Knowing absolutely nothing about analog audio processing or electronics, I can nonetheless imagine that the reason why classic EQ's like the 1066 and 1073 had fixed frequency bands was something to do with the values of off the shelf electrical components (although I'm sure someone will put me straight). However, I was wondering if there was a good reason why digital emulations of these EQ's have the same restrictions, other than authenticity and the fact that they're modeled from the original designs? For instance I love the sound of Waves V-EQ3 when making boosts, but oftentimes find myself wishing that I could sweep somewhere between 3.8kHz and 4.8kHz to find the spot I want, instead of having to choose between those two frequencies. I guess what I'm curious about is, is part of the character of these EQ's a product of the fact that they have fixed bands, or is there no reason why we can't have an EQ with the same sonic character but with sweepable bands? 

they are copying the original circuits, as close as possible, for good or bad

In hardware, fully-parametric filters are expensive - and the cost is multiplied by however many channels your console has. That's one reason they've historically been fixed.
 
The other is that it's quicker to dial in an EQ when you have the same filters on every channel. You give up some flexibility but gain ease of use. This is the reason software continues to emulate that design, even though the cost factor no longer applies.
 
What I don't buy into is the concept of "magic" crossover frequencies, where you're told the EQ works well because of the particular fixed frequencies they've chosen. That's BS. The real benefit is being able to quickly tweak the EQ because you've become habituated to its characteristics.
 

twice this century, but I'm going to have to respectfully disagree with Mr. Bit...
 
There are some "magic" filters out there - might be the cut-off frequency, might be the topology, might be the parts used, I have not yet figured that part out yet, but there are filters that I use because they are just musical. Oddly enough, most are fixed frequency filters - for all the other reasons you listed, but cost is probably the predominant reason.
 
Examples - the classic Pulteq filters seem really well placed, now do we like them because they are in the right spot or are they in the right spot because we've become accustomed to them?
 
One of my favorites, strange though it may be, was a cooperative effort between Haffler and Rane - this funky little 1 RU guitar preamplifier that had the most musically useful (for a guitar) tone controls. They didn't even call them filters<G>!
 
Another favorite was the tone controls on this old Heathkit preamplifier. The filters are all passive, but they just work musically.
 
Symetrix used to make a couple filter sets that were really useful, and the Urei "Little Dipper" is another one from that era that I really liked.

For modern gear I don't think you can beat the MAAG EQ, that thing is just magic!

Anyway, choice of cutoff frequency is very important, and highly subjective<G>!
 
Bill

I also wondered if there were some mathematical reason why certain frequencies were easier to manipulate. These are the sort of things that flit about one's head when one knows nothing about a subject 
 
Anyway I can see the advantage of only having limited frequencies to work with. I must admit I do get carried away sometimes with trying to be "exact," i.e. boosting a certain frequency in one instrument and cutting exactly the same frequency in another. Other times, for instance when giving a little clarity boost on a guitar, one of the frequencies on the V-EQ3 seems to work great no matter what the source. 

Bill, I thought you were a modern, enlightened and educated guy!
 
Magic? Really? Musical filters? Dude!
 
If you're gonna refute me you'll have to throw in at least a little science. Just to shut me up if nothing else. Next you'll be singing the praises of A-432 and homeopathy! 

sharke
I guess what I'm curious about is, is part of the character of these EQ's a product of the fact that they have fixed bands, or is there no reason why we can't have an EQ with the same sonic character but with sweepable bands? 

Their are certain DSP issues involved with making sweepable bands. Not necessarily dealbreakers, but issues.

That would appear to explain the crackles and pops I hear when sweeping bands on the QuadCurve.

bitflipper

bitflipperBill, I thought you were a modern, enlightened and educated guy!

Not me... I'm a dinosaur through and through - still have a couple of tape decks even<G>!
 

bitflipperMagic? Really? Musical filters? Dude!

So maybe that's a little over the top, hyperbole even?
 
But yes, I do believe that some filters in some devices are more pleasing to some folks. And I do not think any chickens sacrificed in order to pull it off!
 

bitflipperIf you're gonna refute me you'll have to throw in at least a little science.

This is where science and art start to blur together I'm afraid. This has more to do with psychology than electronics or acoustics, but I believe that the effect is very real.
 
Think about the number of devices with identical, or nearly identical measurements (S/N, THD, IMD, etc), yet sound markedly different. There are also cases where two devices sound strikingly similar but may have diverge when measured.
 
As a specific case - I built a handful of headphone amplifiers, most were class A circuits, but a couple were Class A/B, and they used a variety of bias methods, including constant current sources. I used bipolar and field-effect transistors in almost all the different approaches.
 
Granted my test gear is getting old (Sound Technology ST-1710A, ST-1510A, and ST-3000, and Amber 4400A), but I was able to measure meaningful levels of noise and distortion in most of the circuits.
 
What did my ears tell me you ask? I'm glad you did...
 
There was very little correlation between lower numbers and what I liked. There was the hint of a correlation, or at least repeatability, in that I seemed to prefer Class A over Class A/B, but not enough to be compelling. (Maybe in a high gain preamplifier stage, but not in a power amplifier stage.)
 
My point being that there are some things, even in the little old world of audio, that we can't pin down - scientifically at least - just yet.
 

bitflipperJust to shut me up if nothing else.

 
That has never been my goal!
 

bitflipperNext you'll be singing the praises of A-432 and homeopathy! 

 
Don't hold your breath for that<G>!!

Musical... because DimeBag used a Furman PQ3, which was totally sweepable too.  :-D
 
Then those old Moog parametrics...  I guess if you're a synth player and need something for your 2600 ??