The title is a bit misleading IMHO. It's more like analog vs digital.
After all, from an electrical point of view they're usually just potentiometers and you can build them either as rotary or as linear potentiometers, but it's just a wiper on a resistive conductive track... (of course there are exceptions that work differently and use hall effect or optical sensors).
The article only talks about the actual circuit that is behind that potentiometer.
Having built some MIDI controllers myself in the past, I noticed that rotary potentiometers allow you to better "decouple" arm/shoulder movements from hand/finger movements. I.e. when you're standing and and holding that knob, It's easier to make precise adjustments when there's a rotary knob you can "hold on to" and slowly twist your fingers, whereas with a linear potentiometer I usually have to keep a finger on the surface next to the knob to "compensate" for involuntary movements coming from my body and arm...
Yes, this is the same for controls in a car. Whoever thought a touch display was the way to go? Our old car had twisty-nobs that you could feel direction already on the grip. No need to look on the symbols what they adjusted. Our "modern" car has still twisty-nobs (we made extra sure of that) but you can't feel the direction because they are perfectly round with a tiny tiny nob for direction. Why do I get the impression development goes backwards?
The hardware is much cheaper, but it is also way cheaper to engineer, and because a touchscreen is a very one-dimensional interface, many questions don't even need to be asked. There's no texture, shape or feedback in a touchscreen, for example.
BMW is a good example. They started putting in that horrendous double wide screen/touch screen removing all buttons (the radio 1-8 shortcuts), temperature, heated seats, fan speed etc onto the screen.
This of course has made their dash design a lot cheaper. The only things remaining are:
Volume (which can be pressed for on/off/play/pause), previous, next, park-anywhere-button, front and rear windshield defroster.
One thing that is amazing about BMW's volume control:
It clicks, but the clicks don't corelate directly with volume change. It depends on how fast you turn the knob. Turn it 5 positions slow = volume += 10. Turn it 5 positions fast = volume += 5. To prevent you from accidently turning it too fast and blowing up your eardrums.
Are there physical controls that mount on a digitizer? E.g. instead of a rotary dial on a potentiometer, the bottom sits on a digitizer that can translate the "touch" event into circular motion. Same with buttons, like with a keyboard membrane, but capacitive. Wouldn't that be cheaper?
That’s not addressing the right issue. Encoders and switches are not the expensive parts. What’s expensive is designing the dashboard with precise holes, before you actually start the manufacturing process, lining up the component with the hole and cap, making sure they actually work etc. Compare that to a dashboard of the new Tesla robo taxi, which basically has a complexity of a TV mount.
But you don't need to line up the holes if you can just plonk the component down anywhere and then program the software with the locations of the components after the fact.
This is also my experience. I'm not a DJ but I perform live electronic music using various MIDI controllers. If I quickly want to add or remove a sound, like a kick drum, to/from the mix, a slider is best. If I need fine control over a parameter, like a low-pass filter frequency, a rotary controller is usually better for the reasons you mentioned.
As alluded to in the article, rotary vs. linear seems to be a proxy for the circuit which actually influences the sound. I would think that anyone claiming "mixers with rotaries always sound better" does not fully understand how they work. There's a lot of those kind of claims in the music scene.
You could have at least three types of linear mixers:
- One where some type of spoon goes back and forth. This would probably just be worse than a rotary mixer though.
- One where the entire "basin" oscillates back and forth like a seesaw, like the machines they have at the blood bank to make sure the blood mixes well with the anticoagulant in the bag(s).
- One where the basin is airtight and vibrated up and down vigorously. I could see this work quite well for dry-ish mixtures of different particles, like if you have flour and sugar together in a container and want them mixed.
I think the third point (vibrating a container to mix different dry particles) is actually the worst way to do it. If the particles have different sizes (or densities technically, I think), they will separate when vibrated, not mix together. If you ever tried to mix Cereals by shaking, you know what I mean. The proper technique is turning over the container continuously to mix the different layers, like in a cement mixer.
Turbulent flow mixers. Typically operated in industrial processess where two or more products are pumped through a specially shaped manifold which causes intentional turbulence in the material to mix the different streams. Contrary to blenders or planetary mixers these operate in a continous fashion not on a batch-by-batch basis.
Even when started reading I still didn't know what it was about. When DJs were mentioned I thought it was something related to turntables, as they are the rotary thing? Vinyl was mentioned in few places so it must be it? Then audiophiles were mentioned which is super strange since audiophiles don't use mixers at all. You're not mixing anything when you listen to music.
Turned out it's just about rotary vs linear potentiometers. Or I misunderstood everything.
How an entire article about rotary mixers fails to mention Rane or their legendary MP2016 mixer is wild.
It became one of the most commonly available rotary mixers, was the house mixer for many NYC clubs, and one of the mixers commonly found on tech riders of DJs who were the last to transition to CDJs.
Random bit of trivia: if you see old school photos or videos of rotary mixers in American clubs, sometimes it wasn't actually the Rane MP2016, but the Phazon SDX 3700: https://www.integralsound.com/sdx-3700-mixer It was the house mixer for Tunnel/Limelight.
Any headline with a question...
Of course it depends on what you want to do and what you are used to.
Technically, regardless of the rest of the product design there are high quality potentiometers available both as linear faders or rotary knobs. I guess dirt is more likely to get into a linear fader and make it scratchy - especially in a club environment.
You can't do (or it is much more involved) to do cuts with rotary knobs. So they serve only the DJ who does slow mixes, while with faders you can do both.
Is there anything that compares to their absolute dominance? Every one is using their CDJs these days. Occasionally people still break out the steel wheels but Pioneer seem to have completely captured the market.
Inertia, plus in the grand scheme of things CDJs aren’t too expensive for clubs.
Two CDJs cost less than weekend’s worth of personnel for a small club even.
If you’re a DJ that’s just starting out, it suck’s a little though. Usually you’ll start out on Native Instruments’ Traktor S2/S4 or Pioneer’s cheaper DDJ, and for your first club set you arrive early so you can familiarize yourself with the quirks of the CDJs. Or find a buddy with a CDJ home setup that you can practice on.
Allen & Heath Xone 96 (or previous 92 model) mixers are very popular in the techno world.
Pioneer DJMs have dozens of FX combinations to aid with fast/fancy transitions, whereas techno/trance (and similar) genres that rely on long smooth blends like the extra EQ channel and filters.
I don't know any hip-hop DJs that use Xones?
The Xones are also analogue vs digital Pioneer mixers which also plays a part in audio quality, especially if the source is analogue (vinyl, rack modules, etc).
I'm happy with my Pioneer DJM-750mk2... but also happy to exchange a kidney for Xone:96 :-)
A big reason is the Rekordbox software used to manage song libraries. Another is standardization - DJs move from club to club and encounter the same hardware setup. They are very well built, work in rain, ...
Today you also have influencers which are DJ-ing, but they don't have the skills, so either they have a pre-recorded mix or just use the CDJ auto-mixing features. Having a standard device they know how to operate is again critical.
I actually have a Taula 2 and a Xone 92 at home. I prefer the Taula 2, due to the simplicity and the fact that it has an isolator. The Xone 92 has a four band IQ and a filter, which I like a lot, but I have the impression that all the bells and whistles take a toll on the quality. At least in a home listening setup.
Totally agree. But I guess most audio software expect you to map those rotary potentiometers to actual midi controller with infinite rotary encoder and the UI serves as a way to see the status.
Having said that you can totally map a physical rotary encoder to a linear one in the software so this is not a good excuse.
If it's operated by a mouse you're not sure where to click and hold, and how it will react when you move mouse in which direction.
I assume you're using it a lot and then it's intuitive. For novice it's not. If I click on bottom part will it operate in another direction compared with clicking on top part? Or what about if I click on left or right edge? Can I also move mouse up-down and left-right or is only one direction allowed? Is mouse-up turning knob up or down? Are these rules same in all software or knob behaves slightly different everywhere? I have no idea for any of that except if I try and see. And since I rarely use them it's always a source for frustration.
Especially compared to linear slider which is impossible to misunderstand and you can't operate in it wrong way.
> Are these rules same in all software or knob behaves slightly different everywhere?
They're different everywhere.
My own opinion is that on-screen knobs for audio-type work can be fine as long as one can grab any part of the knob with the mouse and adjust it by moving the mouse up and down (er...well, physically forward and back).
But things are not always this way so it seems that opinions vary.
Nailed it. Even if the knob worked like a real knob, it would suck. I'm supposed to drag the cursor around in a circle? What a fussy PITA. And what is the hittable zone for that? The very edge? The center to the edge? Some slop area beyond the edge too?
Yeah, I see how it can be confusing for novices. But learning curve aside, there is something other than just looks that kept this UI pattern alive all these decades.
How I see it [1], absolute values don't matter audio software, except when working with loudness compliance or some very technical things. What's important is how things sound, and it's generally a bad practice relying on UI metering to dial in sound in most cases. The typical audio work involves fine tuning parameters until things feel right. In UX terms, relative parameter tuning is the most common kind of interaction, and sliders absolutely suck balls at it, in my humble opinion.
Linear sliders actually have more inconsistencies across implementation than knobs, that have converged to more or less the same pattern. E.g. some sliders reset value if you click in the middle of it, at which point all prior tuning is lost - this is super annoying and I hate it. Others operate in relative mode and they're similarly intuitive in regards to which direction they should operate depending on slider orientation (should horizontal slider change its value with up-down movement? should interaction range extend beyond slider length?). Also, such sliders are identical to knobs, essentially, but take more screen space.
So, in a a nutshell, knobs are superior for fine tuning, which is 90% of all audio software interactions.
1. I'm not a professional, but I have clocked in thousands of hours into DAWs and other related software over the years as a hobby, also I played on a few local gigs and made some simple audio software.
I think knobs specifically target computer novices, with the software publisher thinking that a computer-appropriate control would be somehow baffling or confusing to people who "know knobs."
The shortcomings of sliders you mention are down to shitty implementations. I have never seen a slider that resets if you click in the middle of it; that's a crap UI. It's common to simply have a little reset button next to a variable control.
"should horizontal slider change its value with up-down movement? should interaction range extend beyond slider length?"
Of course not to both. I've never seen either one of those behaviors.
Knobs are bad for fine adjustment, because the closer to the center you click and drag, the more drastic the adjustment per pixel of dragging.
> I think knobs specifically target computer novices
I don't think this is the case. Knobs are very convenient and more compact than sliders, in my personal opinion (I did a lot of audio work in the past). Manufacturers create realistic UIs because they sell better due to various perception biases (brain interprets something as sounding better if it has a UI resembling an SSL console, etc.).
> Knobs are bad for fine adjustment, because the closer to the center you click and drag, the more drastic the adjustment per pixel of dragging.
This is incorrect. In almost all pro audio software knobs are operated with a vertical drag movement. Holding a modifier key increases movement precision. I definitely have seen the behaviour you described, but it was maybe in a very old VST plugin probably two decades ago.
> The shortcomings of sliders you mention are down to shitty implementations.
Sadly, it's quite common. Three modern examples from the top of my head: Renoise, Reaper, Max/MSP. Unlike knobs, sliders can be quite random in their implementation.
> It's depressing that audio software still widely subjects users to this skeuomorphic failure
May I ask, which software are you using? The original argument suggests we're discussing pro audio, but I can't recall seeing neither angular knobs, nor 'small [reset] buttons nearby sliders', and I've used a lot of different DAWs and plugins, so maybe we're talking about something else here?
As someone which designed such audio UIs with knobs, it's not because skeuomorphic was the target, it's because there is no better way to fit 50 controls in a small space while being able to see them all at the same time.
There's plenty of UI that presents drop-down (or pop-up) sliders.
I will say, though, that a circle whose perimeter is partially filled in is a space-efficient way to depict the current value vs. the total range available.
The title is a bit misleading IMHO. It's more like analog vs digital. After all, from an electrical point of view they're usually just potentiometers and you can build them either as rotary or as linear potentiometers, but it's just a wiper on a resistive conductive track... (of course there are exceptions that work differently and use hall effect or optical sensors).
The article only talks about the actual circuit that is behind that potentiometer.
Having built some MIDI controllers myself in the past, I noticed that rotary potentiometers allow you to better "decouple" arm/shoulder movements from hand/finger movements. I.e. when you're standing and and holding that knob, It's easier to make precise adjustments when there's a rotary knob you can "hold on to" and slowly twist your fingers, whereas with a linear potentiometer I usually have to keep a finger on the surface next to the knob to "compensate" for involuntary movements coming from my body and arm...
Yes, this is the same for controls in a car. Whoever thought a touch display was the way to go? Our old car had twisty-nobs that you could feel direction already on the grip. No need to look on the symbols what they adjusted. Our "modern" car has still twisty-nobs (we made extra sure of that) but you can't feel the direction because they are perfectly round with a tiny tiny nob for direction. Why do I get the impression development goes backwards?
> Whoever thought a touch display was the way to go?
A lot of people talk about as it was primarily a design decision, but I suspect touch screen controls are the cheapest one out there right now.
The hardware is much cheaper, but it is also way cheaper to engineer, and because a touchscreen is a very one-dimensional interface, many questions don't even need to be asked. There's no texture, shape or feedback in a touchscreen, for example.
BMW is a good example. They started putting in that horrendous double wide screen/touch screen removing all buttons (the radio 1-8 shortcuts), temperature, heated seats, fan speed etc onto the screen.
This of course has made their dash design a lot cheaper. The only things remaining are:
Volume (which can be pressed for on/off/play/pause), previous, next, park-anywhere-button, front and rear windshield defroster.
One thing that is amazing about BMW's volume control:
It clicks, but the clicks don't corelate directly with volume change. It depends on how fast you turn the knob. Turn it 5 positions slow = volume += 10. Turn it 5 positions fast = volume += 5. To prevent you from accidently turning it too fast and blowing up your eardrums.
Are there physical controls that mount on a digitizer? E.g. instead of a rotary dial on a potentiometer, the bottom sits on a digitizer that can translate the "touch" event into circular motion. Same with buttons, like with a keyboard membrane, but capacitive. Wouldn't that be cheaper?
That’s not addressing the right issue. Encoders and switches are not the expensive parts. What’s expensive is designing the dashboard with precise holes, before you actually start the manufacturing process, lining up the component with the hole and cap, making sure they actually work etc. Compare that to a dashboard of the new Tesla robo taxi, which basically has a complexity of a TV mount.
But you don't need to line up the holes if you can just plonk the component down anywhere and then program the software with the locations of the components after the fact.
Especially when sisterly countries with sisterly regulations are taken into account.
This is also my experience. I'm not a DJ but I perform live electronic music using various MIDI controllers. If I quickly want to add or remove a sound, like a kick drum, to/from the mix, a slider is best. If I need fine control over a parameter, like a low-pass filter frequency, a rotary controller is usually better for the reasons you mentioned.
As alluded to in the article, rotary vs. linear seems to be a proxy for the circuit which actually influences the sound. I would think that anyone claiming "mixers with rotaries always sound better" does not fully understand how they work. There's a lot of those kind of claims in the music scene.
Though it's easy to see why linear potentiometers make sense if you want to adjust multiple at the same time.
However in these modern days with motor driven potentiometers, I guess it is less of a big deal.
That’s not generally the use case for DJ mixers.
True, but not all mixers are DJ mixers.
Oh. I first thought it would be about blenders and thought "what other principles would be there?"
You could have at least three types of linear mixers:
- One where some type of spoon goes back and forth. This would probably just be worse than a rotary mixer though.
- One where the entire "basin" oscillates back and forth like a seesaw, like the machines they have at the blood bank to make sure the blood mixes well with the anticoagulant in the bag(s).
- One where the basin is airtight and vibrated up and down vigorously. I could see this work quite well for dry-ish mixtures of different particles, like if you have flour and sugar together in a container and want them mixed.
I think the third point (vibrating a container to mix different dry particles) is actually the worst way to do it. If the particles have different sizes (or densities technically, I think), they will separate when vibrated, not mix together. If you ever tried to mix Cereals by shaking, you know what I mean. The proper technique is turning over the container continuously to mix the different layers, like in a cement mixer.
Turbulent flow mixers. Typically operated in industrial processess where two or more products are pumped through a specially shaped manifold which causes intentional turbulence in the material to mix the different streams. Contrary to blenders or planetary mixers these operate in a continous fashion not on a batch-by-batch basis.
Even when started reading I still didn't know what it was about. When DJs were mentioned I thought it was something related to turntables, as they are the rotary thing? Vinyl was mentioned in few places so it must be it? Then audiophiles were mentioned which is super strange since audiophiles don't use mixers at all. You're not mixing anything when you listen to music.
Turned out it's just about rotary vs linear potentiometers. Or I misunderstood everything.
You are not the only one.
How an entire article about rotary mixers fails to mention Rane or their legendary MP2016 mixer is wild.
It became one of the most commonly available rotary mixers, was the house mixer for many NYC clubs, and one of the mixers commonly found on tech riders of DJs who were the last to transition to CDJs.
Random bit of trivia: if you see old school photos or videos of rotary mixers in American clubs, sometimes it wasn't actually the Rane MP2016, but the Phazon SDX 3700: https://www.integralsound.com/sdx-3700-mixer It was the house mixer for Tunnel/Limelight.
Any headline with a question... Of course it depends on what you want to do and what you are used to.
Technically, regardless of the rest of the product design there are high quality potentiometers available both as linear faders or rotary knobs. I guess dirt is more likely to get into a linear fader and make it scratchy - especially in a club environment.
Seems like ad copy for the recently-released Alpha Theta Euphonia.
Seems like ad copy for classic Veblen pricing, with rotaries being sold as a status symbol.
They cost more than most studio mixers with far more channels and features.
The margins on these things must be insane - probably 5-10X between production cost (including R&D) and end-user price.
What, no discussion of knob size, knurl, and operating torque?
At this point it's mostly a user interface problem.
Hello to other UK readers having a little chuckle to themselves.
Hello, and thank you.
You can't do (or it is much more involved) to do cuts with rotary knobs. So they serve only the DJ who does slow mixes, while with faders you can do both.
There's some that have a button for cut, same for EQ kills
Can’t by design. It’s a different process. You can’t get the same smooth transitions as easily with the light faders on pioneer djms (the standard).
Is there anything that compares to their absolute dominance? Every one is using their CDJs these days. Occasionally people still break out the steel wheels but Pioneer seem to have completely captured the market.
Inertia, plus in the grand scheme of things CDJs aren’t too expensive for clubs.
Two CDJs cost less than weekend’s worth of personnel for a small club even.
If you’re a DJ that’s just starting out, it suck’s a little though. Usually you’ll start out on Native Instruments’ Traktor S2/S4 or Pioneer’s cheaper DDJ, and for your first club set you arrive early so you can familiarize yourself with the quirks of the CDJs. Or find a buddy with a CDJ home setup that you can practice on.
Allen & Heath Xone 96 (or previous 92 model) mixers are very popular in the techno world.
Pioneer DJMs have dozens of FX combinations to aid with fast/fancy transitions, whereas techno/trance (and similar) genres that rely on long smooth blends like the extra EQ channel and filters.
I don't know any hip-hop DJs that use Xones?
The Xones are also analogue vs digital Pioneer mixers which also plays a part in audio quality, especially if the source is analogue (vinyl, rack modules, etc).
I'm happy with my Pioneer DJM-750mk2... but also happy to exchange a kidney for Xone:96 :-)
HÖR use A&H mixers when people play vinyl on their YouTube channel. It’s very noticeable, especially for the proggy stuff!
Technics SL-1200/1210 mk2 had a similar dominance for maybe a couple of decades, I think
A big reason is the Rekordbox software used to manage song libraries. Another is standardization - DJs move from club to club and encounter the same hardware setup. They are very well built, work in rain, ...
Today you also have influencers which are DJ-ing, but they don't have the skills, so either they have a pre-recorded mix or just use the CDJ auto-mixing features. Having a standard device they know how to operate is again critical.
Yeah, maybe if that DJ ignores the crossfader.
I actually have a Taula 2 and a Xone 92 at home. I prefer the Taula 2, due to the simplicity and the fact that it has an isolator. The Xone 92 has a four band IQ and a filter, which I like a lot, but I have the impression that all the bells and whistles take a toll on the quality. At least in a home listening setup.
Anyways, it’s not the knobs that make the sound…
Xones are more like specialist precision tools that can be tweaked to a fine degree.
Pioneers have many options to quickly bail out of a train wreck mix!
Not in a computer UI.
It's depressing that audio software still widely subjects users to this skeuomorphic failure, trying to do everything with on-screen "knobs." Ugh.
Totally agree. But I guess most audio software expect you to map those rotary potentiometers to actual midi controller with infinite rotary encoder and the UI serves as a way to see the status.
Having said that you can totally map a physical rotary encoder to a linear one in the software so this is not a good excuse.
Why do you think on-screen knobs is a failure? I personally find them very convenient for the purpose.
If it's operated by a mouse you're not sure where to click and hold, and how it will react when you move mouse in which direction.
I assume you're using it a lot and then it's intuitive. For novice it's not. If I click on bottom part will it operate in another direction compared with clicking on top part? Or what about if I click on left or right edge? Can I also move mouse up-down and left-right or is only one direction allowed? Is mouse-up turning knob up or down? Are these rules same in all software or knob behaves slightly different everywhere? I have no idea for any of that except if I try and see. And since I rarely use them it's always a source for frustration.
Especially compared to linear slider which is impossible to misunderstand and you can't operate in it wrong way.
> Are these rules same in all software or knob behaves slightly different everywhere?
They're different everywhere.
My own opinion is that on-screen knobs for audio-type work can be fine as long as one can grab any part of the knob with the mouse and adjust it by moving the mouse up and down (er...well, physically forward and back).
But things are not always this way so it seems that opinions vary.
Nailed it. Even if the knob worked like a real knob, it would suck. I'm supposed to drag the cursor around in a circle? What a fussy PITA. And what is the hittable zone for that? The very edge? The center to the edge? Some slop area beyond the edge too?
Just no.
Yeah, I see how it can be confusing for novices. But learning curve aside, there is something other than just looks that kept this UI pattern alive all these decades.
How I see it [1], absolute values don't matter audio software, except when working with loudness compliance or some very technical things. What's important is how things sound, and it's generally a bad practice relying on UI metering to dial in sound in most cases. The typical audio work involves fine tuning parameters until things feel right. In UX terms, relative parameter tuning is the most common kind of interaction, and sliders absolutely suck balls at it, in my humble opinion.
Linear sliders actually have more inconsistencies across implementation than knobs, that have converged to more or less the same pattern. E.g. some sliders reset value if you click in the middle of it, at which point all prior tuning is lost - this is super annoying and I hate it. Others operate in relative mode and they're similarly intuitive in regards to which direction they should operate depending on slider orientation (should horizontal slider change its value with up-down movement? should interaction range extend beyond slider length?). Also, such sliders are identical to knobs, essentially, but take more screen space.
So, in a a nutshell, knobs are superior for fine tuning, which is 90% of all audio software interactions.
1. I'm not a professional, but I have clocked in thousands of hours into DAWs and other related software over the years as a hobby, also I played on a few local gigs and made some simple audio software.
I think knobs specifically target computer novices, with the software publisher thinking that a computer-appropriate control would be somehow baffling or confusing to people who "know knobs."
The shortcomings of sliders you mention are down to shitty implementations. I have never seen a slider that resets if you click in the middle of it; that's a crap UI. It's common to simply have a little reset button next to a variable control.
"should horizontal slider change its value with up-down movement? should interaction range extend beyond slider length?"
Of course not to both. I've never seen either one of those behaviors.
Knobs are bad for fine adjustment, because the closer to the center you click and drag, the more drastic the adjustment per pixel of dragging.
> I think knobs specifically target computer novices
I don't think this is the case. Knobs are very convenient and more compact than sliders, in my personal opinion (I did a lot of audio work in the past). Manufacturers create realistic UIs because they sell better due to various perception biases (brain interprets something as sounding better if it has a UI resembling an SSL console, etc.).
> Knobs are bad for fine adjustment, because the closer to the center you click and drag, the more drastic the adjustment per pixel of dragging.
This is incorrect. In almost all pro audio software knobs are operated with a vertical drag movement. Holding a modifier key increases movement precision. I definitely have seen the behaviour you described, but it was maybe in a very old VST plugin probably two decades ago.
> The shortcomings of sliders you mention are down to shitty implementations.
Sadly, it's quite common. Three modern examples from the top of my head: Renoise, Reaper, Max/MSP. Unlike knobs, sliders can be quite random in their implementation.
> It's depressing that audio software still widely subjects users to this skeuomorphic failure
May I ask, which software are you using? The original argument suggests we're discussing pro audio, but I can't recall seeing neither angular knobs, nor 'small [reset] buttons nearby sliders', and I've used a lot of different DAWs and plugins, so maybe we're talking about something else here?
The scroll wheel usually works for these as well.
As long as they support dragging up and down as a way to make them rotate
As someone which designed such audio UIs with knobs, it's not because skeuomorphic was the target, it's because there is no better way to fit 50 controls in a small space while being able to see them all at the same time.
There's plenty of UI that presents drop-down (or pop-up) sliders.
I will say, though, that a circle whose perimeter is partially filled in is a space-efficient way to depict the current value vs. the total range available.