[RTTY] Dual Peak Filter question

[RLVZ at aol.com]

I appreciate the discussions on this reflector as I still  have a lot to 
learn about RTTY.  
 
Based upon the information below that basically contends that  "software 
based dual peak filters outperform the a rigs dual peak DSP  filter" can I 
assume then that I'd do better during RTTY contests by  turning my K-3's dual 
peak filter off" and turning on the MMTTY dual peak  filter?  (I have never 
tried MMTTY's dual peak filter)  In case it matters, I have 250hz and 400 hz 
roofing  filters in the K-3. 
 
Thanks & 73,
 
Dick- K9OM
 
 
As such,  optimal filtering for digital modes is better achieved in the 
software modem  than by using approximations in the DSP stages of the rig.  And 
software  UI can be simplified to anything that you wish.

With the processors in  today's computers, there are not that may things 
DSP processors can do in real  time that the computers cannot also in real 
time, where latency is not a  problem (the exception is the decimation process 
of the direct SDR that starts  at 70 MHz).  

A dual peak filter (usually done in the DSP stages  of a rig) is just an 
approximation of two narrow bandpass filters around each  of the two RTTY 
tones.  This is what produces the "depression" between  the two tones.  It 
approximates what a pair of matched filters does in  software that supports 
matched filtering.  In fact, one thing to note is  that if the software already 
implements matched filtering, engaging a dual  peak filter will make copy 
worse, not better.  If copy gets better, it  means that the software filter is 
not optimal.  

A simple dual  peak filter cannot track the baud rate of the RTTY signal 
(at least I have not  seen one that does).  I think RITTY's matched filter is 
also fixed at  45.45 baud, but there are other software that implements 
matched filtering  which tracks the baud rate when you change it.  In the case 
of RTTY, a  matched filter has an impulse response that corresponds to the 
rectangular  pulse of the demodulated RTTY signal, i.e., a pair of sin(x)/x 
shapes in the  frequency domain.

73
Chen,  W7AY