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Looking to learn more tricks of filtering

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Looking to learn more tricks of filtering

Postby TomChimera » Mon Sep 14, 2020 11:09 am

Hi All,

Some time ago I heard at a trance production studio the Moog filter and a few other amazing analog ones.

Instead of the obvious creative possibilities, the engineer there just used them as a musical low pass filter to clean some digital synths and sounds high end and it sounded amazing to me.

I know these are very complex and companies are creating analog modeled plugin but still i'm inspired to deepen my knowledge and learn some tricks of what can be done with digitals EQ.

I noticed that even though some of the analog filters used were 12 or 24 db, in the EQ plugin 36 db or more sounded closer to these, makes sense?
It seems to me that the regular resonance is not what I'm after, but a broader asymmetrical resonance using peaks is closer.
It seems DMG Equalibrium with a Butterworth mode sounds nice.

The engineer explained to me that some of the analog ones use two stage low pass, any ideas how to do it musically?

People here have so much knowledge :) I would love any tips or if you could guide me to a practical source of in depth techniques of filtering, I'm especially trying to achieve these musical low pass filters.

Thank you very much for any help!!
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Re: Looking to learn more tricks of filtering

Postby Martin Walker » Mon Sep 14, 2020 5:49 pm

TomChimera wrote:
I noticed that even though some of the analog filters used were 12 or 24 db, in the EQ plugin 36 db or more sounded closer to these, makes sense?
It seems to me that the regular resonance is not what I'm after, but a broader asymmetrical resonance using peaks is closer.
It seems DMG Equalibrium with a Butterworth mode sounds nice.

The engineer explained to me that some of the analog ones use two stage low pass, any ideas how to do it musically?

Synth filters tend in general either to have two stages (12dB/octave cutoff) for a more 'brassy' sound, or four (24dB/octave) for purer results, and the classic Moog filter has four. I'd be surprised if the rather more unusual and severe 36dB/octave cutoff was required to emulate classic hardware filters.

Not sure what you're after with 'musical' ideas, but if you've already got DMG Equilibrium then you're off to a fine start - the SOS review is here by the way: https://www.soundonsound.com/reviews/dm ... quilibrium


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Re: Looking to learn more tricks of filtering

Postby TomChimera » Tue Sep 15, 2020 3:51 pm

Thanks Martin!

Martin Walker wrote:Not sure what you're after with 'musical' ideas, but if you've already got DMG Equilibrium then you're off to a fine start - the SOS review is here by the way: https://www.soundonsound.com/reviews/dm ... quilibrium
Martin

Yeah, I should explain what I mean by musical,
When the synths and other sounds, also snares and even high hats, was low passed all the harshness was gone as if by magic :) without the feeling of muffled sound I struggle at times with low pass filters in eq, so I suspected there is some.. magic involved in the shape of the filter, like compensating with a harmonic resonances bellow the cut off point (along with some other stuff)

When you say 2 and 4 stage low pass, do you mean like using actual 2 or 4 instances of low pass one after the other?

I did noticed and wonder if it makes sense: that when I use 2 high pass filters to clean unwanted frequencies it sounds much cleaner than one with higher db per octave...

Thanks!
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Re: Looking to learn more tricks of filtering

Postby James Perrett » Tue Sep 15, 2020 6:16 pm

TomChimera wrote:When you say 2 and 4 stage low pass, do you mean like using actual 2 or 4 instances of low pass one after the other?

Normally that chaining happens inside the plug-in although, if the plug-in only allows a maximum of 2 stages then you'll need to chain multiple instances to get a steeper filter. Sometimes the steepness will be described as "X" order while other filters will talk about a number of dB per octave.

Having had a quick look at the review of Equilibrium I'd say that you can probably do all that you need in one instance of that plug-in although you might want to use more than one filter inside the plug-in.

In this case it is really worth experimenting - you will often find that the filter cut-off frequency is critical to obtaining the sound you want and the right frequency can only be decided by listening.
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Re: Looking to learn more tricks of filtering

Postby TomChimera » Wed Sep 23, 2020 1:14 pm

Thanks for the explanation James!

I would like to also ask about the same subject from a different perspective.
I was working on a film dialogue and the voice was close miked but in the film needed to be outdoor and a few meters away from camera.

I've done gentle low pass and good outdoor impulse response and it worked.

But I wish to learn more about the effects (especially filtering) of distance of sound source.

Can you guide me to an information source that explains what happens to sound through air.

Thank you very much!
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Re: Looking to learn more tricks of filtering

Postby Martin Walker » Wed Sep 23, 2020 2:35 pm

TomChimera wrote:Yeah, I should explain what I mean by musical,
When the synths and other sounds, also snares and even high hats, was low passed all the harshness was gone as if by magic :) without the feeling of muffled sound I struggle at times with low pass filters in eq, so I suspected there is some.. magic involved in the shape of the filter, like compensating with a harmonic resonances bellow the cut off point (along with some other stuff)

Hi again Tom,

Rolling off both top and bottom end on various sounds in your mix can make a lot of sense with electronic productions, as it helps prevent otherwise similar sounds fighting with each other in the mix.

Synths in particular can spit out a pretty wideband signal. For instance, I've got a DSI Prophet 12 keyboard that manages to extend its top filter frequency by an octave compared with previous DSI synths, leading to various comments about it sounding a little harsh and brittle - the advice to back off the filter frequency a little makes perfect sense, and immediately cures this issue.

As for the shape of these high-cut filters, gentle slopes are typically suggested (even 6dB/octave can be enough, while 12dB/octave is perhaps more typical).

When you mention 'compensating with harmonic resonances below the cutoff point', I've never tried doing that with high frequencies, although it's certainly worth a try. However, I do it all the time at the bass end - many lowcut (highpass) filters offer either a flat rolloff, or a slight peak an octave above the cutoff frequency to reinforce the bottom end that's being cut away. Many famous boutique preamps also include this small bass 'hump' to add some subtle warmth.

If you want to get nerdy about it, a Butterworth response is best for lowcut filters, as it rolls off less near the passband (typically 12db/octave works well, especially with a tiny boost an octave above), while Bessel is best for highcut filters, as it keeps phase distortion low over the passband, hopefully leading to a 'sweeter' top end.

I did noticed and wonder if it makes sense: that when I use 2 high pass filters to clean unwanted frequencies it sounds much cleaner than one with higher db per octave...

Once again this is quite feasible - hardware filters tend to involve components spread across multiple stages to provide their overall roll-off characteristic, so each stage is doing its little bit, whereas software filters often (but not always) do it as a single stage. As always, use your ears to decide what sounds best to you.

Hope this helps!


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Re: Looking to learn more tricks of filtering

Postby Martin Walker » Wed Sep 23, 2020 2:39 pm

TomChimera wrote:I wish to learn more about the effects (especially filtering) of distance of sound source.

Can you guide me to an information source that explains what happens to sound through air.

In my opinion, the best candidate to help you learn more is the freeware Proximity plug-in from Tokyo Dawn Labs (https://www.tokyodawn.net/proximity/), which includes realistic control over distance, air absorption, reflections and so on. Its effects can be fairly subtle, but of course you can magnify them as you wish to make the desired effect more obvious.

Image

Its manual provides a concise guide to explain the various distance models, and you can even automate its parameters to gain the effect of sounds moving closer or further away.


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Re: Looking to learn more tricks of filtering

Postby TomChimera » Wed Sep 23, 2020 4:41 pm

Thank you Martin for a lot of very valuable info!!!

I'm reading through the Proximity manual and see it is based on a paper called "ISO 9613-1
Acoustics — Attenuation of sound during propagation outdoors" which I will probably be a good nerd and read it too.

I'm going to do everything you suggested the moment the electricity comes back :)
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Re: Looking to learn more tricks of filtering

Postby blinddrew » Wed Sep 23, 2020 4:58 pm

Any chance of a link to that manual - or a dunce's guide to where it is on the TD page? I couldn't find it. :(
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Re: Looking to learn more tricks of filtering

Postby TomChimera » Wed Sep 23, 2020 5:09 pm

blinddrew wrote:Any chance of a link to that manual - or a dunce's guide to where it is on the TD page? I couldn't find it. :(

Its inside the zip of the downloaded plugin
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Re: Looking to learn more tricks of filtering

Postby blinddrew » Wed Sep 23, 2020 5:14 pm

Ah, thank you. :thumbup:
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Re: Looking to learn more tricks of filtering

Postby TomChimera » Thu Oct 01, 2020 2:22 pm

An update of my journey on this subject :)

In order to remove or soften the high frequencies first I tried mixanalog.com and bounced a test through 2 tape machines (Studer A812 Mk.1, Telefunken M15)
Both were successful to certain extent in reducing the high frequencies and soften them, the Telefunken which have slower speed did it more then the Struder, they sounded beautiful but had a specific sound which I will probably won't want all the time.

I don't have a fast enough internet at the moment to use their website and create proper examples to upload for you to hear, sorry..

Then I went into a rabbit hole for a few days of listening to Chris from Airwindows and trying his plugins to reduce high frequencies like Slew and Acceleration.. Amazing indeed but it wasn't what I was looking for.. (I also tried many other de-harsh style plugins..)

And then.. I'm a bit embarrassed so say, after lots of experiments, I think that the thing I was impressed about in this studio's analog filter wasn't the filter at all... just that he was working in higher Samplerates... :headbang:

Of course I don't know how to explain it but the resampling solved it...
So in my processing I was producing unpleasant sounds in the high frequencies, that he's processing wasn't creating in the first place.. and then when their already there I am trying to reduce them afterwards which doesn't work..


Now I did this experiment, (I know there are many variables or things that could effect this result but still.. I think it's close to what i'm looking for)

1. I took a track at 44khz 32bit float and converted it using Voxengo r8brain to 88khz.
now
File A: 44khz
File B: 88khz

3. In a Cubase session with project setting at 44khz I imported File A, and applied a High Pass with Cubase's eq at 250hz.
And then exported with the same settings, 44khz 32 bit float.

4. In a Cubase session with project setting at 88khz I imported File B, and applied the same High Pass.
And then exported with the same settings, 88khz 32 bit float.

Then I took file B 88khz and converted it back to 44khz using r8brain.

Now:
File A: 44khz
File B: 44khz (went through double conversion and subjectively sounds better)

5. New Cubase session at 44khz and imported 2 files, flip phase, and I believeee this is the harshness I hear.

This leads to a question:
Can you please recommend an affordable eq (I mostly need high and low pass filter) which have oversampling as I need to finish lots of 44khz sessions?

Thank you very much!


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Re: Looking to learn more tricks of filtering

Postby TomChimera » Thu Oct 01, 2020 4:05 pm

I was reading some say the eq's don't need oversampling because they solve it in other ways and people mentioned specifically Fabfilter pro-q so i downloaded the demo, and did they same test. (Span is now normalized so it's actually lower in volume)
Weird results, and to be honest their low latency mode sounds better to me in high samplerates than both of their other methods (linear and natural) in both of the samplerates

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