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What's the Pultec "Dual knob" idea?
Old 2nd March 2011
  #1
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Sk106's Avatar
 

What's the Pultec "Dual knob" idea?

The Pultec EQ, and its subsequent many imitations, uses a dual knob idea I don't understand fully.
http://www.hestudiotechnik.de/image/...ltec_eqp1a.jpg

Most EQs have a knob that that applies amount of EQ, which is set to zero, and can be turned either way minus or plus. The Pultec idea however, uses 2 knobs for this function - one called Boost and another called Attenuation. The Boost can not apply negative values, and the Attenuation knob can not apply positive values.

So where you can increase the amount of applied EQ with the Boost knob, you can similarly reduce the very same with the Attenuation knob. Is this right?

I can mangle out some abstract own theory as to what benefits this may offer, but I'd like to hear from someone who knows more. What's the idea?
Old 2nd March 2011
  #2
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Quote:
Originally Posted by Sk106 View Post
So where you can increase the amount of applied EQ with the Boost knob, you can similarly reduce the very same with the Attenuation knob. Is this right?
Yep right....dunno why they set it up that way, might be to make the build easier due to a less specific potentiometers being needed.
Having it all on 1 pot one would have needed a dual gang, one 10K log and the other 100K log, with only half the travel each...dunno if that even exists...would have been a custom part for sure.

HOWEVER, due to being able to simultaneous cut AND boost a very interesting EQ curve is produced. This curve (along with the overall sound off course) is basically what then Pultec EQ is famous for. It's a bass boost with a bass cut at the same time ...see below..

Old 2nd March 2011
  #3
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judah's Avatar
 

As far as I understand boost and cut are not at the same frequencies, neither same slope. I use a Pultec (albeit from a UAD) on bass and vocals very often and when you boost a lot of 100Hz it helps to cut them quite a bit too, but to my ears boost and attenuation are not in the same spot frequencies wise. The same goes with kick drum when you boost 60 or 30 a lot and cut them at the same time. It puts a lot of "pressure" in the boost frequency but the cut help to tame the lower frequencies. Now that I think about it it seems that they are both shelving type EQ and playin' with both at the same time mimics a peak type EQ.

I'm sure there will be a more technical reply coming shortly.
Old 2nd March 2011 | Show parent
  #4
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Ah, this good info.

Radiance's graph above is what I know as a Resonant Shelf curve, or Gerzon Shelf curve. I had no idea Pultec enabled this. Possibly, since the Pultec EQ came out quite early, it was about the first to achieve this, which is now available in many modern EQs.

And yes, Judah, I recognize those lines of thought. This is interesting.
Old 2nd March 2011 | Show parent
  #5
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I don't know the exact technical specs behind their EQ, but the cut and boost are not the same. I just play with both knobs until it sounds good, and it doesn't take a whole lot of fiddling to make a Pultec sound good.
Old 2nd March 2011
  #6
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What's the Pultec "Dual knob" idea?

Quote:
Originally Posted by Sk106
Ah, this good info.

Radiance's graph above is what I know as a Resonant Shelf curve, or Gerzon Shelf curve. I had no idea Pultec enabled this. Possibly, since the Pultec EQ came out quite early, it was about the first to achieve this, which is now available in many modern EQs.

And yes, Judah, I recognize those lines of thought. This is interesting.
I seem to remember a couple videos from Tubetech on YouTube where you can hear the boost and cut trick in action.
Old 3rd March 2011 | Show parent
  #7
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vernier's Avatar
It's just the way they designed the circuit, and it seems nobody knows why.
.
.
Old 3rd March 2011 | Show parent
  #8
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I know why




it sounds good
Old 3rd March 2011 | Show parent
  #9
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Quote:
Originally Posted by timlloyd View Post
I know why




it sounds good
Exactly! But so far everyone is right. Both are close but have different frequencies.
Old 3rd March 2011 | Show parent
  #10
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coachz's Avatar
 

When i measured it, there was a multiple of 3, so if I set the cps to 60 hz, the Boost took place at 60 and the atten at 180hz
Old 3rd March 2011 | Show parent
  #11
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8inthemorning's Avatar
The passive fiter was an old Western Electric design.
The Lang uses (about) the same passive design.
But I found it has a clever feature, independent freq spots for bass boost and cut, so combining them you can even make the filter act as a peak/dip, insted of Pultec, which is (essentially) shelving.
Old 3rd March 2011 | Show parent
  #12
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different Q's
Old 3rd March 2011 | Show parent
  #13
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vernier's Avatar
The Pulse Techniques manual says: "Do not attempt to boost and attenuate simultaneously on the low frequencies."
.
.
Old 3rd March 2011 | Show parent
  #14
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Quote:
Originally Posted by vernier View Post
The Pulse Techniques manual says: "Do not attempt to boost and attenuate simultaneously on the low frequencies."
.
.
That's funny!
Old 3rd March 2011 | Show parent
  #15
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I have the Nomad Factory EQP-4, which is clearly inspired by the Pultec EQ.
(pic: http://nomadfactory.com/products/asp...lsize/eqp4.jpg)

When I set the bottom shelf to 100 hz, raise the boost by 6 db and apply 6 db of attenuation, I get a sound which seems very close to the curve mentioned above. The freqs just above 100 hz seems to drop, and the freqs below 100 hz gets boosted. This also shows on a frequency spectrum when I apply it to a white noise.

One can wonder if this was made intentional by Pulse Technologies, or if this was an unexpected benefit.

The statement "Do not attempt to boost and attenuate simultaneously on the low frequencies", was a bit amusing, conflicting. One wonders if it refers to saving other audio equipment or ones own hearing, or if this might create too much tension in the internal circuitry of the Pultec.
Old 3rd March 2011 | Show parent
  #16
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Quote:
Originally Posted by Sk106 View Post

One can wonder if this was made intentional by Pulse Technologies, or if this was an unexpected benefit.

The statement "Do not attempt to boost and attenuate simultaneously on the low frequencies", was a bit amusing, conflicting. One wonders if it refers to saving other audio equipment or ones own hearing, or if this might create too much tension in the internal circuitry of the Pultec.

I can't see how it can damage the unit, but maybe it was to prevent others units in a chain like a mixing desk or a disc cuter (lathe) to get overloaded and distort?
Old 3rd March 2011 | Show parent
  #17
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Fletcher's Avatar
Quote:
Originally Posted by vernier View Post
The Pulse Techniques manual says: "Do not attempt to boost and attenuate simultaneously on the low frequencies."
.
.
Well they obviously never intended it to be used on a kik drum... if they had intended that use they never would have put that caution in the manual!!

There are times when a kik drum is tuned just right that the combination of a bit of boost with simultaneous attenuation can give you a very nice, tight low end that breaks ribs without sending small woofers [like many found in a stock automotive audio system] into a place where you're nearing the end of their excursion capability [which is indeed important... even in the modern "ear bud" world].

Peace.
Old 3rd March 2011 | Show parent
  #18
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Read the manual !!!
Old 18th March 2011 | Show parent
  #19
Quote:
Originally Posted by loopzilla6 View Post
Ok. I'll take a shot at this as I'm almost finished building my second one from scratch (weird geek hobby - I know).
The eq is designed this way on purpose. The frequency of the cut and boost is the same (it only goes through a single capacitor to determine the frequency). What's different is the Q of the cut as opposed to the Q of the boost. The boost Q is fairly wide and the attenuation Q is quite narrow. When you boost wide and simultaneously cut narrow a resonant peak forms on either side of the frequency center creating two more boosted frequency centers roughly an octave above AND below the frequency center. The gain of these "ghost" frequency boosts depend on the amount of simultaneous boost and attenuation settings. More=more.

The net effect is that you get 3 bands of equalization utilizing only one circuit. Phase relationships within a complex waveform don't get screwed up as much and everything "matches" harmonically. Cool huh?

Of course now that I'm almost finished with my reply it occurs that I need to confirm wide boost and narrow cut - it may be the other way around. I'll check and edit my post accordingly, or someone else can jump in and verify.
yeah you had me goin for a sec.
Old 18th March 2011 | Show parent
  #20
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B-sharp's Avatar
 

Quote:
Originally Posted by loopzilla6 View Post
Ok. I'll take a shot at this as I'm almost finished building my second one from scratch (weird geek hobby - I know).
The eq is designed this way on purpose. The frequency of the cut and boost is the same (it only goes through a single capacitor to determine the frequency). What's different is the Q of the cut as opposed to the Q of the boost. The boost Q is fairly wide and the attenuation Q is quite narrow. When you boost wide and simultaneously cut narrow a resonant peak forms on either side of the frequency center creating two more boosted frequency centers roughly an octave above AND below the frequency center. The gain of these "ghost" frequency boosts depend on the amount of simultaneous boost and attenuation settings. More=more.

The net effect is that you get 3 bands of equalization utilizing only one circuit. Phase relationships within a complex waveform don't get screwed up as much and everything "matches" harmonically. Cool huh?

Of course now that I'm almost finished with my reply it occurs that I need to confirm wide boost and narrow cut - it may be the other way around. I'll check and edit my post accordingly, or someone else can jump in and verify.
You're joking right? Your explanation was very good. It also has the effect of sounding like you get to keep a lot of the boost even though you may have negated most of it, which has pretty much already been stated.
Old 18th March 2011 | Show parent
  #21
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Quote:
Originally Posted by loopzilla6 View Post
....it only goes through a single capacitor to determine the frequency

AFAIK, both cut and boost section have their own cap....so they don't share one cap if that's what you meant ?...
Old 19th March 2011 | Show parent
  #22
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stevejackson's Avatar
 

Quote:
Originally Posted by Radiance View Post
AFAIK, both cut and boost section have their own cap....so they don't share one cap if that's what you meant ?...
Yes, the LF BOOST and LF ATTEN circuits are separate from each other (they have their own caps) but are selected using a common 2-section switch. I don't know what loopzilla6 was talking about with respect to Q since these are shelf boost and shelf atten circuits, therefore Q is not a relevant term.

It appears loopzilla6 has removed his original post. At least I don't see it. I just see where it was quoted.
Old 17th July 2012 | Show parent
  #23
Gear Nut
 

[/QUOTE]

it's all math,
as sound is
boost a frequency
attenuate an octave

that way when you add the fundamental waves and have this mathematically perfect pocket available, you get a lush sound that is defined not of boosting improper frequencies, but removing the improper frequencies from the image

the pocket allows you to hear the boosted fundamentals more clearly
and the signature sound was created
& they knew damn well what they had created
Old 20th September 2012
  #24
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JLiRD808's Avatar
Wanna run a PINK PN thru this and put a good spec analyzer or even an RTA at the end...play around with this and see for myself.
Old 16th October 2013 | Show parent
  #25
Quote:
Originally Posted by judah View Post
I seem to remember a couple videos from Tubetech on YouTube where you can hear the boost and cut trick in action.
Here are a few links I found:

Last edited by gsbe; 1st December 2013 at 08:18 AM.. Reason: added one more tutorial link
Old 12th February 2017 | Show parent
  #26
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Quote:
Originally Posted by Sk106 View Post
Ah, this good info.

Radiance's graph above is what I know as a Resonant Shelf curve, or Gerzon Shelf curve. I had no idea Pultec enabled this. Possibly, since the Pultec EQ came out quite early, it was about the first to achieve this, which is now available in many modern EQs.
It has become known by those names, yes. But, interesting to note, Michael Gerzon was attempting to describe the curve on the Pultec which came out when he was just a kid. So, in my research anyway, I still haven't found anything that explains how the Pultec ended up with that ability. Maybe it was serendipity, who knows.
Old 12th February 2017 | Show parent
  #27
Quote:
Originally Posted by Radiance View Post
AFAIK, both cut and boost section have their own cap....so they don't share one cap if that's what you meant ?...
My understanding as well...

2 filters with separate caps on a common rotary switch.
Each filter, cut and boost have their own potentiometer.

A lot of us started splitting that rotary switch so boost and cut can occupy different frequencies. You can make some really nice LF curves that way.
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