Best way to remove a known frequency
in [DSP]
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From: Dirk Bell on 24 Mar 2010 17:14 On Mar 24, 4:22 pm, "gretzteam" <gretzteam(a)n_o_s_p_a_m.yahoo.com> wrote: > Hi, > Ok here are some clarifications: > > >> Has the OP stated to what extent it is important to preserve the > >> signal around 2 KHz or below it? > >> Makes a difference in the solution. > > This is for a medical application. Basic signal flow is: > > DDS -> DAC -> Human body -> ADC -> Decimation -> Detect AND get rid of > 2kHz. > > >> The 2kHz is exact fraction of 128kHz by exact binary ratio of 64. So > >> generating and using it is not a very good idea anyway. > > It's actually close to 2kHz, not dead-on 2k. > > The main problem is that the notch filter, or any other solution, need to > affect square pulses as little as possible. > > Hope this clarifies things a bit. > > Thanks! Square pulses at what frequency? Dirk
From: Dirk Bell on 24 Mar 2010 18:02 On Mar 24, 4:22 pm, "gretzteam" <gretzteam(a)n_o_s_p_a_m.yahoo.com> wrote: > Hi, > Ok here are some clarifications: > > >> Has the OP stated to what extent it is important to preserve the > >> signal around 2 KHz or below it? > >> Makes a difference in the solution. > > This is for a medical application. Basic signal flow is: > > DDS -> DAC -> Human body -> ADC -> Decimation -> Detect AND get rid of > 2kHz. > > >> The 2kHz is exact fraction of 128kHz by exact binary ratio of 64. So > >> generating and using it is not a very good idea anyway. > > It's actually close to 2kHz, not dead-on 2k. > > The main problem is that the notch filter, or any other solution, need to > affect square pulses as little as possible. > > Hope this clarifies things a bit. > > Thanks! Square pulses at what frequency? Dirk
From: gretzteam on 24 Mar 2010 18:11 >Square pulses at what frequency? Well hopefully your heat is not about to explode, so say about 1Hz! Should be about 100us wide. Every notch I'm trying is pretty much killing this, unless I make it really really narrow. I'm still struggling getting the idea to cascade a few notches to work. I think I missed the part about filter Q back in college! Thanks!
From: Dirk Bell on 25 Mar 2010 09:47
On Mar 24, 6:11 pm, "gretzteam" <gretzteam(a)n_o_s_p_a_m.yahoo.com> wrote: > >Square pulses at what frequency? > > Well hopefully your heat is not about to explode, so say about 1Hz! Should > be about 100us wide. > > Every notch I'm trying is pretty much killing this, unless I make it really > really narrow. I'm still struggling getting the idea to cascade a few > notches to work. I think I missed the part about filter Q back in college! > > Thanks! So you have basically a very impulsive rectangular waveform at a 1 Hz repetition rate with harmonics spaced at 1 Hz intervals. That is almost 2000 harmonics before the 2000 Hz tone. Have you done a matlab simulation to see how many hamonics you need for your purposes and what notch width at 2000 Hz works okay (ie how many harmonics you can acceptably remove around 2000 Hz)? Is there anything besides more harmonics above the 2000 Hz tone? Dirk |