There are four different type of digital filters:
- Low Pass Filter (FATL/SATL, RFTL/RSTL, KGLP);
- High Pass Filter (KGHP);
- Band Pass Filter (RBCI, KGBP);
- Band Reject (stop) Filter (KGBS).

What are KGLP, KGHP, KGBP and KGPS?
What are the differences between FATL, SATL, KGLP etc?
All the filters are utilized Park Mc Allen algorithm of synthesis of digital filters by two methods:
- some filters are based on article of Jake Janovetz, 1995 (http://www.dsptutor.freeuk.com/remez...rDesign.html);
- some of them are based on digital signal processing library MtxVec 1.51, having algorithm, described in: Discrete-time signal processing. Openheim and Schafer, Prentice-Hall, 1989 and Theory and application of digital signal processing, Lawrence R. Rabiner and Bernand Gold. Prentice-Hall, 1975.

In other words, the Low Pass Filter (FATL/SATL, RFTL/RSTL, KGLP) is gating the fluctuation with the frequency less than specified.
High Pass Filter (KGHP) is gating the fluctuation with the frequency above (higher than) specified.
Band Pass Filter (RBCI, KGBP) is gating the fluctuation with specified band.
Band Reject Filter (KGPS) is gating the fluctuation except specified band.

The pictures attached show parameters of Low Pass Filters. The axis X of the picture 1 is a period, and on the picture 2 is a frequency.

Pass band cutoff frequency of LPF, P1 (bars):
- the cutoff expressed in bars. All swings of the price of the period more than P1 will be suppressed. In classical MA it corresponds to the moving average period.

Stop band frequency, D1 (bars):
- transient period. The recommended value for FATL is 2 days. For slow filters such SATL the difference between D1 and P1 need to be more significant.

Ripples in the pass band, R (Db):
- That value needs to be set up as low as possible in order to decrease distortions.

Stop Band attenuation, A1 (-dB):
- That value defines attenuation in stop band region. The recommended value is - 40dB that corresponds to 100 times attenuation.

Delay, Bar:
- That value defines a delay of the digital filter expressed in bars, for RFTL and RSTL to be more smooth and predictable.

For the FATL or KGLP the recommended parameters are P1=10; D1=8; R=0.0864, A1=-40; and Delay=0;
or 13; 10; 0.06; -40; 0;
or 25; 13; 0.001; -60; 0.

For the SATL/KGLP:
79; 35; 0.039; -40; 0; or
49; 25; 0.024; -40; 0; or
50; 26; 0.001; -60; 0.

For RFTL and RSTL the recommended parameters are the same with KGLP but delay should be above zero integarl number.

But we may use our own settings according to the pairs, timeframe etc.

Attached Images

	lowpass1.bmp (61.7 KB, 1357 views)
	lowpass2.bmp (61.4 KB, 1166 views)

Calculation of band pass (indicator KGBP, RBCI) and band stop filters (indicator KGBS).
Three extra input values are needed for such filters (see pictures).
Additional parameters are used:
- Pass Band Cutoff frequency, P2.
- Stop Band frequency, D2
- Attenuation in Stop Band region, A2.

Other parameters are the same, as at the filters described above.

Attached Images

	Band_pass_filter.bmp (60.8 KB, 1193 views)
	Band_stop_filter.bmp (61.4 KB, 1102 views)

All the calculation you may do using the small software (see download area)
by one click to have the indivcator for MT3 or MT4.

Besides, you may create any combination of filters in one indicator.

And what is more, you can estimate all the parameters using the chart with your desirable pair and timeframe.

And more: you may compare the characteristics of several filters and you may see it on the charts.

Besides, you may use dll files to create any filter in MT4 even without any software.

We may prefer to use digital filters which already have in our computer or digital filters from this forum (see download area)? Yes, we may do it. At least we know everything about the parameters of the indicators and we are able to use it in the EA developing.

It was a story about the army and navy, Royal Military Academy and russian people from Siberia.

Next time we will go into practics: we will try to create the figital filter indicators for MT4 and MT3, will compare the indicators with each other and will try to use those indicators.

Great
Thanks

As you know in download area we posted software to generate any digital filter for metatrader. But if you prefer to use metatrader only to do everything we have the special indicator for that case which you can use instead of this software.

To use this indicator you must copy DF.dll file to \experts\libraries\ folder and make sure availability of Bdsp.dll, lapack.dll, mkl_support.dll in C:\Windows\System32\ folder or or in \experts\libraries\. Check "Allow DLL import" and "Confirm DLL function's call" in Options->Expert Advisors.

Check download area

I was inhibited by the selecting the parameters for digital filters, it means P1 etc. We are able to create the indicator but we need to select the patameters.
So, need a break.

Does anybody know?