Analysis of digital data

[ric29]

Although my question seems to be a bit off topics, I have decided to ask here.
To make a long story short: I've got from my friend very old computer tapes which stored old computer data.
The method of recording such digital data as an audio file on the magnetic tape is called "biphase mark code".
Such method (or similar)has been used in the magnetic stripe among others.
I have found interesting description here: http://blog.tehinterweb.com/?p=6
What I'm gonna do is decoding such data what is described in the above site btw.
Is any possibility to use DC Forensics8 for such purpose?
Or any other way?
Thanx in advance for any suggestion.

[Craig Maier]

Hi Ric,

The oldest format that I have some exposure to is PCM audio recorded onto Beta Video Tape in the NTSC format. I will ask Rick if he knows anything about "Biphase Mark Code".

Craig

[rickc]

Ric
I am familiar with that modulation technique for magnetic media, but we don't have anything in DC Forensics that could decode that.
Once you get the raw bits off the disk, the next trick will be to figure out if there is any other kind of encoding in the data. Most tape formats have some sort of blocking, error correction and compression on top of the raw bits.

Some new oscilloscopes have serial protocol decoders built in, which may work for this application. (assuming you had access to such a scope).

[ric29]

Great thanx for answers guys.
I have hoped there is any possibility to change (convert) the wave to text (values) what can allow to export them to any math/analitical software for any analysis.
Maybe it is worth to think about it in the future
Anyway thanx again.

[Craig Maier]

Hi,

I recall that there is an undocumented command to save a file as a data stream for use in spread-sheets or other similar programs. But, that does not specifically answer your query regarding bi-phase mark code. As I recall, the feature applies to any form of file that begins as .wav.

Craig

[Craig Maier]

Hi Again,

I found a post by Rick that has more information on this un-documented feature. Here is Rick's post:

---------------------------------------------------
I did put in a completely undocumented export feature to save the wave file as a csv or txt file.
To do this

Choose "File Save As"
Then choose All Files (*.*) as the format option
Then type in either .CSV or .TXT as the file name extension. (It will start out with a .*)



This will save the wave file data (no header info) as text. Either one coulumn or two for stereo. Both txt and CSV produce the same format. Which looks like this
0.0263398,-0.0325097
-0.0325097,0.0335345
0.0335345,0.0186791
0.0186791,0.0293102

The wave data is normalized to 1.0, so if you want the actual integer values you would need to multiply by the max bit weight (32767 for 16bit files)

[Dan McDonald]

Could these values be used to calculate the dynamic range of a recording?

[Craig Maier]

Yes they could, but I suspect it would be a lot easier to use the Diamond Cut Spectrograph. Click on the area of the softest passage and write down that value in dB. Then, Click on the area having the loudest passage and write down that value in dB. Then, take the difference between the two and that would be the dynamic range. Well, that is how I do it, anyway.

Craig

[ric29]

WOW Craig, amazing
Now it can be analyzed by Matlab or whatever.
Huge thanx

[ebrjvd]

There are tools and plugins available to display and calculate the DR, according to EBU standard R-128
http://www.dynamicrange.de
http://www.pleasurizemusic.com
http://www.toneboosters.com/tb-ebuloudness
http://tech.ebu.ch/webdav/site/tech/shared/r/r128.pdf

Jos

[Dan McDonald]

Thanks Jos. Will check these out.Dan

[Dan McDonald]

Jos -These don't seem to work. At least the plugins for Foobar, etc. are not working, and a number of posts indicate they don't calculate things correctly. Thanks anyway. I'll hunt for some other options.

[Craig Maier]

Folks,


If you can wait a bit, Rick and I are talking about building that into the next version (probably under the View Menu)

Craig

[Dan McDonald]

Sounds great, Craig. Sometimes I get interested in 'before restoration' and 'after restoration' comparisons.