[sdiy] equalizer

[cheater cheater]

I'll keep the book in mind,
thanks!!

How did you come up with "Q between 0.707 and 1"?

Cheers,
D 8)

On 10/9/05, harrybissell <harrybissell at prodigy.net> wrote:
> cheater cheater wrote:
>
> > Well, what I want is a narrow cutoff (like 24 dB/oct? no idea - hints?)
> > Usual equalizers have 6 dB/oct - right? Or is it 3?
>
> Most are 12dB, some are 18dB.. I don't know of any common 24dB designs.
>
> > So at 24 dB/oct:
> > 1. The BP would be real narrow and resonant and crappy and shtuff
>
> 24dB could still have low, or high resonance.  Q of .707 to 1 would not have
> a pronounced peak. BTW the BPF of the state variable is only 1/2 the cutoff
> rate of the HPF and LPF.  The 'state variable' design in most commonly a
> 12dB slope. You 'can' co a 24dB but it gets complex
>
> >
> > 2. The HP and LP would already give me the whole spectrum. So the BP
> > would only add stuff - am I right? Or would HP+LP=everything-BP? :)
> >
> > And in other news:
> > can anyone recommend a filter that:
> > 1. doesn't have a very resonant sound
>
> any one with a Q of .707 to 1...
>
> There are a number of standard filter designs. For memory I will fvck this up
> and my listmates will jump my bones. They are Butterworth, Bessel, Chebychev.
> One has better flat gain in the passband, one a better cutoff but small peak at the
> corner, one has ripple in the passband but even sharper cutoff. They have different
> shape of phase shift as well.  Decisions decisions. Most folk use the Butterworth...
>
> > 2. has a pretty narrow cut-off (24? 12? 18 dB/oct? which ones would you choose?)
>
> 12dB
>
> > 3. has a pretty uncomplicated circuit (I'm going to have to have a lot
> > of these in an equalizer it seems - and even more in a whole mixer -
> > woe is me!)
>
> There are a lot of circuits. I'd start with one I like, then copy that first to get
> experienced..
>
> 4. (a plus but not needed) sweeps don't have the usual cheezy resonant whistle sound
>
> >
> > This goes for LP and HP. I'm counting on you synth freaks here!
>
> If you need to sweep the filters, for sure the higher cutoffs will need more
> components. Usually a 12dB needs two tuning elements (dual pot, ota etc)...
> 24dB needs 4 etc.
>
> >
> >
> > Regarding 3 - am I right to think that SMD components would make the
> > [6x2x5=60 (!!!!) (4 bands)x(stereo)x(5 channels)] SIXTY filters easier
> > to tune up? Don't they usually fluctuate less? In any case I guess
> > it's a must considering space and such...
> > I'm *so* buying metal film resistors... and 2% caps.... *cringes*
>
> and good caps are hard to find... especially in SMT
>
> > Also: anyone got the Electrix EQKiller schematic?
> > Or the Vestax DCR-1200 Pro?
> > I'm very curious what kind of filters they're using, and what order they are.
>
> I'd recommend that you get a copy of the old National Semiconductor "Audio"
> or "Audio/Radio Handbook"  (out of print but I think someone sells reprints). The
> ICs shown are largely obsolete but the concepts are still quite valid, and it is
> written
> for the common man (well, common man skilled in the art :^) to understand. It shows a
> graphic EQ and a 'room equalizing instrument' that are of interest.
>
> H^) harry
>
> >
> >
> > Cheers!
> > D.
> > 8)
> >
> > On 10/8/05, harrybissell <harrybissell at prodigy.net> wrote:
> > > Steven Cook wrote:
> > >
> > > > A state-variable filter has three simultaneous outputs: lowpass, bandpass
> > > > and highpass. I suspect that mixing all three outputs together would
> > > > reconstruct the input signal with reasonable accuracy.
> > > >
> > >
> > > True... but the corner frequencies cannot be (individually) controlled... and are
> > >
> > > really unlikely to be useful in an EQ application.
> > >
> > > H^) harry
> > >
> > >
>
>