[skm]

In the spirit of Lou's articles on Q&A I've decided to start the ball rolling in Effects with a primer. This is going to start off with laymans descriptions so everyone is on the same footing, then I'll go into how the effects work and the electronics (for building and customisation). I'll do a post every time I get bored at work... expect a complete tutorial in no time at all!!!

(Mod Edit......... Since Skm has included a lot of info in this topic I think making it sticky is a good idea. HMB)

Amplitude based effects
This means effects that work on the sound level of the signal. The simplest example is a volume control. I'll start with a list of the basic effects in this category, then I'll say a little about them.

Volume Control
Tremolo
Compression
Swell

Volume
Speaks for itself really. Turn it up, your volume increases and vice versa.

Tremolo
Due to the 'tremolo' on a guitar varying the pitch, this is often taken as a pitch varying effect. A true tremolo "wobbles" the volume up and down. This can be taken to extremes with an effect called gating which cuts the signal from off to full volume at regular intervals. As the sound is decaying this makes it sound like a repeating note getting progressively quieter.
Another variation on tremolo is panning or ping-pong (named after a recording technique). This sends the output of the tremolo to different channels and increases the volume in one channel as the other decreases, giving the effect of the sound bouncing between the two speakers.

Compression
This effect makes loud sounds quieter and quiet sounds louder, lessening the dynamics of what you play. Included in this category is the opposite effect - Expansion - which makes quiet sounds quieter and loud sounds louder. These are often used in conjunction for noise reduction in studios. There's also limiting. This only reduces the volume of a signal past a set threshold level. Anything under the threshold is left unprocessed. These compression effects can cause 'clipping' of the louder sounds, which is essentially the top of the signal being chopped off. I'll come back to clipping when I talk about distortion effects.

Swell
Swell takes a note and progressively changes the volume, usually from low volume to high volume to imitate the effect of a bowed instrument or wind instrument.

[skm]

Distortion Effects
As has been mentioned in other posts, there is no real technical difference between Overdrive, Distortion or Fuzz. They are variants of the same effect with no hard definitions. Usually the milder the effect the more chance it has of being called overdrive, working it's way up through distortion and on to fuzz. This post will describe different ways of getting this distortion.

Clipping
Here's where a little physics comes in handy. A basic note can be thought of as a sine wave, which is little more than the most basic of all wiggly lines.

Clipping is nothing more than flattening the tops and bottoms of the peaks. What does this do to your sound? Well, a sine wave is the most simple wave. Any other wave can be made out of lots of different sine waves (called harmonics). When you flatten the wave, it's just like adding hundreds of new waves together to make the flattened wave. This gives you a richer sound and is the effect we call distortion.
It's also called overdrive. This is down to the way it occurs naturally in circuits. If the signal is too big for the circuit to cope with, it clips the signal, ie. you're driving the circuit too hard - the circuit is being 'overdriven'. It's just different terminology for the same thing.

Clipping from tube circuits (rather than transistor-based circuits) has a slightly different sound as the clipping isn't symmetric. From a tranny circuit you'll get the same clipping on the top and bottom of the waveform, a tube circuit will generally clip the top more than the bottom. This asymmetry gives the higher squeal of tube distortion as well as the slightly more 'organic' sound.

Next post: Distortion continued... (including fuzz and octave effects).

[ratm50]

this is a pretty cool idea I'm sure that it will help lots of people out. I mean, we have threads all the time wanting to know what pedals do or what they are, for example tremolo and fuzz are some of the most recent posts.

[halfmoonbay]

Nice one. It'd be nice to see some stuff on pedal construction/mods.

[skm]

Distortion effects continued...

The hardness or softness of the clipping matters. Hard clipping happens when the output wave equals the input at a given level, then stays at the clipping level until the input drops below the threshold again, as described above. Soft clipping has no abrupt clipping level, but gently compresses the peaks of the signal so the waveform is still slightly rounded. Soft clipping emphasizes the 'lower-order harmonics', meaning waves closer in shape to the original, thus giving a more natural sounding distortion. Hard clipping has a mix slewed to the 'higher-order' harmonics, which are harsher sounding (and those more commonly heard in metal-style distortions and fuzz pedals).

The next step after clipping, which you can think of as squaring the wave off, is to amplify the wave massively first so that when it clips it's practically square. This extreme version, called infinite limiting gives a very harsh and buzzy distortion. It's seen mostly in fuzz pedals.

What happens when you take asymmetric clipping to the extreme? You end up with half the wave clipped flat (say the bottom half) and the other (top) half completely unchanged. This is called half-wave rectification. In terms of the other waves you have to add to get this wave, the strongest is the 'second harmonic', which produces an octave effect (original signal + one octave up). If we take the final step and rather than clip the bottom half of the wave flat we actually invert it so we just have a series of bumps (full-wave rectification). This has a very strong octave effect, but also introduces a slew of distortions.



The final part of distorting waveforms is artificial generation (aka synthesizing). This effect generates a completely new waveform at the same frequency (note) as the input. On it's own, the shape of the waveform can be set to emulate different instruments, a la guitar synth, but a wave can be generated at the same note (or an octave or two apart) and mixed with it. A whole variety of effects can be made this way.

Next: Umm... I haven't decided. Probably frequency altering effects, but you never know.

[ratm50]

definately cool, good job man.

[thumz]

Yep, very interesting. Can you tell me what a phaser is? And Flanger?

[ratm50]

I will leave the honor for you to post skm.

[skm]

Phasing and Flanging
Phasers and Flangers have similar effects which can be thought of in two very different ways.

Flanging was originally a studio effect applied very roughly by the engineer. It was done by playing two reels (tapes) of the guitar track simultaneously and then slightly slowing one down by dragging a finger across the reel. On release the reel would speed back up (and the engineer might speed it up slightly to catch back up with the other tape). In this sense flange is a time-delay effect. The signals from slightly different parts of the tape are mixing together. However the amount of drag applied is only slight, but when the tape is slowed down the pitch of everything played back drops. The ultimate effect of this studio trickery is to have the original sound mixed with a varying-frequency copy of the original. The addition of the waves causes certain frequencies to be enhanced and others to be cancelled. The frequencies affected change as the tape speeds up and slows down - this gives a frequency 'envelope' that swooshes up and down. If the effect is applied for longer, you get a longer swooshing effect - if the effect is applied (subtley) for a very, very short time, a chorussy effect can be achieved.

Phasing is a frequency-based effect. If two guitar strings are vibrating at the same frequency (note), and are vibrating precisely together (ie. each going up and down at the same time) then the vibrations are 'in phase'. If the strings don't vibrate in precisely the same way they are 'out of phase'. When you add up the waves produced by both strings you get bits where they add together and bits where they subtract. Hence you get bits missing from the wave (called 'notches'). What does this do to the sound though?

Well, it's a very limited way of mimicing a flanger. Hence a characteristic 'swirly' sound.

[mrwobbles]

If i could add just a 'little something' about placement of effects... :smile:

Probably the main thing to understand about effects order is that an effect modifies the sound it receives. This means if you plug your guitar into a fuzz box, the fuzz box gives you a fuzzy guitar sound - pretty obvious, huh? If you then plug the fuzz output into a wah pedal input, then the wah works on the fuzz sound, giving you a synth-like wah sound.

If you plug first into the wah, then into the fuzz, it gives a completely different sound. That's because the fuzz is working on a guitar sound that already has a wah effect. You may know that distortion effects like fuzz have more effect on loud sounds than quiet ones (that's why they sound cleaner when you roll off the guitar volume). And a wah pedal makes different notes and frequencies louder and softer as you rock the pedal, so rocking the pedal also now controls the amount of fuzz as well, giving what most players prefer as a more interesting effect.

There are no rules on effects order. You won't break any pedals by putting them in a 'wrong' order. In fact, experimenting is the best way to learn, and in doing so, you can come up with many unusual and interesting sounds. There is, however, a typical order of effects that I've listed below.

Before we get into the order, though, you might like to consider why, when & how you use effects. My most deep piece of wisdom to pass on is that the subtle use of effects is suitable for long periods of use, while intense effects have most impact when used briefly.

For example, light phasing or chorus can be used for an entire song, adding some texture to backing rhythm. Dramatic effects like strong delay, wah, or even playing techniques such as continuous fast picking without a rest, become tiresome when overused.

Typical Order
A good starting order, from guitar to amplifier, is:

Filter effects
Phaser
Wah pedal
These effects sweep a peak (wah) or notches (phaser) in the frequency response. By placing these before distortion effects, they vary the distortion intensity of the affected frequencies at the same time.
The original Vox and Cry-Baby wah pedals did not use a true bypass when off, and can load your guitar signal. If this is a problem for you, you might want to have the switch replaced with a true bypass.

Another way around the problem is to use a "buffer preamp" before the wah, which can be any effect with electronic switching, turned off. If you use a phaser as well, plug that in first, and it will happily drive the wah pedal.


Compressor
Even though many players suggest compression should be first, there is benefit in placing it after filter effects. Filter effects can reduce volume at some settings (eg heel down on the wah pedal, notches in the middle frequencies from a phaser, etc), so placing a compressor after these effects can even out volume changes.

Overdrive/Distortion
Stomp-box effects
or your pre-amplifier drive channels
Placing overdrive after the filters gives them a more natural sound, like placing your wah pedal before a heavily overdriven amplifier. Using the filter effects after overdrive gives them a much stronger, more synth-like sound.
You would not normally need to use heavy compression and heavy overdrive together.

There can be merit in using light EQ before the overdrives (used only when the overdrive is on); this gives you the ability to change the character of overdrive. For example, boosting the highs before overdrive, but cutting highs after overdrive (with the overdrive's tone control), will balance the highs overall, but cause them to be more heavily overdriven than the lower strings.

The overdrive could be the preamplifier in you amp. You can use this if your amplifier has an effects send and return, to allow you to use the remaining effects below. You may need to check the levels sent and expected by the send/return loop; often they are designed for line level only (eg rack equipment) and not the lower level stomp boxes.

Some send/return loops allow you to blend the return in an equal mix with the unaffected signal. This is great for not affecting your original signal, which can become quite unnatural if taken from the amp, processed by one or more analog-to-digital-to-analog conversions, then re-input. This increases the complexity though, when you want to remix chorus, flange, delay and reverb, all without any original component. Also, you may want some of these effects to be fed with inputs of a mix of original and other effects. These capabilities are often not provided in rack products.


Equalisers
Graphic
Parametric
Speaker Simulators
These effects can be used on their own, to tailor solo or rhythm sounds, or with overdrives to give more control than you usually have with the overdrive tone control. For example, you could use heavy distortion, and use equalisation here to cut middle for a heavy sound, or tailor the highs for a creamy, yet "bitey" Santana sound, etc.

Speaker simulators are mostly preset, and highly tailored equalisers to emulate speaker box resonances, and microphone techniques. Some include other subtle effects, such as short delays, as well. Placement is not as crucial as you might think. For example, most recorded sounds use a microphone in front of a speaker box, then studio effects, such as equalisation, chorus, delay, etc applied afterwards.

On the other hand, when you play live, and are using a variety of effects through a stage power amp and speaker box, you might want to use the simulator here only for the purpose of feeding the mixing desk (who apply their own delay and reverb for the front mix). You could bypass the simulator on stage, and apply just enough delay/reverb to give a natural on-stage sound.


Pitch Effects
Harmoniser
Vibrato
Pitch benders
Harmonisers in particular should be placed after overdrive. In the opposite order, sending several notes to the overdrive input causes strong inter-modulation distortion where additional, usually low, notes are added. These extra notes may have no relationship to the harmony you intend.

Modulation effects
Flanger
Chorus
These are effectively combined filter, delay and pitch effects. Because each of these effects is subtle (unless you set high resonance), many players prefer them after distortion, and prior to echo effects.

Level controllers
Noise gate
Limiter
Volume pedal
Tremolo
Panning
Placing level effects before echo effects allows a natural echo sound. For example if you play a loud chord, but fade it out quickly with a volume pedal, you still want to hear the echo on what you played. The other way round, with echo first then a volume pedal, you would hear a loud chord with echo briefly, with both the main souund and the echo quickly cut out to silence. This sounds about as natural as turning the power off on your amp!

Echo Effects
Delay
Reverb
These effects are usually placed last to allow you to emulate the effect of using an amplifier in a "lively" room.

[reprisal]

nice stuff... stuff i never knew

[skm]

Look at that... I go away for the weekend and already someone is trying to usurp my position!!!

Thanks for that Mr. Wobbles. It saves me a post...

I do have to sit and think about what to do next though. I'll be back when I have a clue.

[skm]

This is partly a post just to bump the topic to the top, but so's it's not just aimlessly increasing my post count I'll do a little about reverb.

Reverb
Natural reverb (short for reverberation) comes from playing in an "acoustically active" room, ie. one with lots of hard surfaces for the sound to bounce off. Step under an underpass and shout something... the echo you get here is reverb. In most amp combos that have a reverb capability this is done with a 'spring reverb'. This is quite literally a couple of leaf springs in a box.

(Though I found this home project where someone made a reverb with a slinky!! http://www.angelfire...gs/springs.html)
The signal from the guitar is transformed into a vibration on the spring (like happens at your speaker) using a transducer and the signal (now affected by the responses of the springs) is picked up by anther transducer at the other end of the spring. This is the normal mechanical way of producing the sound of playing in a concert hall (or for a shorter reverb, a studio). There are plenty of digital reverbs to do the same job now, but these can be expensive and I don't really know how these work at the moment (I have my suspicions, but I'm not sharing in case I look foolish and undermine my credibility!)

More soon...

[skm]

Pedal Construction
Pedal design is a difficult subject, and one that needs a good understanding of electronics. So I'm not going to discuss it, it'd take far too long. If you're interested, I suggest getting a book on linear electronics and studying. What's left to talk about then?

Building pedals from schematics.

Circuit diagrams are available for many famous pedals, whether drawn by enthusiasts or the manufacturers. Usually they're pretty easy to follow with a basic level of knowledge. Here are some of the usual components you'll find.

Resistor:

(Often also drawn as a zig-zag line)
Dissipates energy. This is a very important component in all circuits. The current in a circuit is related to the voltage and resistance by Ohm's Law, Voltage = Current * Resistance. For a constant voltage, a change in resistance will change the current flowing.

Capacitor:

Stores electric charge (like a battery). During charging, the voltage across a capacitor increases with time; used when a time delay is needed.

Resistors (and occasionally capacitors) have an arrow either through them or pointing at them. This means they are a variable component.

Diode:

The diode only allows current to flow one way across it.

Transistor:

(Also often drawn inside a circle).
The letters mean Base, Collecter and Emitter. Transistors act as a switch in the circuit.

Op-amps:

Operational Amplifier. Amplifies the input voltage. Has a very high resistance so current flow is low. The op-amp has two inputs (inverting and non-inverting) and one output. A resistor placed between the output and the inverting input provides feedback and allows adjustment of the level of amplification. These have many different functions in a circuit.

ICs:
Integrated circuits. These are basically microchips. The standard is an 8-pin chip. ICs can have almost any purpose, since they are a whole circuit, miniaturised on a silicon (or germanium) wafer. They can be an amplifier, oscillator, timer, counter, computer memory, microprocessor or more.

I'll add to this with time and explain the methods of putting circuits together; the pitfalls in home effects-building; why you lose tone in circuits (and how to avoid it); and how to modify effects.

[desertninja]

i get a really annoying humming sound, almost like a bad ground wire, when i have my pro co rat, and my big muff in the same pedalboard setup (my board changes constantly) is there a way to get rid of this noise? i saw a pedal that is supposed to fix this problem but i have not had a chance to check it out.

[ratm50]

Yep, there is the boss noise suppressor and noise gate. Then there is the mxr noise gate(think that's it's name) and a few other companies make noise gates but you get the picture, just search for noise gates.

[halfmoonbay]

It sounds like you may have some sort of earth loop or something, they cause a constant hum........ I had a problem with that kind of thing just recently, I fiddled around with my cables/leads and it sorted itself out. Also, sometimes having the audio leads near a power supply or power cables can cause a hum, especially if you have coils of audio cable lying around. And then of course there's static, but that'd be creating more of a crackly noise than a constant hum.

[folkgirl]

Wow Dr. Steve, this is very interesting indeed! you sure do know your stuff. I like all these graphs and diagrams and stuff. I find things easier to understand if there's a visual supplement as well.

I'm the lowest of all FX begginers, i don't even have an electric guitar but this is all very fascinating nevertheless :grin:

[skm]

Ibanez TS-9 Tubescreamers:
The infamous "808" mod.

Since people have been talking about this one, I did some digging and I've found some mods. I take no credit for these. Just for my beautifully clear prose.

It seems to be a very basic modification... the diagram shown should help. Find the resistors labelled Rb and Rc, the series and shunt resistors respectively.
On the TS-9 these are the 470 ohm and 100k ohm resistors. You'll find them on the output buffer transistor, so trace back from the output jack to find them, and replace them with a 100 ohm and a 10K ohm. If all has gone well, your pedal should now be an 808!



To do much more to your pedal you'll need a circuit diagram to help you identify the parts, and some knowledge of which bits do what.

Some components are pretty easy to identify though... most notably diodes, transistors and op-amps. These are best identified by their part numbers (which are printed on them!).

Now, cast your mind back to the distortion section. I talked about symmetric and asymmetric clipping. Don't remember? Go read it then come back.

Happy? Good. The TS-9 uses a pair of matched silicon diodes to clip the waveform. The corners are then rounded using a small (51 picofarad) capacitor. Since we already talked about the difference between the "higher squeal of tube distortion as well as the slightly more 'organic' sound" (from asymmetric clipping) let's swap to asymmetric clipping.
If you change one of the diodes then they won't clip at the same voltage. That'll give you a less "electronic" sounding distortion.

If this takes your fancy, try swapping one for a 1N4004 diode or putting another diode (eg. a 1N34A) in series with one of the original silicon diodes to add a bit more threshold voltage to one side.

There's ways of adding more distortion and changing the frequency response too... I can explain those if people are interested in modding their TS-9s.

NOTE: Diodes only let current pass one way. Do not put them in the wrong way round. One end is marked with a coloured band... make a note of which end this band needs to be when you're replacing diodes.

[guitargirlca]

niiiiiice SKM!