How Tone controls work

[darwin-bass]

On a lot of threads, I end up trying to explain to people how passive tone controls on basses work (spoiler - they don't work like you think they do). Though they are simple circuits, the reactive nature of the pickups feeding them results in behavior you wouldn't really expect - they don't just "turn down the treble". Anyway, having designed circuits and other pro audio stuff for a living, Spice simulations (they way we predict circuit behavior before building prototypes) are in my wheelhouse. I won't go into tall the details of this (you need to characterize the pickups, which is a non- trivial task, but still not rocket science). Anyway, the point is, we'll be looking at the electrical behavior of passive tone circuits, which are part of the sound of a bass (pickup location is move complex, but also something you can simulate well - that's for another day).
...

And this is why I wish there was a "like" button at the top of a post. Even before reading the whole post I'm already 100% invested. Pre-Like all the way!!!

 

[darwin-bass]

Now that I've read (and understood) it I love it even more.

 

[darwin-bass]

If the PU is wired directly the output jack, how do things change?

I assume the resonance peak is still there, just smaller in amplitude and higher in frequency?

 

[micguy]

If the PU is wired directly the output jack, how do things change?

I assume the resonance peak is still there, just smaller in amplitude and higher in frequency?

Doing that takes the load from the tone pot and the volume pot out of the circuit. The pickup's inductance is still there, the loading capacitances are all still there, so....the resonance will be at the same frequency, but the amplitude (the height of the peak) will go up.

 

[darwin-bass]

Doing that takes the load from the tone pot and the volume pot out of the circuit. The pickup's inductance is still there, the loading capacitances are all still there, so....the resonance will be at the same frequency, but the amplitude (the height of the peak) will go up.

Making the bass sound brighter.

Makes sense.

 

[fishdude101101]

They all have flat curves in the lows and low mids. In the upper mids, and highs, they all have a resonance - usually a peak, though it can be very damped and not stick up much, if at all, in some cases.

There are two primary things at play that affect the perception of things:

1) Psychoacoustics. If you have a big whopping peak in they upper mids, you will end up turning down the volume, and the perception is less lows or low mids - it's just a distraction thing. If you're hearing a "scooped pickup", it's most likely this at work.

If there are two pickups, and you're hearing a scoop, or you're playing through an amp (especially a Fender), it's very likely the scoop you're hearing has nothing to do with the pickup - there are very real "scoops" out there that have to do with mixing pickups and tone stacks in amps..

2) Non - linearities. This is more subtle, but it is real. When you have a magnetic pickup on one side of a string, and the string movement is a significant fraction of the nominal distance, the waveform you get out is not strictly speaking a reflection of the string's movement - it is distorted. Let's say the string is an eight of an inch away, and the string is moving half of that. At its closest, the string is now 1/2 the distance it is at rest (a factor of 2), and at its furthers, it is 1 1/2 times further - a factor of 1.5, not 2. Given that, the waveform will be squashed more on one side than the other. It's assymetrical distortion, and will give you some added stuff - primarily second harmonic of what is there. There are almost always harmonic on the string, so it will give you a bit of second harmonic of those harmonics in addition to the second harmonic of the fundamental, etc. - it creates some additional lower mid stuff. This is, in most cases, pretty subtle, but it is real. If you back off the pickup (lower it away from the strings), it reduces this effect.

It would help my understand if we had some sort of definition here of lows low mids, high mid, treble. I get what your saying but then I've seen some people supposedly posting stuff that shows differences in pickups.

So what your saying is the difference is the placement of the resonant peak and overall output?

 

[Timmy-Watts]

Does the resistor thing mentioned earlier, that takes out the low mid boost at the end of the taper, is that what Fender’s “greasebucket” tone circuit did? They described it as a more even taper of highs and without the bump in midrange resonant peak and mud when rolled back.

 

[micguy]

Does the resistor thing mentioned earlier, that takes out the low mid boost at the end of the taper, is that what Fender’s “greasebucket” tone circuit did? They described it as a more even taper of highs and without the bump in midrange resonant peak and mud when rolled back.

I have stared at and have simulated that circuit, and I'm not really sure what they were trying to optimize. I do different things to deal with the effects at and around min tone, and I can tell you what I did and why. The Greasebucket, I've never understood why, or seen or heard anyone describe what the point was.

 

[StayLow]

It would help my understand if we had some sort of definition here of lows low mids, high mid, treble. I get what your saying but then I've seen some people supposedly posting stuff that shows differences in pickups.

So what your saying is the difference is the placement of the resonant peak and overall output?

This might help?

Many here will use “Low Mids” to mean what’s labelled below as “Upper Bass” and “Mids” to also include what’s labelled below as “Lower Midrange” - totally fine and usually totally clear by context of the comment or discussion - while descriptions of frequency ranges are otherwise consistent with this:

 

[sikamikanico]

This might help?

Many here will use “Low Mids” to mean what’s labelled below as “Upper Bass” and “Mids” to also include what’s labelled below as “Lower Midrange” - totally fine and usually totally clear by context of the comment or discussion - while descriptions of frequency ranges are otherwise consistent with this:


View attachment 5391525

Yeah, that seems about right in general. But many of us have used different ranges/cutoffs for bass guitar, right or wrong. For me, upper/high mids were about 800 Hz. I have since learned that this is not how others label the frequencies, so I’m trying to be more careful with my language.

I think a lot of this comes from amp design, where they label the frequencies quite inconsistently. For many of us, this was the entry point into these discussions. I recall looking up the frequencies behind the labels on my amp, and those kinda stuck with me. Just for curiosity, I looked up Mesa’s current labels for the Subway amp, and it seems like their “high mids” are at 400 Hz, heh.


Back to discussion of pickups and tone controls - I think what the figure above shows as upper mids and presence are really key for bass sound. Our ears are particularly sensitive in that range. That’s where we often find pickup resonant frequencies, and those dominate the character of the tone. So turning down the tone control is heard quite audibly, and while it technically doesn’t reduce the treble, it sounds darker and darker…

interesting side-point. I noticed that some very hifi pickups stay flat very far up into the treble range, and may have a very low peak (amplitude). While technically that’s a brighter pickup, it can sound darker because it doesn’t have the peak in that most audible range.

 

[Jerry Catanescu]

Well, "treble" as it pertains to guitar and bass pickups is something in the range of perhaps 4k to certainly no higher than 7 or 8k. The combination of pickups, amp and cab has no meaningful output much above that. We'd probably call this same range upper mids if talking about a hi-fi amp. As an example, having built a Rockman-like guitar effect, I can assure you that there's essentially nothing above 5k in its output. Both clean and distorted. What we hear as "treble" in the Rockman sound is actually a peak at around 3.5kHz.

 

[micguy]

interesting side-point. I noticed that some very hifi pickups stay flat very far up into the treble range, and may have a very low peak (amplitude). While technically that’s a brighter pickup, it can sound darker because it doesn’t have the peak in that most audible range.

I have characterized close to 100 different bass guitar pickups at this point, and so far, I haven’t encountered any I’d call “hi fi”. It is technically possible - using much fewer winds would reduce the inductance to where you would have flat response, but that would also give you a LOT less output. I think what people consider “hi fi” pickups are those with a little more bandwidth and a little higher peak - they’ve got a bit more high mids and treble, but not as much as you think. A pickup without rolloff at 10 KHz would most likely be very harsh sounding.

 

[sikamikanico]

I have characterized close to 100 different bass guitar pickups at this point, and so far, I haven’t encountered any I’d call “hi fi”. It is technically possible - using much fewer winds would reduce the inductance to where you would have flat response, but that would also give you a LOT less output. I think what people consider “hi fi” pickups are those with a little more bandwidth and a little higher peak - they’ve got a bit more high mids and treble, but not as much as you think. A pickup without rolloff at 10 KHz would most likely be very harsh sounding.

yeah, for sure, “hi-fi” by bass pickup standards it was more a comment about how we perceive sound, which can create some confusion.

 

[sunbeast]

I have characterized close to 100 different bass guitar pickups at this point, and so far, I haven’t encountered any I’d call “hi fi”. It is technically possible - using much fewer winds would reduce the inductance to where you would have flat response, but that would also give you a LOT less output. I think what people consider “hi fi” pickups are those with a little more bandwidth and a little higher peak - they’ve got a bit more high mids and treble, but not as much as you think. A pickup without rolloff at 10 KHz would most likely be very harsh sounding.

The old Seymour Duncan "Active EQ" active pickups with the three dipswitches on the top used the dipswitches to choose the resonant peak of the pickups, apparently with a pretty large peak at around 10khz with none of the switches selected (this based on the graphs in their own literature)- its actually the next peak down (around 3-4khz)that sounded the brightest though through my gear (presumably because there just isn't much happening on a bass in between those two settings). Those are by far the brightest bass pickups I've ever used, and definitely can get harsh and thin on some settings without using extra EQ after. I love them, but they would definitely not be a typical bassist's cup o tea at many settings (which is presumably why they just chose a fixed setting on their active pickup successors)

 

[sunbeast]

Fantastic work @micguy !

I’m interested in how multi-cap units (like the ToneStyler) look. I think I know, but I could be wrong.

A cool thing to play with is using something like a Tonestyler combined with a "depth" pot (I had good luck with a 50Kohm pot), allowing you to shift the resonant frequency and adjust the height of the peak at different frequencies.

 

[Riff Ranger]

Even though I have always considered the passive tone knobs on my instruments purely decorative I really appreciate this post, and @micguy generally. It does have me wondering if I should ditch passive tone knobs entirely on my darker-sounding passive basses, as I really like a whole lot of 1–2khz and I really don’t like steel outer wraps on my roundwound strings.

 

[XLunacy]

Still waiting for this gem of a thread to be stickied 99% of basses have a tone control, yet most people (fewer now I guess!) do not know how they work.

I guess it could easily replace the "EMG Geezer Butler Pickup Solutions for J pickup hum link" thread dealing with a bad batch of EMG pickups that happened 8 years ago.

Please?

 

[sikamikanico]

Still waiting for this gem of a thread to be stickied 99% of basses have a tone control, yet most people (fewer now I guess!) do not know how they work.

I guess it could easily replace the "EMG Geezer Butler Pickup Solutions for J pickup hum link" thread dealing with a bad batch of EMG pickups that happened 8 years ago.

Please?

Do we need to collect 5000 signatures to get a sticky, or what? who makes the decision? Do we need to “page” them?

 

[XLunacy]

Do we need to collect 5000 signatures to get a sticky, or what? who makes the decision? Do we need to “page” them?

Here are the signatures

I tried something, let's see

 

[RickDeckardCain]

This is very cool. Any chance you could do a similar analysis of G&L's L-series preamp (Tri Tone Preamp)? My understanding is that it's another Resistance-Capacitor filter which is why it works in passive mode.