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I am trying to find out if it is indeed possible to do real sound analysis on a digital source sound file, to determine for example, if the voice of someone in an audio file is the real one or only fake. Let us assume the audio file is an mp3 file. Is it possible to determine without a doubt that the voice heard there is from the original source (The original person) by only checking the Digitized sound file (MP3 Format).

How does doing this with an analog source and a digital source differ for the same sound analysis purpose?

What are the differences between analyzing the voice over an Analog source and a Digital source and what are the disadvantages (If any) when trying to determine if the voice is real (For the case mentioned above).

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Thanks for the accept, but you should really wait at least 24 hours before accepting an answer. I'm obviously biased in favor of my own answer, but there are plenty of people here who may be able to offer more nuanced answers to your question. –  ObscureRobot May 24 '13 at 0:05
    
@ObscureRobot thanks, will wait until another answer appears. If in indeed is good then I will move the accepted answer. –  Luis Alvarado May 24 '13 at 0:10
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sounds good. Accepts tend to discourage others from asking, so you might want to wait in the future. –  ObscureRobot May 24 '13 at 0:25
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I'm having difficulty understanduing how you would verify the authenticity of any audio source in any format. What do you mean by this? Is there a link to understanding this better? –  Andy aka May 26 '13 at 18:29
    
I agree that a correct answer very likely hinges on a detailed technical understanding of what verification means in this context (and which context this is). –  ObscureRobot May 26 '13 at 22:00

2 Answers 2

An MP3 file is a very poor source for any kind of analysis. This is because MP3 files involve lossy compression, and the degree of compression can vary depending on how the file was encoded. The lossy compression process removes content that the human ear-brain system doesn't notice, but some of that information may be relevant for the type of forensics you are proposing.

However, if you want to do digital forensic analysis on a signal, you will have to work with a digital file of some kind. Ideally, you will work with an uncompressed audio file such as a WAV or AIFF. There are a wide variety of digital signal processes and algorithms out there, so digital is probably the domain you want to work in.

If you want to deal with pure analog, then you have to remain in the analog domain. That probably will require construction purpose-specific equipment.

Is it possible to determine without a doubt that the voice heard there is from the original source

This sounds like a legal definition or other domain-specific definition that you are describing. What does "without a doubt" mean? What does "is from the original source" mean?

Some of this analysis will necessarily be out-of-band. What I mean by that is that a digital file can be duplicated and copied. Certain kinds of filtering can be applied after the fact that could be reasonably expected to have been applied at recording time - such as low-pass or high pass filtering or dynamic range compression. It may be very hard or impossible to prove when this kind of transformation was applied to a signal regardless of whether you are dealing with analog or digital material.

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The main challenge with digital audio is that it is difficult to tell if it has been edited or spliced together since there are no generations of loss. A lossy format such as MP3 would further complicate this as it would make any minor issues with cutting things together more difficult to distinguish. It should be easy enough to identify the speaker, but ensuring that the recording is unaltered could be very difficult.

As for analog vs digital, the fact that digital audio technology exists ends up being a problem for analog records as well. Since a digital recording could be transferred to an analog tape, there is no way to verify that an analog source was not digitally altered, so really the existence of digital technology alone makes it a problem, though a lower quality digital audio file or a low quality analog file could be problematic.

The ideal would be a high quality digital file that is free from distortions. Either an analog source or a low quality digital source would both have distortions that make things more difficult.

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and this is why you shouldn't accept the first (my) answer you get! –  ObscureRobot May 24 '13 at 3:57
    
@ObscureRobot - though in fairness, I still would have responded anyway. :) –  AJ Henderson May 24 '13 at 15:25

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