[sdiy] equalizer

[Johannes Öberg]

In reply to cheater cheater:

>no... What I think I'll build would:

> 1. break up audio into several bands using LP/HP filters
> 2. set the gain of each of the bands separately (so, as you see, it
> doesn't necessarily "kill" those bands, it just separates them much
> more sharply)


Yep, but this is _not_ what I'm _not_ suggesting :-) If I understand you
correctly, you are talking about a shelving three-band eq with a level
adjustment of -36 dB and a 24dB/oct band crossover separation (for better
"cuttiness"). My idea is that the mixer is probably easier to build, and
better to use, if you have separate systems for removing frequency bands and
adjusting "sound".

No, it's because many DJs prefer "kill" over "smooth" EQs :)
> Also, I'd think 2 filters per band (and tuning two filters per band)
> would be *more expensive* than one (bandpass) filter per band.
> And more troublesome to tune and fit in the box.


...which was exactly what I was saying... However, you wouldn't need "2
filters per band" with my idea :

You would have 1 normal eq adjusting 3 bands (bass, treble, mid) over a +-
[insert some usably small amount, say 5 to 10 dB] range, and this eq could
be the normal 6 dB/oct separation routine, with fixed crossover frequencies.

Then, you'd have one 24 dB/oct filter with adjustable cutoff, and switchable
between hi and lowpass (and perhaps bandpass, and notch and whatnot).

Hopefully, this would add up to less 6 dB filter blocks than having a 3-band
eq with 24 dB / oct band separation. And imho, it would be much more usable
in a real mixing situation, since you could first adjust the track sound
when you cue up a song, and then when you are actually doing the mix, you
can temporarily use the hipass to kill the bassdrum, while still keeping the
eq adjustments intact. Preferably the pre-listen function would let you (if
you wanted to) pre-listen to the cued track without frequencies cut, so you
would have an easier beat-match situation, while still having the benefits
of bassdrum kills.

Since you can adjust the cutoff frequency of the kill-filter, you get much
better control over what you are killing than with the normal fixed-cutoff
kill-eq setup.

You need to have precision in your fingers :)
> Also, BIG knobs help.


Yup, but this doesn't go against what I'm suggesting. Further, if you have a
shelving-type eq and use it to kill bands, it is difficult to go back to
exactly the same "sound" adjustment settings you had set up before using
those same knobs for killing.

> Not that anyone would hear slight differences on shitty audio setups
> DJs are forced to play on anyways 8P


Now thats a real point, but on the other hand, we're talking "mixer of our
dreams" here, right? :-) Anyway, it makes a real difference on mix-tapes,
which you need to get gigs :-)

> I was thinking of a digitally controlled mixer :)


Hmm, no $200 per channel then, I'm afraid...
>Faders themselves would of course be THE faders.... P&G. no less.

> {well, perhaps for prototype, but I won't rest until those are in my
> box 8) } Though I cringe at the thought of having 6 of these in a
> mixer... or the cost, rather... heh.


Yup, faders are bloody expensive. I, who am only a bedroom DJ, find myself
afraid of using the damn things too roughly...

However, wouldn't it be fairly simple to make a VCA style fader so you could
use any sort of linear mono fader? I guess the usability of that would
depend on the application, but it would cure most problems with having to
choose between glitchy faders and not eating for a month.

Your proposal of making a mixer together sounds very interesting!


Unfortunately, I don't think I'm skilled enough in electronics to design
this sort of thing. I'm more the rip-other-people-schematics sort of guy.

> Tell me what you think of my concept.


If you really want all of that digital stuff, you should probably go
all-software. Just A/D's, then software, then D/A. Digital control over
analog filters seems to me to be a very cost-ineffective way to do things
these days. And hacking it together as a VST plugin to be controlled from a
Behringer rotary MIDI controller seems to be more likely to actually being
done :-) Especially if you're running Live.

In fact, you could probably get this mixing functionality without even
having to write a single line of code! Just download some free VST filters,
a free virtual sound card manager, and set up your MIDI controller properly.

I could take part of the difficult mathematical aspects of this thing.
> I'm a 3rd year maths student :)
> Complex calc is yet to come though :/ 2nd semester of 3rd year, though :)


I don't think neither the analog route or the DSP would require any real
math actually. It's all readily available on the web, except for the
electronics know-how, which doesn't seem to be so much about math as about
intuition :-)

Good luck
/J
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