if you sample a signal at 6khz this implies that your input signal is banlimited to 3khz. there fore there will be no problem if there is an extra band at 3khz-6khz.this duplication is due to the nyquist rate sampling.( reflection about fs/2). if your input signal bandwidth is more then sample the signal accordingly (twice). nitthilan --- Priyank Saxena <> wrote: > This problem is inherent in any real signal. Only a > complex signal can have a > single sided spectra. > One more way of avoiding this band without > increasing the sampling frequency is > to use the hilbert pair of your filter and construct > a complex signal. This > will then have only the desired frequencies between > 500-1800 Hz. > > say x is the input, h1 your filter and h2 the > hilbert pair of h1 then: > y1 = filter(h1,1,x) > y2 = filter(h2,1,x) > y = y1 + j*y2; > > If u have used 'remez' for designing the filter 'h1' > then the same can be used > for designing 'h2'. All u have to do is to add one > extra argument at the end > ('hilbert'): > h1 = remez(..,..,..,.........,); > h2 = remez(..,..,..,.........,'hilbert'); > > -priyank > --- Goran Stepanovic <> wrote: > > There is always two identical, like in mirror, > spectras between 0 and 2*pi > > (corresponding to sampling freq.). Check out > "sampling theorem". If you > > don't want that band your sampling rate should be > at least 12kHz. > > Goran > > > > > Hi all, > > > > > > I am beginner in digital filter design. > Currently, I am designing a > > > bandpass filter cut-off at 500hz and 1.8khz, > with sampling frequency > > > 6k Hz. I use butterworth filter with order 6 > according to the > > > specification. However, when I try to plot the > signal, there is > > > passband gain between 3k and 6k Hz in addition > to the band before 3k > > > Hz. The passband gain between 3k and 6k Hz is > unwanted. Is there some > > > way to remove the gain of this part or should I > redesign the filter? > > > > > > Thank you for your help. > > > > > > Best Regards > > > Henry > > > > > > > > > > > > > > > _____________________________________ > > > Note: If you do a simple "reply" with your email > client, only the author > > of this message will receive your answer. You > need to do a "reply all" if > > you want your answer to be distributed to the > entire group. > > > > > > _____________________________________ > > > About this discussion group: > > > > > > To Join: > > > > > > To Post: > > > > > > To Leave: > > > > > > Archives: > http://www.yahoogroups.com/group/matlab > > > > > > More DSP-Related Groups: > http://www.dsprelated.com/groups.php3 > > > > > > ">http://docs.yahoo.com/info/terms/ > > > > > > > > > > > > __________________________________________________ __________________________________________________ |