What is the technical difference when I make a master highpass/lowpass and on every single channel?

[crazyfiltertweaker]

Some engineers use on every channel a highpass (and maybe lowpass) WITH THE SAME SETTINGS!!! But why???

What is the difference to a highpass on the master output channel?

Yes I know why they use it... to save energy on the lowend which is not audible and I want to use it too... but why using a highpass on every single channel?

Thanks for a TECHNICAL answer!

[Keith99]

Well if you have comressors or other dynamics plug in on a channel it can help to filter out low frequency first

[sergiofrias]

Removing the frequencies below 30 to 50 hz on every track helps to increase the avaiable headroom ,and cleans your mix by removing the "mud" of all those frequencies that you can't hear ,creates better separation ,and allows the tracks to sit better... it also helps with compressors because they don't react to that extreme low freq information ,but with the audible ,musical information...it was also very important when cutting to vinyl ,to prevent jumping of the needle.

[ksandvik]

Many EQs have a visual inspector showing what's happening across the frequency range so you could key in the cut points based on that to avoid unnecessary rumble on the low end and so on. Not that I'm one of the lazy ones that have a default setting as part of a channel strip (Logic Pro X) to set the low-pass on most non-bass SW synths as a starting point --- and I forget to tweak it later.

[Sendy]

Believe it or not, you CAN hear frequencies between 20-50hz, or rather, feel them. I find when they are removed from the entire mix, it tends to sound "blasty" and a bit unreal. Sound is constructed from the bottom up. Highpass absolutely everything you can, except main bass instruments.

[Passing Bye]

Try HPF 100hz on master, that's why

[aciddose]

If you do not understand why this would be done, there is a lot more you do not understand and the best I can say at this point taking into account your comprehension is that it is not possible to explain.

Or in other words there are many, many things you'd need to learn about and the topic is quite complex.

I can describe many elements to give you an impression of the complexity of the topic although you won't be able to follow along if I put all this in a single post.

I'll make a couple follow-up posts to divide these.

[aciddose]

If you have an idea you want to get into a project quickly, you should be familiar with the fact that setting up all your channels, plugins and so on is a lot of work.

When you are forced to do this sort of thing it can destroy your idea/inspiration/muse.

One solution that is widely applied is to create project templates. You might know in advance that for a particular genre you're always going to structure your track in a certain way.

You need three tracks for percs, two for bass, rhythm, ambiance and effects and a lead for example.

This can be taken even further. You can create channel/effects templates. In these sorts of templates taking into account things you don't yet understand many might be motivated to include a high-pass filter.

When applying these sorts of templates to built project templates and applying those templates to an idea, the result will be that every effects configuration contains those identical high-pass filters.

This is just one very small portion of the possible reasons you'd see this. This is only a possible explanation for why these filters may show up identically all over a track. They may not have been manually placed there.

[aciddose]

Consider what happens if you have a DC offset in one of your audio takes.

If you allow this DC to pass through the fader for this track and apply a high-pass filter afterward, it will eliminate the DC as expected.

Now consider what happens when you adjust the fader.

The fader will fade not just the signal, but the DC offset as well which will create thumping effects!

If the high-pass filter were applied pre-fader, this would not occur.

Again, just one very small portion of the potential reasons you'd see these identical high-pass filters applied for every fader.

[aciddose]

Now just imagine I've written the remaining over-nine-thousand posts explaining the whole topic.

...because I won't.

[camsr]

Consider what happens if you have a DC offset in one of your audio takes.

If you allow this DC to pass through the fader for this track and apply a high-pass filter afterward, it will eliminate the DC as expected.

Now consider what happens when you adjust the fader.

The fader will fade not just the signal, but the DC offset as well which will create thumping effects!

If the high-pass filter were applied pre-fader, this would not occur.

Again, just one very small portion of the potential reasons you'd see these identical high-pass filters applied for every fader.

That's enough reason to highpass pre-fader! Although some fader gain controls are smoothed via lowpass filtering, which may not create thumping effects.

[No_Use]

I agree it makes sense doing it pre-fader per track as the example mentioned above.

Though I think it should be also mentioned (and I think that's where the OP is getting at) doing it post-fader (post-FX) there's no technical difference using a 'linear' EQ (I mean not linear phase, but linear in the sense that it doesn't introduce distortion or other non-linearities depending on threshold) for high-/lowpassing on every track with identical settings vs. using the same EQ with identical settings on the master bus.

I've checked this once out of curiousity, there's no difference, it nulls.

[aciddose]

Yes, applying a set of identical linear filters in parallel is identical to applying a single linear filter in series after the linear combination (addition / mixing) of the source channels.

That is unlikely to be where these filters are applied for this reason.

Pre-fader high-pass filters are standard on hardware. Only in software would you not have them Likewise high-pass filters on the input to the channel, between effects, on outputs and so on are also standard in hardware. Rarely do you find any hardware which will pass DC. Only in software do we see signal paths lacking high-pass filters because they require additional processing. That is why in software we need to manually insert them where they would have otherwise existed "naturally" or "by default" in analog gear.

Also as I mentioned this is one of a great many reasons to apply high-pass filters. These reasons are so numerous that it is pointless to bother giving more examples. I can't think of any others which are anywhere near as simple as the ones I've already given.

[aciddose]

That's enough reason to highpass pre-fader! Although some fader gain controls are smoothed via lowpass filtering, which may not create thumping effects.

Actually this is a problem in analog mixers too, although these are analog / continuous. The level of the DC "thump", basically a rounded pulse shaped by the way you turn the knob or slide the fader is entirely based upon how fast you move the control.

In addition to that in hardware often times we're not delivering a control voltage to a VCA like software does, so we can't just "filter" the CV since none exists.

Instead, the signal passes directly through the knob/fader and there can be noise/crackle introduced as the control is adjusted as well. This will be made far more significant if DC is passing through that point. Every resistor generates noise depending upon how much current passes through the resistor, and the size of the resistor. More current (higher voltage / signals) and higher resistance means more noise.

This is why the DC must be removed before any potentiometer (knob/fader) in analog hardware. Just one reason of many.

In software we would generally get other sources of noise. The mouse input isn't entirely smooth, so we get steps generated and the edge of each step produces clicks. Yes, this can be filtered but we'll still end up with a pulse, just a smoother one.

DC elimination is critical in all cases.

[highkoo]

So, this seems to be to the point of OPs question, re: the purpose of 'doubling up' with HP on all channels and master;

.. there's no difference, it nulls.

Seems to make sense. But sometimes it doesnt feel that way, imo.

So, this DC 'thumping' that is being mentioned; Is that just a result when adjusting faders, while letting the DC through?
That was sort of implied, and I cant get my head around how a thump would occur if there were no moving parts.