The RCOSFLT function has changed significantly in Release 12. The changes are improvement on the basic operation of RCOSFLT and the removal of features that were misleading to our customers:
1) Removal of the truncation of the early tail of the raised cosine filter.
The R11 function was incorrectly using the results of the RCOSFIR function to filter the signal. The raised cosine filter is a FIR filter with linear phase. Therefore, the filter must have a symmetric impulse response. Truncating the early part of the impulse response violates this rule.
2) Removal of the decimation stage of the RCOSFLT operation.
In Release 11, the RCOSFLT function, zeroed out all but every Nth sample when the Fs, sample rate was set to N. This is an approximation to the more correct operation, which is to precede the raised cosine filter with a 'sinc' filter. The decimation was removed because it appears that this was added to make the RCOSFLT work well with our DMOD() and MODMAP() functions.
