10Hz - 40KHz What is it good for?

I’ve recently started to use a free EQ plugin, Luftikus by lkjb, https://www.kvraudio.com/product/luftikus-by-lkjb

It has the bands 10Hz, 40Hz, 160Hz, 640Hz, 2,5KHz, and an optional high boost where you can choose between the bands 2,5KHz, 5KHz, 10KHz, 20KHz and 40KHz.

I find it to sound quite good, but i don’t really understand the 10Hz and the 40KHz, what does it really do? If we can only hear frequenzies between 20Hz and 20KHz, then why would i need these bands?

That being said, i do hear these bands when i turn them, so logically it does something to the audible frequenzies too, but then wouldn’t it then work the same as a 20Hz band and a 20KHz with a slightly different curve and lower amplitude?

Are they just trying to confuse me or is there a good reason why these bands are called 10Hz and 40KHz?

BTW i really like the ‘Keep Gain’ function, but not shure of the purpose of the ‘Mastering’ mode…

I guess the values are the cutoff/center points for the associated shelving or peaking filters. You know every filter isn’t on/off by frequency, but will have a certain slope. So the 10 hz filter maybe even reduces/boosts up to 30-40 hz, though not as strong as at 10hz, and might also be very useful for removing rumble that will cost headroom and make dc problems. And the 40 khz filter is probably the cutoff an oversampled shelving filter whose slope will reach down low enough from the cutoff for the effects to still be audible, and the very high cutoff is useful to shift the effected frequencies high enough so only the 15-20khz range is boosted, while the lower modes can also boost lower frequencies?

Ofc. if you need clarity about this that a spectrum analyser and white noise can’t deliver, you’d need to know the actual used filter’s transfer functions to tell for sure, you might ask the developers or look for answers into the open code.

In the plugin’s wiki it says the “mastering mode” would enable discrete steps for the controls, perhaps intended so it will make settings be repeatable by 100% even when “just tweaked by hand”? Also it is written there that the analog mode would work superior with the mastering mode enabled.

It’s a bit weird that it sounds much weeker when turning down the 10Hz knob, slide it up and it seems to sound better, but it might be that my monitors lie a bit here. I often end up with too much of those low frequenzies colliding, but if i filter off too much it tends to end up sounding a bit dull. Think i should read up on the instrument frequency chart in the other thread here, maybe i’ll get a better understanding of how to mix the various sounds…

I always wondered this with this plugin as well. Always thought it sounded great despite the seemingly is freq choices. Interesting to read some explanations for those choices.

Luftikus is actually a pretty simple EQ, just with fixed frequency bands and fixed bandwidth for those bands. That’s not really the news, but here are some more technical and theoretical details: The bandwith is half an octave per band, dynamic range is 15dB (-5 to +10) [edit:]When I measured it myself, it actually looked more like -6 to 18 dB.[/edit]. The chosen frequencies result from most simple math and harmonic theory: 10 * 4 = 40 * 4 = 160 * 4 = 640 * 4 = 2560 (2.5k) - as you can see, each steps has exactly 2 octaves between it. That’s what makes changes fit each other in your ears. Same math goes for the selection of the shelf frequencies, just with factor 2 (1 octave).

Knowing about this, you can recreate the same with a native Renoise EQ. This way you could even setup your very own little mastering EQ variations, with bands like e.g. 12.5 *4 = 50 * 4 = 200 * 4 =… etc. You get the idea.

40KHz in theory doesn’t make much sense at a sampling rate of 44.1KHz. Highest frequency you can achieve is always the half of your sample rate. So usually and IMO you can forget about the 40KHz thing. [edit:] 10Hz and 40KHz might not be audible directly, but can still have and effect on DSP behaviors, like a compressor for example, and become audible indirectly this way. Beside that a band doesn’t exactly end at his theoretic bandwidth. So a change at inaudible frequencies, dependent on its actual filter curve, might still affect audible frequenices, by a filter curve bleeding into frequency areas beyond the theoretical bandwidth.[/edit]

This clip explains a bit more about the effect of “mastering” mode and the other knobs.