The term 'Effects Unit', often abbreviated to 'FX', covers a wide range of devices. From simple distortion pedals through to complex digital sound processors. The one common purpose is modification of a music signal in some way. Various technologies are employed, most are electronic, some are electrical & a small number are electro-mechanical.

Purely mechanical devices have been used to change the nature of a musical instrument. The obvious example is a trumpet mute. In the context of this page only those that alter electrical signals are relevant. They will be listed by type of effect, followed by the various means of implementation. Not in any particular order, associated types may be grouped together.

Electronic effects fall mainly into two categories, Analogue & digital. Some include elements of both. At one time only analogue types were available. After the introduction of digital technology at studio level it took some years for prices to start to fall. Once this happened digital effects became more popular, further driving down prices. Now they form the majority.

The falling sales of analogue models forced makers to raise prices in order to stay in business. In an ironic reversal the few left are mostly seen as top end studio items. Digital on the other hand are commonplace & increasingly cheaply made. Multiple effects are combined in order to justify a high enough price to make them worth selling at all.

This has mirrored the rapid developments in computer technology. Most are sold on the basis of versatility, programming capability etc, rather than on any real sonic merit. Few have any distinctiveness, even fewer have a 'wow' factor. So many musicians now spend good money on earlv analogues or modern replicas. A strange world in some ways.

Strange when one thinks of the research, programming & chip complexity required to imitate a simple germanium transistor circuit's distortion.

Not so strange when one realises that once programmed together with a dozen other effects, they can be churned out for very little. Often by underpaid youngsters in one of the world's very many sweatshops.

On the other hand there are still a few very good digital effects. Generally expensive & mostly still intended for studio use.

A phaser works by mixing two signals of equal amplitude. One is an original signal, the other is a version of that signal shifted in phase. In a practical electronic device the shift is created by a battery of series capacitor/ parallel resistor stages, commonly four, each buffered by an amplifier. Negative feedback maintains unity gain for each stage.

Below a certain frequency each stage begins to advance the phase of a signal. This shift increases as frequency is lowered, eventually approaching 90 degrees. Thus four stages can produce a shift approaching 360 degrees, an angle never quite reached.

At high frequencies where little shift occurs the shifted & original signals add. At low frequencies, where shift is near to 90 degrees per stage, the signals also add. At one frequency only, shift is 45 degrees per stage, 180 degrees overall. At that one frequency the signals cancel exactly, giving no output.

Cancellation (minima) occurs at only one exact frequency, but addition (maxima) happens over a wide range of frequencies, to a greater or lesser extent. A graph of the response shows two broad maxima separated by one very sharp, narrow minima.

If a large number of stages are employed a number of narrow minima, one for every 4 stages, separated by broad maxima, will be produced. With phase shift the minima are equally spaced & the response resembles a comb. It is thus often termed a 'comb filter'.

Using a large number of stages is not a practical proposition, for several reasons, one of which is cost. However there is a way of obtaining similiar results simply & at low cost. As the overall gain remains at unity the shifted output can be fed back to the array input with no danger of feedback oscillation.

This signal is shifted further on its next pass & then fed round the loop again. In a practical circuit the proportion of output fed back can be adjusted, fron zero to 100%. When set slightly below maximum the signal loops a number of times before being attenuated to inaudibility.

This creates the classic comb filter response. If the resistor values of each stage are changed together, the minima frequencies change. Moving the teeth of the 'comb' through the audio spectrum. If this movement is slow & cyclic it results in the sound usually associated with phasing. White noise as a source can sound like waves on a beach.

If the cyclic change is faster, around 7 C/S for example, with feedback reduced, the result is more like vibrato, with music signals. In this case the original signal can be disconnected, for a clearer effect. A similiar technique has been used for rotary speaker simulators, realism is not that good but it has served a purpose for years.

There are number of alternative ways to adjust several resistors together. A common one is to use the channel of a field effect transistor (FET) as each resistor. With all gates connected to a common variable bias. This bias can be from an oscillator, a potentiometer, or both.

A problem with most phasers is a fairly high noise level. From the ICs used as amplifiers & often from the FETs. Another reason to keep the the number of stages down. Spending more on better components helps here, as does using light dependent resistors.

Take a 'ladder network' of six series capacitors & six shunt resistors. Set the values of each pair for a phase advance of 60 degrees @ 1 cycle per second. This gives a total phase advance of 360 degrees, one full cycle, which is one second. Thus, it seems the output signal for each part of each cycle appears at the output, one second before the input Voltage that causes it.

An oscilloscope trace will confirm this. The implication is that each Voltage change arrives before it starts. In theory such a network can be extended almost without limit, provided amplifier stages are added to make up circuit losses. How far can the time advance be pushed & is this time travel? It is certainly a provable & measurable effect of a very simple circuit.

The answer will be placed on the 'Capacitors' page.

A flanger works uses a similiar principle to a phaser. The main difference is the use of a time delay insted of a phase shift. The delay is mixed in equal proportions with the original signal as before.

This creates maxima & minima in a similiar way. These are however, spaced by an equal frequency percentage, rather than equal frequency amount. The sonic result is different..

A 'musical' ringing effect is produced, especially with feedback. Similiar to the effect of a pipe or closely spaced walls. This type of sound sometimes interferes with music, especially with certain types of chord structire. It should be used with care.

The delay is normally obtained by a digital delay line & is shorter than that required for reverberation or echo. Previously such techology was too expensive for general use oitside studios. Charge coupled delay or 'bucket brigade' circuitry filled a need for stage use.

The term 'Flanging' comes from the original way the effect was achieved, before electronic versions became available. Two identical tapes were loaded on a pair of precision tape decks. Both were set to a start point and played back in exact step.

Gently touching the feed spool flange on one recorder caused it to drop behind by a small amount. Another touch would increase the delay. Touching the flange on the other machine caused it to drop back into step.

Naturally such a procedure was only practicable in a studio, using expensive equipment. The advent of electronics opened up both phasing & flanging to a wider customer base. However both are now out of fashion, probably having been worked to death by overuse.

Spin Doctor

The first of a series of electro-mechanical signal modifiers has successfully survived a year long reliability test. This technology belongs to the future, with considerable evolutionary potential, & can give traditional digital electronics a run for its money in many applications.

This first gives Vibrato, Chorus, Tremulant & Phasing. In true stereo & unlike those from electronic alternatives. The absence of electronics within the device allows low distortion & noise. Potential uses include pre vibrato Hammond organs, electric pianos & guitars.

Spatial Vibrato is especially interesting, also working with Tremulant, Chorus & Phasing. A rotating sound pattern spreads across the stereo field with constant animation. It is complex, cyclic & effective at all speeds.

The nearest analogy is the Doppler shift & reflections of a rotary speaker. It is however unique & with good speakers delivers an even frequency response plus greater brilliance.

Its primary structure is our non-electronic analogue of an acoustic space, an Orbiter projects music signals around this space. These are collected at suitable nodes for amplification.
A twin orbiter version will be able to accelerate or brake at different rates for bass & treble.

Building of the production model will start when current restorations are complete.
Selecting here will show more information.