суббота, 5 сентября 2009 г.

SA Update: version 6.0.6.4.

SA Update: Version 6.0.6.4
Reverse synthesis of FSK/MFSK signals.


New in version 6.0.6.4:

  • the minor problems are solved
  • some algorithms are optimised
  • ability of reverse synthesis FSK/MFSK of signals is added

What is the reverse synthesis for? There is the certain problem with the signals, which have poor enought quality. If, in SA, it is possible to define parametres, and there is the possibility to save the signal in the better quality compare to initial one, then it is desirable to do it. We will consider a standard example.

The record Piccolo-12 from the site http://www.signals.taunus.de/FFT/PICC-MK12-TFC.jpg, by the way, is the only one record, which is managed to be found in Internet by me. It is well-visible, that the level of interferences is very high. Standardly used, in such cases, amplitude limiters do not make the situation better.

Nevertheless, SA allows to define paremeters of this signal reliebly enough, and moreover, SA allows to save the resulting signal in the much better quality.

Reverse synthesis removes both out-of-band noises and interferenсes and in-band ones, which are hardly can be removed by other tools. The difference is perceptible both by ear and by sonograms:


Reverse synthesis in SA, restores the signal in the same frequency positions, and with the same frequency spacing and speed of manipulation, as an initial signal.

There are more examples:

BulDiplo - is the high-speed enough signal.

On the record of Chinese modem MFSK-64 - almost complete suppression of noise is well visible.

Ofcourse, reverse Synthesis, as any other tool, has it's own field of application.

No need to use it too much and all the time, no need to expect that this tool will solve all the problems with the noisy records.

The positive accuracy and thoughtfulness is needed, some experience and skills are also required.

Attention please: Never represent similarly edited records for analysis.

Everywhere and always I insist that the analyst should have for the analysis completely initial, not touched (and not edited) material. Only the analysit solves what to do with this material and how to do
it.

Reverse synthesis is the tool of analysis, but not the tool of decoration of the records for the further analysis.

Good Luck!

The small series of the articles about Scramblers by MSM Group. Direct Inversion.

Direct inversion.
Final Part III.
Direct inversion of speech spectrum.

Author: SergUA6 6.0
Band Width 2700 - 3400 Hz, it can vary, depends of tasks.
Low Range 100 - 300 Hz, it also can vary.
RX mode All types of modulation.

Sonograms

pic.1 Spectrum of inverted speech


pic.2 Spectrum of normal speech


1. The example of inverted speech, point(frequency) of inversion is 3600 Hz.

2. Exactly restored inverted speech.

Direct (simple) inversion - is the direct(simple) inversion of spectrum. It is one of the most widespread sorts of speech's masking. It is easily recognised by ear (in the case of absence of the strong interferences) and by the form the spectrum: it is well-visible on the spectrum, that the main energy is concentrated in the upper band of the frequencys, what is unusual for speech. Those who saw a normal spectrum of speech and inverted atleast once , will unmistakably define inversion further, even if it is got mixed up with other features. For today this sort of masking Makes impression unless on absolutely trustful people. Direct inversion is easily defined, easily removed, and in general it is more suitable for creation of insignificant minor problems , than for masking.

Nevertheless, the direct inversion is still widely spread today, by virtue:

  • of it's simplicity
  • of the absense of synchronization (the weak place of all synchronized scramblers)
  • of the posibility to work in conditions of the strong interferrences
And anyway the function of the fast hiding of information is realized, althought the direct inversion isn't a barrier even in real-time.

The inverted spectrum is very easily formed by following steps:
  • the frequency of inversion usually around 3000-4000 is selected
  • after multiplication of an initial signal (speech) with this frequency is occuring
  • then the lower lateral is selected from resulted DSB signal. This lateral is the inverted spectrum of the initial signal

The modern tools allows to do it very qualitatively. The same manipulations with the signal are used for restoring.