Recording question

[ric29]

I have got a digital voice recorder which has been used to record the speech of my friend in my old high school.
Because of some reasons, it was recorded by another person.
The whole speech has taken about two hours but the whole recording is about one and a half hour.
I have promised to find in which places this recorded audio file has been cut (edited) and I have tried to find something in the DCF but nothing obvious has been found.
Is any method which allows to find places where the audio file has been modificated (cut)?
Many thanx for any suggestion guys.

[Craig Maier]

Hi,

Digital Edits are hard to detect. Pros in the field use the Forensics version of the software coupled with the Hi-Res Spectrograph to identify suspicious sectors of the recording. You can download a trial version of that program from our website and it will be fully functional for 10 days. That may give you enough time to find the edits (if it is possible to do so at all).

Craig

[Dan McDonald]

You can listen (and look for in the spectrograph) changes in the background noise. A lot of times that's the most telling, but if it's just general crowd murmur, then it's going to be very hard to tell.

[ric29]

Thanx for answers guys

@ Craig
I use Forensics version. Can you pleas explain what you mean "Hi-Res Spectrograph"? Should I use any special settings?

@ Dan
Background noise in spectrograph seems to be a good idea. I'm just thinking about filtering only noises from the signal to analyse it-does it make sense?

[Craig Maier]

Hi,

You should look at the Spectrogram preferences and you will see a horizontal slider control called "Increase Resolution". Moving the control one way will increase the frequency resolution of the system at the expense of time resolution. Moving the control the other way will increase the time resolution of the system at the expense of frequency resolution. To futher increase the resolution of the spectrograph, you can increase the fft size up to as high as 131,072. However, be aware that large fft sizes will increase the refresh time required by your system.

Craig

[Dan McDonald]

I think Craig would know much more about this, but when I've had to do it for various things, I just look for anomalies in the sound and listen to hear if there is something going on that could explain it besides a cut. So I wouldn't filter anything out before looking - just look for changes in the general sound profile. But then again, this could be very hard to do if it is just a second or a few seconds and there is just a general noise in the background.

[Craig Maier]

I just know that it is a time consuming process, especially if the investigator does not know where in the recording that there are areas to be suspicious of. Once the area is known, the hi-res spectrogram can be helpful, especially in the hands of persons trained and experienced in its use.

Craig

[ric29]

Thanx a lot guys