criminal called from a pay phone in 2002 that did not use voice compression (only u-law companding). The 911 call center at the time used a Nortel or Lucent analog tape recorder with no digital voice compression. This made the identification of Davalloo much more straight forward. I question the statement that âthe audio from Zimmerman's call is much better quality than the 911 call in the Davalloo caseâ. My conclusion, his result that "you can say with reasonable scientific certainty that it's not Zimmerman" does not hold true. I think that Owen Forensic Services LLC is simply trying to get publicity to drum up more business. // Also I will note that Trayvon Martin's father said in an interview that the screaming is not his son's voice.
I do not understand the technology that you are talking about gwb, I only post the link to is what the company conclusion. Trayvon's mother always say that is her son's voice. His father is listening for the first time to the voice of his (dead) son. He has stress and deep sadness too. I do not know if he really say is not his son before, but he is heartbroken when he listen. But the Zimmerman family have no stress from death, only stress to prove George Zimmerman is innocent.
Going back to the days when modems and analog phones were all we had, I remember at the time learning that phones would only transmit within a narrow frequency where most normal voice frequencies would occur. Strictly technical question re the above: is this still true, or do cellphones now record a wider range of frequencies? Maybe that's what the people quoted in this article were referring to?
Analog phones carried about 3 kHz of voice bandwidth. Modern phones work with about 3.5 kHz but there are a variety of codecs used so there are a few types of distortion introduced by the conversion to digital. Phones typically cutoff the lower frequencies drastically. There should be enough information for voice analysis to distinguish between two people. The fact that Martin is unavailable to give voice samples could pose a problem.
What a yawner of a story. A thug got wasted.. I guess it's a lot better than "somebody worth something in life got wasted by a thug", or "man bites dog".. Did any cities burn yet? Let me know how that works out, ok? I don't live near any city but if I see a blaze way off on the horizon I promise, I'll do a moment of silence thingy for the thug... no, really, I'll take my hat off and everything...
Voice on telecommunications circuits still is limited to the 300 Hz to 3400 Hz frequency range. This has not changed with the advent of cell phones. The range of human voice is 80 Hz to 14 kHz. One reason for this is that cell phone calls still get routed over the standard telecommunications network after leaving the tower. When a cell phone call is made, the voice compression between the cell phone and the tower is usually one of the more modern voice schemes, but still limited to 300 Hz to 3400 Hz. For example if the cell network is GSM then CELP coding will be used for the voice. At the cell tower the call will be routed to a standard MSC Telco switch which will convert the CELP to standard 8 bit u-Law PCM companding that is used in the US. This 8 bit sampling allows 64 Kbits to be used for each voice call which can be multiplexed up in T1 circuits (23 channels of voice plus one signalling for ISDN-PRI or 24 channels of voice with SS7 signalling being used out of channel). So in answer to your question, cell phones do not do a wider range of frequencies today and improve voice quality in any manner. There can be an argument made that echo cancellation algorithms have improved, but not to the point where the quality of a cell phone call will exceed that of a landline phone.
Actually, this bit about Neighborhood Watch programs is interesting... "Some German states, such as Bavaria, have instituted systems of citizen patrols (Sicherheitswacht) where unarmed teams of two volunteers patrol assigned areas to improve subjective security. These teams carry a radio to call for help if necessary and a white armband with black letters identifying them as a neighborhood watch patrol." Looking again at the video of Zimmerman at the police station after the shooting, is he wearing any identifying N.W. gear? Would some identifier be on his car? Because if a guy packing heat comes up to you, and he doesn't have any law enforcement identifier, how do you know he's not going to be mugging you?