Raised Cosine filters are a special type of filter used in many digital data applications to eliminate Intersymbol Interference (ISI).

ScopeFIR's Raised Cosine Editor is shown below:

To design a Raised Cosine filter:

• Specify the sampling frequency by hitting the Sampling Frequency button in the upper left. You will be prompted to enter the numerical frequency and the units of frequency/time.
• Enter the Rolloff factor (also sometimes called "Beta" or "Alpha".) This parameter ranges from 0.0 to 1.0, and is given as a system specification in digital data systems which use Raised Cosine filters.
• Enter the Filter Length. You may enter length in terms of either Symbols or Number of Taps. By Symbols, we mean that the length is specified in terms of some number of symbol periods. When you specify length in Symbols, ScopeFIR automatically calculates the Number of Taps by using the Sampling Frequency, the symbol rate, and the number of symbols. Alternatively, you can just enter the Number of Taps directly.
• You can also (optionally) Zero Pad your filter to achieve some specified total number of taps. This option is typically used when you want to design your filter for an odd Number of Taps, yet you need its actual length to be a multiple of the number of Samples Per Symbol. For example, assuming you have 8 samples per symbol, you might wish to design a filter to have 47 taps (so it's center coefficient value is a peak), and then Zero Pad it to 48 taps, so the total number of taps divides evenly by 8. In this example, you will then be able to decimate or interpolate by a factor of 6.
• Enter the Symbol Rate in terms of either Samples Per Symbol or just Symbol Rate. You must enter Symbol Rate in the same units as Sampling Frequency.
• You may also specify that the filter be a Root Raised Cosine filter. "Root Raised Cosine" filters are used for applications where the overall Raised Cosine frequency response is equally divided between the transmitter and the receiver; both the transmitter and the receiver implement a Root Raised Cosine filter.
• Finally, when all specifications have been entered, hit the Design button to actually design the filter coefficients.

Once a filter has been designed, you can check its Frequency Response. If the Automatic option is enabled, ScopeFIR will show you the frequency response at zero, at half the Sampling Frequency, and at the two Raised Cosine corner frequencies, which are (1 - Beta) / (2T), and (1 + Beta) / (2T), where "T" is the sampling period. (See Using the Frequency Response List for more information on the Frequency Response list.)