On 22/07/15 15:40, Tom Rondeau wrote: > On Wed, Jul 22, 2015 at 4:57 AM, Daniele Nicolodi <[email protected] > <mailto:[email protected]>> wrote: > > On 21/07/15 21:39, Tom Rondeau wrote: > > Here's my presentation from last GRCon: > > > > http://gnuradio.squarespace.com/grcon14-presentations#tut-rondeau > > Hello Tom, > > browsing through your presentation I see that on page 58 and 59 you > recommend to use firdes filter design tool and not optfir to build re > reconstruction filter. However, I don't quite understand why the filter > generated by one tool is better than the other is this case. > > Can you please comment on it? > > Thanks! Cheers, > Daniele > > > The shape of this filter matters greatly. The inband, transition, and > stop band behavior all determine if the filter can be used for the > reconstruction purposes. The image on slide 59 shows the specific > transition between the pass band and stop bands. To match that with the > PM (i.e., Remez) algorithm, you can't get the same stop band performance > for that given transition. Plus the equal response in the stop band is > bad when channelizing because all channels will alias at equal powers, > whereas the roll off in frequency with the windowed (firdes) filter > continues to decrease with f. Remez also produces a pass band ripple, > which will also affect things. The ripple with the firdes is not > equiripple like Remez promises, but it's much, much smaller.
Thanks Tom, very clear explanation. Cheers, Daniele _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
