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Voicing filters

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Voicing filters

Postby Jim U » Thu Jun 21, 2018 9:56 am

I would very much like to see a more detailed explanation of the Hi/Lo EQ filter (also the brightness filter). There are a number of Hi/Lo filters available in DJ and Audio Workstations, but none seem to operate exactly like the HW filter. Is there an article with technical specs or a plug-in with similar characteristics?
Regarding the brightness filter: at what frequency does it break and with what slope?
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Re: Voicing filters

Postby 1961TC4ME » Thu Jun 21, 2018 11:49 am

Hello Jim,

I don't know about the slope part of the brightness adjustment, it does affect the entire overall brightness and is quite noticeable even slightly moving either the entire master slider up and down or each individual slider per pipe. I liken the brightness control to having very similar effects that a treble control would have such as you'd see on an AV receiver. I use the brightness control either if I feel the pipe or pipes sound dull and lack sharpness and detail, or are too bright sounding where I can then dull them down some, again very much like a treble control. Try sliding the controls up and down while you play the stop selected and you will easily be able to hear the effect it has, you can go from mild to wild if you like. :lol:

As far as the hi / low EQ goes, it seems to have a much more subtle and narrow affect on the overall timbre, sometimes I can't even hear the difference, so I generally do not use that control and rely mostly on either the brightness or amplitude controls for voicing. The tuning control can also have some interesting effects.

Perhaps someone here can dive into greater detail as to the effects and when / how to use the hi / low filters.

Marc
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Re: Voicing filters

Postby organsRgreat » Fri Jun 22, 2018 7:43 am

I had occasion to ask a similar question, and received a reply from Martin Dyde which you may find helpful:

viewtopic.php?f=4&t=14792
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Re: Voicing filters

Postby Jim U » Fri Jun 22, 2018 11:32 am

Thank you for both responses. Marc, I have done similar adjustments to pipes that seemed too shrill using the brightness adjustment. I would be one of the first to advise folks to use their ears and pay no attention to the man behind the curtain. Having said that, I believe that understanding how a tool works is important to using it to best advantage.
OrgansRgreat, I read the thread you started a while ago. It provided a lot more information than did the HW manual. I had hoped there would be more discussion or more threads like it. I can make a wild guess as to how the Hi/Lo EQ works but I can't be sure. Maybe if I had a white-noise pipe to voice, I could run the resulting audio into an FFT application and see exactly what it does.
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Re: Voicing filters

Postby organsRgreat » Fri Jun 22, 2018 5:54 pm

Perhaps it would help if the Hauptwerk Eq controls were labelled with more common terms. “Transition frequency” and “transition width” are not descriptions I've come across elsewhere. I'm more used to "High pass", "low pass", "cut off frequency" and "slope".

You could try fixing down a note on the keyboard, then choosing a bright string stop (lots of harmonics), and listening to the effect of the three controls. Reaper - which can be linked directly to Hauptwerk - does have a FFT function; it's one of the effects (called FX). It's possible to play a note on Hauptwerk and look at the frequency spectrum in real time. It jumps about a bit (because Hauptwerk pipes - like real ones - don't produce a steady sound), but you could press Print Screen and look at the resulting image.

Other Digital Audio Workstations (DAWs) probably have a FFT function too, and there must be free-standing applications.

Some theatre organs have a cymbal roll, which would approximate to white noise; you might be able to find a free sample set with one.

This is a case where a diagram would be clearer than any number of words; maybe someone reading this could provide one?
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Re: Voicing filters

Postby josq » Fri Jun 22, 2018 6:32 pm

Note that the brightness filter works on a per-sample basis. It has no fixed cut-off frequency, but it always operates on the harmonics of the note.
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Re: Voicing filters

Postby Jim U » Fri Jun 22, 2018 8:22 pm

Again thanks for continuing this discussion. To OrgansRgreat, I've tried using thin reed pipes to see the effect of Hi/Lo using the real time FFT that comes with Room Equalization Wizard (I think its still free). The harmonics of the reeds and string pipes look quite chaotic and and its difficult to see what the filters are doing. The cymbal roll is a interesting idea. I might have a some TO samples but I'm afraid that it's FFT will be kind of disorganized and very HF rich. I'll look into it. Also the "Blower noise" might work as well.
To josq: Thanks for that information. I had suspected that the filter break frequency of the brightness filter was relative to the fundamental pitch of the pipe to be able to work across the rank. The Hi/Lo must be different since the default "transition frequency" is the same for all pipes.

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Re: Voicing filters

Postby organsRgreat » Sat Jun 23, 2018 3:48 pm

After sleeping on it I realised what I find so puzzling about these filters: why are there THREE parameters? I'd assumed that we were dealing with a simple low-pass filter, in which case only two variables need to be specified - frequency and slope. But what if it's a band-pass filter? Then we do need three parameters - frequency, band width, and the degree of boost or cut. In that context the term “transition width” makes sense - it's synonymous with band width.

Sometimes one has to wait a few days on this forum for someone to notice the topic and provide an answer. My inclination would be to wait a few days, and if we're no further forward I could contact Brett directly and invite him to review the topic. Meanwhile my apologies if what I'm saying here is only what you'd worked out already.
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Re: Voicing filters

Postby jkinkennon » Sat Jun 23, 2018 4:12 pm

With a bandpass filter we control where the amplitude change is centered (frequency), the width of the effect where a high bandwidth means a wider range of frequencies are affected, and the amount of gain or attenuation at the center frequency. It's a challenge to get the three values right without a real-time display of the calculated or measured response.
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Re: Voicing filters

Postby organsRgreat » Sun Jun 24, 2018 7:05 am

I've just re-read the Hauptwerk Installation and User Guide, which says: “The Lo/Hi EQ adjustments allow you to apply a simple low-pass or high-pass parametric EQ (filter) to the pipe”. So it's a parametric EQ, which seems similar to a band pass type. I'm sure jkinkennon is right in saying that “It's a challenge to get the three values right without a real-time display of the calculated or measured response.”

It might help if we could find a piece of software that would plot the response of a parametric eq, so that we could experiment with values then enter them into Hauptwerk. Reaper does have a parametric eq, but unfortunately it doesn't plot a diagram. (I'm using version 4.611 ; maybe later versions do show a diagram). This page looks potentially useful:

https://graphsketch.com/parametric.php

but I don't have time at the moment to experiment with it. Perhaps these thoughts move the discussion forward a little? If anyone finds better software to display a graph of parametric eq values I'd be glad to know about it.
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Re: Voicing filters

Postby Jim U » Sun Jun 24, 2018 10:03 am

I agree with the above comments. If you load up a parametric equalizer, that displays frequency response, into a DAW (I use Adobe Audition a lot.) you can play with the hi and low shelf filters and get band pass and band rejection effects using controls that are similar to those described in the HW guide. I wish I knew exactly what the three HW parameters do. A family of frequency response curves would be very helpful as OrgansRgreat just said.
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Re: Voicing filters

Postby josq » Mon Jun 25, 2018 2:28 am

organsRgreat wrote:After sleeping on it I realised what I find so puzzling about these filters: why are there THREE parameters? I'd assumed that we were dealing with a simple low-pass filter, in which case only two variables need to be specified - frequency and slope. But what if it's a band-pass filter? Then we do need three parameters - frequency, band width, and the degree of boost or cut. In that context the term “transition width” makes sense - it's synonymous with band width.


It is a shelf filter, so you'll need frequency, band width, and boost. It is not a pass filter in the sense that all is passed at certain frequencies and nothing at other frequencies (with a slope in between).

One application could be to eliminate excessive pipe noise (for low-pitched pipes with limited harmonic content)
Last edited by josq on Wed Jun 27, 2018 2:55 am, edited 1 time in total.
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Re: Voicing filters

Postby Jim U » Tue Jun 26, 2018 4:31 pm

I have some HW filter observations that I won't dignify with the term "results".
I used the blower noise from my OLMC sample set. It is very low level and not affected by the overall amplitude control; but if you crank up the brightness filter, it yields usable white noise above 300 Hz or so. Applying the output to the FFT of Room Equalization Wizard you can see a few things.

1. The brilliance filter works like a good old treble control with a break frequency at around C3 where the control appears. Someone had proposed earlier in this thread that this frequency is pitch dependent.
2. The Hi/Lo Filter looks like a band pass filter when the high frequency boost is between 0 and +24 db, and it looks like a simple low pass filter between 0 and -24 db. I refer to these as separate modes.
3. In band pass mode the transition frequency seems to be on the low side of the pass band. As you would expect, it defines the break frequency in the low pass mode.
4. The transition width seems to act like a "q" control, that many parametric filters have, shaping the roll-off and broadening the pass band. It has less effect in the low pass mode
.
Not very precise. It's likely someone else can do a lot better.

PS I just discovered that St. Anne Moseley has a much higher amplitude blower noise "stop" but the Hi/Lo EQ filter doesn't seem to affect it.

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