buildafriend

Generating Upper and Lower Harmonics
« on: December 16, 2018, 09:21:32 PM »
hey all,

we know that certain circuit topologies and pieces of equipment have more or less harmonics. that said, what circuit blocks are cool for generating more upper and lower harmonics intentionally and not just as an artifact of the circuit at hand? I'm looking for less obvious things than just eq boost the fundamental or use a tube circuit and something more like a circuit that is made to do this specifically without adding much odd order distortion

cheers,


alexc

Re: Generating Upper and Lower Harmonics
« Reply #1 on: December 16, 2018, 09:36:10 PM »
Adding harmonic distortion  is the process ....  sometimes called 'exciters' or 'enhancers'   have been out there for a long time.

They give some control over the amount and type of 'harmonics' added  ..  to some degree you can control the 'lower' harmonics ('girth' and such kinds of names) and the 'upper' harmonics  ('sparkle'  etc).

They do operate to some degree as equalizers, but *not* as straight-forward ..   as in 'typical boost/cut around a centre freq';  some have filters with some observance of the  'fletcher'munson' phenomenon in the curves.

Then there are the more subtle types, that do 'dithering' and  'pre-emphasis' types of processes  ...  that add certain distortions as part of an encode-decode operation.

And of course, the whole range of clippers and distortion units of many kinds  ...  one can parallel mix a certain amount of (bandlimited and eq'd) distortion sources with the programme material  ...  to various effect.

For predominantly h2 distortion, imho, nothing beats a really good tube in a simple gain stage, set up for clean.

You can also get there with simple class-a transistor/fet type circuits too. JLH and Neve and so on ...

..

I have an old 'spl vitalizer'  which adds hi or low harmonic distortions in a fletcher-munson approach   ...  it's not what I would call transparent!  The 'stereo width' part  also adds a good dollop of distortion.
« Last Edit: December 18, 2018, 12:34:41 AM by alexc »
I ping therefore I am

buildafriend

Re: Generating Upper and Lower Harmonics
« Reply #2 on: December 16, 2018, 10:14:01 PM »
thank you so much for your reply alexc. I'm specifically wondering what circuit blocks exist just to generate upper and or lower harmonics and how do they work? what do the schematics look like?

cheers,

scott2000

Re: Generating Upper and Lower Harmonics
« Reply #3 on: December 16, 2018, 10:42:19 PM »
Maybe some kind of null after the process of adding/creating harmonics???

« Last Edit: December 16, 2018, 10:46:37 PM by scott2000 »

JohnRoberts

Re: Generating Upper and Lower Harmonics
« Reply #4 on: December 16, 2018, 10:59:38 PM »
Harmonic distortion (is distortion)... All circuitry when distorting a sine wave, generates distortion products that are multiples (higher) of that fundamental sine wave frequency.

Distortion from playing multiple tones can generate interference tones higher and/or lower than the stimulus frequencies (difference frequencies).

I spent my career trying to avoid distorting signal paths.

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...

buildafriend

Re: Generating Upper and Lower Harmonics
« Reply #5 on: December 16, 2018, 11:53:24 PM »
Thank you John for taking the time to reply. Certainly signal integrety and distortion can be important considerations, as can odd order and even order harmonics if they are unwanted at the time. There are EE college courses on the subject of avoiding distortion - which can be a very broad term.

Enhancing harmonics is often desirable and often not. Right now my interest is in enhancing them :)

rackmonkey

Re: Generating Upper and Lower Harmonics
« Reply #6 on: December 16, 2018, 11:58:43 PM »
Pete Millett did a presentation on "the sound of distortion" at a conference and used the attached deck in the talk. He has a schematic at the end of the presentation for a device to generate different orders of harmonics, e.g., predominantly even, predominantly odd, higher order, etc. Probably doesn't do exactly what you're looking to do, but the circuit is starting point. He happened to use tubes. I know you mentioned something about not using tubes, but if you're opposed to it you might be able to learn from it either way.

This thing seems to do what I imagine the Thermionic Culture Culture Vulture does.  But this is more a science experiment than studio toy.  I keep meaning to build it, but never seem to get around to it.

BT
Whether you think you can or you think you can't, you're probably right.

scott2000

Re: Generating Upper and Lower Harmonics
« Reply #7 on: December 17, 2018, 02:31:26 AM »
Some pretty good info in this.......

http://www.tubebooks.org/Books/bbc_feedback.pdf

ruffrecords

Re: Generating Upper and Lower Harmonics
« Reply #8 on: December 17, 2018, 02:42:12 AM »
Harmonics are generated by non-linearity in a circuit. In most circuits the biggest non-linearity exists in the active devices - tubes and transistors. The topology of the circuit can also affect the spectrum of the distortion.

So, for example, single ended class A triode circuits tend to generate mostly second harmonic distortion, single ended class A pentode and semiconductor stages tend to generate mostly third harmonic distortion and in terms of topology, all push pull circuits tend to cancel even harmonic distortion.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

abbey road d enfer

Re: Generating Upper and Lower Harmonics
« Reply #9 on: December 17, 2018, 03:07:24 AM »
like a circuit that is made to do this specifically without adding much odd order distortion
This definitely calls for digital processing. That's what harmonizers do; the transposition range of commercially available ones may be limited, but a good DSP designer can do exactly what you wish.
No one has found a way to create a circuit based on non-linearities to generate precisely selected harmonics. It's mathematically impossible.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


Re: Generating Upper and Lower Harmonics
« Reply #10 on: December 17, 2018, 05:31:24 AM »
I'm looking for less obvious things than just eq boost the fundamental or use a tube circuit and something more like a circuit that is made to do this specifically without adding much odd order distortion
Presumably one could design a fundamental-tracking filter and use it to control a bandpass filter that will then track (and e.g. boost) a chosen harmonic, without adding any new harmonics... It would only work for fairly simple waveforms though, where the fundamental is easy to identify and lock-on to.

Another option I suppose would be to use a pitch shifter to create, in effect, any desired harmonic, and mix it back into the dry sound.
« Last Edit: December 17, 2018, 05:37:27 AM by merlin »

Script

Re: Generating Upper and Lower Harmonics
« Reply #11 on: December 17, 2018, 06:15:05 AM »
The Vitalizer uses an LC filter to add
high 'harmonics'.

The bass, IIRC, is a notch filter followed by a positive feedback opamp, I think. But there might be more to it than that.  Followed in later versions by a compressor to tame the signal.

In best ad language, the manual explains it all more in terms of 'pushing part of the signal forward in time' -- probably as opposed to adding diode distortion underneath  as Aphex units do.

abbey road d enfer

Re: Generating Upper and Lower Harmonics
« Reply #12 on: December 17, 2018, 06:38:03 AM »
The Vitalizer uses an LC filter to add
high 'harmonics'.

The bass, IIRC, is a notch filter followed by a positive feedback opamp, I think. But there might be more to it than that.  Followed in later versions by a compressor to tame the signal.

In best ad language, the manual explains it all more in terms of 'pushing part of the signal forward in time' -- probably as opposed to adding diode distortion underneath  as Aphex units do.
Indeed, a basic EQ can be used to enhance already existing harmonics, but for creating harmonics from an incoming signal takes some form of distortion or pitch-shifting (it may be argued that pitch-shifting IS distortion).
Since any real-world circuitry has distortion, it is sometimes difficult to identify what part of the processing one actually hears predominantly.
The "time-forwarding" is just a consequence of high-pass filtering.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

L´Andratté

Re: Generating Upper and Lower Harmonics
« Reply #13 on: December 17, 2018, 08:08:47 AM »
From Rob Hordijk "Synthesis Workshop"
https://rhordijk.home.xs4all.nl/G2Pages/
Quote
There is a simple trick to produce even harmonic distortion that works on all synthesizers that have a linear VCA and a means of inverting a signal. The idea is to use a fixed control voltage on a VCA control input in such a way that the VCA amplification is exactly one or unity gain. Then a little bit of the input signal into the audio input of the VCA is mixed with the fixed control voltage. When the input waveform is positive the gain of the VCA will increase slightly while when the inputs signal is negative the gain will be slightly reduced. It is like the signal is compressed when negative and expanded while positive. When set this way the VCA will generate the second harmonic of each sinewave partial that is present in the input signal. The amount of distortion is set by the amount and the polarity of the signal that is added to the fixed control value for the VCA. Beware that the maximum level of the modulation signal is about half the fixed voltage or control value, exceeding this value might cause some true analog VCA’s to stop working.
Strictly amateur since 1973...

plimousse

Re: Generating Upper and Lower Harmonics
« Reply #14 on: December 17, 2018, 08:45:38 AM »
May be a track ...
« Last Edit: December 18, 2018, 03:53:04 AM by plimousse »

rackmonkey

Re: Generating Upper and Lower Harmonics
« Reply #15 on: December 17, 2018, 09:44:57 AM »
Agree about the DSP approach doing being the right path here, but I'll put this out there since others may come to this thread looking for ways to generate X or Y harmonic distortion.

Analog circuit using JFETs to generate predominantly second harmonic distortion. This may be from the Leach files, but then it may not be.  It's from Ga Tech either way. Simple circuit.

BT
Whether you think you can or you think you can't, you're probably right.

abbey road d enfer

Re: Generating Upper and Lower Harmonics
« Reply #16 on: December 17, 2018, 09:49:32 AM »
May be a track ...
Your link is 404 to me...
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

abbey road d enfer

Re: Generating Upper and Lower Harmonics
« Reply #17 on: December 17, 2018, 09:52:28 AM »
From Rob Hordijk "Synthesis Workshop"
This works for synths because the level of the oscillators is stable, so the substraction works well. When the level is variable, the squared signal's amplitude varies in a different ratio to the original signal, so the tonal result changes significantly.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

abbey road d enfer

Re: Generating Upper and Lower Harmonics
« Reply #18 on: December 17, 2018, 09:55:05 AM »
Agree about the DSP approach doing being the right path here, but I'll put this out there since others may come to this thread looking for ways to generate X or Y harmonic distortion.

Analog circuit using JFETs to generate predominantly second harmonic distortion. This may be from the Leach files, but then it may not be.  It's from Ga Tech either way. Simple circuit.

BT
Their math just shows that the amount of 2nd-order is directly related to the square of the signal, which results in significant tonal change in respect to amplitude.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

scott2000

Re: Generating Upper and Lower Harmonics
« Reply #19 on: December 17, 2018, 09:58:10 AM »
I'm having issues with my image attachments but I wanted to ask what kind/types of harmonics/distortion are present across a push pull stage biasing resistor as it relates to monitoring this point for balancing????

edit//// let me try this again....
« Last Edit: December 17, 2018, 10:12:11 AM by scott2000 »


 

Related Topics

  Subject / Started by Replies Last post
2 Replies
1060 Views
Last post September 21, 2005, 09:33:52 PM
by rodabod
4 Replies
1198 Views
Last post March 06, 2012, 10:30:00 AM
by inputhone
63 Replies
14835 Views
Last post February 01, 2014, 11:45:02 AM
by kato
7 Replies
2503 Views
Last post June 28, 2013, 11:40:58 AM
by Paul678