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SECTION 3: THE LIVE ELECTRIC GUITAR REPRODUCTION AND AMPLIFICATION SYSTEM

 



 Note: Links are shown in blue text and underlined – select and click to open

 

WHY IS IT A “SYSTEM”?

Electronically reproducing sound produced or created by a guitar requires a system, comprising a series of discrete processes connected together in sequential or serial cascade – i.e. the output from each stage in the process is the input to the next stage in the process.

 

What we actually hear is the end of the process – i.e. acoustic sound waves generated by the loudspeaker. Everything else in between is irrelevant to our ears because it is in electronic (electrical energy) form that we cannot hear.

 

So it is important to understand what the system is and how it works.

 

 

SYSTEM STAGE 1: THE ELECTRIC GUITAR

 

The electric guitar was invented nearly a century ago and has been constantly evolving as the most popular musical instrument in the world.

 

A comprehensive description of the instrument is at https://en.wikipedia.org/wiki/Electric_guitar

 

Guitar History:      https://www.youtube.com/watch?v=AjK4GVR1EcE

 

For the purpose of explaining the evolution of the modern guitar see the history of Martin Guitars, the oldest manufacturer in the USA.

 

Part 1          https://www.youtube.com/watch?v=Jv8WrYAMyvo

Part 2:         https://www.youtube.com/watch?v=x2SSiZCM1LQ

 

The guitar is an extension of the player’s mind and body and becomes a part of the player as his/her means of musical expression.

 

Consequently the choice of instrument is extremely personal and must be made with great care – unless you want to try as many different versions of the instrument as you can before settling on your instrument of choice.

 

Differences between instruments are many and varied so it is wise to explore and research before committing to purchase.

 

The “sound” of an electric guitar is just one of the essential attributes.

 

Factors such as body and neck timber species and characteristics, hollow body, semi-hollow body, solid body, shape of body, size, weight, balance, neck length, neck straightness and absence of warp or twist, number of frets, fretboard width, string height above the pickups and neck, number of pickups, type/construction of pickups, positioning of pickups, on-board controls, position of output phono socket etc. are all important.

Acoustic Tone Woods:   https://www.youtube.com/watch?v=PbeLvgzW1ow

Acoustic Body Shapes:   https://www.youtube.com/watch?v=aV7A1bqamnM

One of the most important factors is the colour and finish.

 

 

ELECTRIC GUITAR MANUFACTURE

 

Martin USA Factory Tour                  https://www.youtube.com/watch?v=WES8A918wQc

 

Fender USA Factory Tour                 https://www.youtube.com/watch?v=wbdodxel3jw

 

Fender Custom Shop Factory Tour    https://www.youtube.com/watch?v=odH_lc1QtTo

 

Gibson USA Factory Tour                 https://www.youtube.com/watch?v=1zXJtkDstH0

 

 

A good quality guitar will sound alive and vibrant -  natural resonance adds colour and depth to the sound and aids sustain. The sound should be pleasant and melodic. The sound should not be harsh – unless you prefer it that way.

 

The natural volume should be even across the neck and chords should have the same tone across the arrange of notes.

 

To set the stage, the My Twangy Guitar website provides examples of around 225 different electric guitar sounds from a range of guitars that includes solid body, semi-hollow body and hollow-body designs in different makes and models.

 

 

THE PLAYING METHOD

 

To coincide with the style of music being performed, the guitar may be played with the fingers, finger-nails, thumb, finger picks, thumb pick, a pick or a plectrum, or a slide (steel guitar and Hawaiian guitar) – and even drumsticks. (6 min 17 secs in)

 

The dynamic range of the sound produced responds to the amplitude of the string vibration, so the harder the string is plucked the louder the sound and the higher the voltage output produced by the pickup.

 

This is reflected in the playing style, which can range from be delicate, light, moderate, medium, heavy, extra heavy and aggressive.

 

Pick or Plectrum – what is the difference ?            https://www.guitarsite.com/plectrum/

 

 

 

SYSTEM STAGE 2: STRINGS

 

Acoustic Guitar Strings can be gut, nylon or steel.

 

Gut strings: https://www.youtube.com/watch?v=ZbTTKMq5sno and https://www.youtube.com/watch?v=kjVU-SRBMHA

 

Nylon strings: https://www.youtube.com/watch?v=2IYlYZ5e5O4 and https://www.youtube.com/watch?v=JL4w3ixUDdw

 

Steel strings: https://www.youtube.com/watch?v=5jSfnG8oOJI and https://www.youtube.com/watch?v=pAHGQkeQfO0

 

Electric guitar strings can be steel or stainless steel and come in various gauges, namely light, medium and heavy.

 

Electric guitar steel or stainless steel strings may be round or flat-wound.

 

Electric guitar steel or stainless steel strings may be nylon wrapped or nylon dipped.

 

The number of strings may be four or five for bass guitar, or six, seven, eight or twelve for acoustic, lead or rhythm guitar.

 

Strings are normally tuned to Concert Pitch – A440, but sometimes guitarists will raise or lower the pitch for special effect.

 

Strings should be grounded to the on-board electronics negative terminal.

 

 

SYSTEM STAGE 3: THE GUITAR PICKUP

 

The first step is the pickup(s) located on or in the guitar.

 

The pickup device is usually an electro-magnetic device.

 

For a more natural sound a piezo pickup or even a standard microphone may be used - see Chet Atkins Medley

 

The pickup generates an alternating current voltage that is supplied to the amplifier or preamplifier via a flexible shielded cable.

 

Many guitars provide more than one pickup to enable the sound tone to be varied. In such cases selector switches and a simple mixing/blending circuit are provided on-board the guitar.

Switching enables series or parallel connection of pickups.

 

Usually a simple single knob tone control is installed, providing a treble cut effect.

 

More exotic designs include a battery powered solid state preamplifier, called an “active” pickup.

 

Most commercial amplifiers provide inputs for normal and active pickup feeds as standard to accommodate high or low output from the guitar or preamp.

 

Pickups are made in a wide range of designs and sound characteristics ranging from bright, clean and accurate to dirty or muddy – see https://en.wikipedia.org/wiki/Pickup_(music_technology)

 

Their position on the guitar body has a significant relationship with the output voltage and the tone. The Bridge pickup delivers a harsh bright tone whereas the Neck pickup delivers a mellow smooth sound. Other pickups may be installed in between.

 

Some pickups are mounted at right angles to the longitudinal axis of the strings whereas others are set at an oblique angle.

 

The physical distance between the pickup and strings is critical and should be adjusted for best performance.

 

A common configuration is in the popular and much copied Fender Stratocaster guitar, that offers three pickups and a selector switch to provide a choice of five tonal settings ranging from bright to mellow. 

 

Multiple pickups may be series or parallel connected.

 

One problem that plagues guitarists is extraneous hum and noise pickup from unshielded on-board electronics, including the pickup. Various pickup designs have been invented in an attempt to minimise this irritating disturbance. The “Humbucker” pickup is one form of anti-hum device.

 

Better quality guitars use metal shielding around the electronics to prevent stray hum and noise pickup. The shielding is sometimes simply a piece of aluminium foil shaped to suit the guitar body cutout and ground by direct connection to the phono socket ground terminal either by physical clamping or a wire. Shielding may be retro-fitted.

 

By definition, changing a pickup will change the sound.

 

Fender provide a guide to selecting a pickup at their Stratocaster catalogue page.

 

 

SYSTEM STAGE 4: CONNECTING CABLE

 

The cable connecting the guitar to the amplifier must be shielded and grounded to the amplifier chassis to prevent hum and noise pickup.

 

Nowadays commercially manufactured high-quality cables are readily available at affordable cost.

 

Many styles and variants of cables are offered in the musical instrument market, each supported by performance claims and various price points. Try before you buy.

 

To prevent hum pickup ensure the phono plugs have a metal shield around the cable where it terminates to the plug. (Plastic sleeved plugs are OK for speaker connectors)

 

It is preferable for the cable to be sheathed with a tapered rubber sleeve at each end to mechanically support the cable where it enters the phono plug connector sleeve. This device helps prevent the cable fracturing mid-performance.

 

Some cables are microphonic, which means they respond to unwanted impact noise. If you have such a cable replace it.

 

It is important to use densely shielded cable to prevent stray hum and noise pickup from external sources.

 

 

An alternative to using a connecting cable is a wireless connection. This system requires a small short-range wireless transmitter to be plugged into the phono socket installed in the guitar body – or a short shielded cable installed between the guitar phono socket and a small back transmitter unit.

 

This method is popular because it offers freedom to the guitarist to move around a stage while playing. But because it is wireless operated there will be some change to the tone – comparable to the sound from FM radio.

 

In both cases the receiver unit is mounted on or near the amplifier and connected to the amplifier via another shielded cable. The receiver unit requires a separate power supply.

 

 

SYSTEM STAGE 5: THE PREAMPLIFIER – STAND ALONE OR ON-BOARD BUILT INTO THE AMPLIFIER

 

The output voltage from a guitar is quite low – typically 100 to 300 millivolts.  Similar to a dynamic microphone or a vynil record player magnetic cartridge, but significantly lower than an AM/FM/DAB tuner or a CD/DVD/Blue Ray Player.

 

The core role of a preamplifier is to increase the signal voltage from the guitar to that needed to fully drive the first stage of the tube Power Amplifier section to maximum amplifier power output – usually set to between 0.7 and 1 volt.

 

That means the minimum voltage gain for a pre-amp needs to be up to ten times its input voltage – i.e. a gain of ten times. Multi-input preamps incur insertion losses in the mixing circuits so the overall gain needs to be sufficient to offset any losses.

 

Obviously the output voltage from the guitar pickup(s) will be proportional to string amplitude when picked or plucked, so a gain/volume control is necessary to cater for different pickup performances and different playing styles. The pre-amp gain control is usually set to provide maximum amplifier power when the guitar volume control is set to maximum, to allow the guitarist to adjust volume without having to touch the amplifier/preamp.

 

The second function of a preamplifier is to provide some means of varying the tone of the sound.

 

This is usually achieved by including independent bass, midrange and treble Tone Controls.

 

Bass, treble and midrange tone controls add further insertion losses and require a tube voltage amplifier stage to restore gain back to unity. Usually this means another tube stage.

 

Standard tone controls offer + or – 10 to 15db cut/boost at lowest and highest frequencies of 30 to 50Hz and 10-15kHz.

 

Some designs included a “presence” or mid boost control.

 

An alternative to an additional stage tone control pre-amplifier is the Graphic Equaliser. They come with a range of bands and boost/cut frequencies. A tube based Graphic Equaliser requires a minimum of a single triode stage to provide 10-20 db boost for each frequency – e.g. five twin triodes for a ten band unit. Consequently solid state construction is a more practical solution. Solid state EQ’s are readily available in up to 32 band options in both mono, two channel and stereo modes. Note however that Graphic Equalisers provide “pyramid” boost/cut profiles compared to the gentle slope of a standard logarithmic tone control.

 

Some designs offer shelving filter controls.

 

Some designs, such as the Behringer Ultra-Q T1951 tube EQ offer variable frequency and shelving settings for each band.

 

The Realistic 12 Band Graphic Equaliser is typical of the genre.

 

More modern models by Phonic are shown at https://www.phonic.com/images/products-II/GEQ3102F/ds-GEQ1502F-GEQ3102F-en.pdf?type=file

 

EQ Pedals are also readily available.

 

Note that PA (Voice) Class EQ’s usually have a limited frequency range to inhibit acoustic feedback in live performances. It is recommended that a full range EQ (40Hz – 16kHz) be used to ensure full harmonics are amplified. This more important if bass guitar is included in the mix.

 

Modern solid state amplifiers often included “pyramid” controls that provide a high amplitude narrow band boost or cut facility – similar to a multi-band graphic equalizer - however this is usually not practicable with tube preamps because it means more stages and more hum and noise.

 

The primary disadvantage of on-board built-in pre-amplification effects and tone controls is that the player cannot adjust them whilst playing. Pedals offer also the advantage of being able to be easily replaced to obtain a different tones or effects.

 

 

SYSTEM STAGE 6: OPTIONAL REVERB/ECHO EFFECTS

 

Reverb

 

“Reverb” was introduced in the 1960’s using a mechanical coil spring reverb unit adapted from the Hammond Organ. These were widely used for “surf” music and are still fitted to some OEM amplifiers.

One of the earliest examples is the track “Baja” by the Chantays and The Ventures and The Astronauts.

 

Other means of constructing reverb units include a light sensitive resistor (LDR) supplied from an oscillating lamp light source that varies the light amplitude.

 

Another used multiple delay stages - e.g. the Carvin Quad X hybrid solid state/tube preamp.

 

The Spring Reverb unit remains very popular in OEM amplifiers. It has a mechanical sound to it and is often characterised by a distinctive “whip” or ringing sound at the end of each note.

 

Good examples are  Bulldog and Footpatter and Tourqay and Misirlou – Pulp Fiction and Yellow Jacket

 

Spring Reverbs are very microphonic – i.e. pick up and amplify unwanted external vibrations when in close proximity to other instruments.

 

Reverb is explained further by Fender

 

 

Echo

 

Another form of echo unit is the endless loop tape echo units. This form of device uses standard ¼” tape endlessly rotating over several selectable heads. By head selection and mixed gain a wide range of delays can be achieved.

 

One early example of the technique is from Santo and Johnny in an alternative take of Sleepwalk from 1959. The playing technique is shown in this live TV recording.

 

A popular band based on this technology is the UK band ‘The Shadows”.  In this clip both the lead and rhythm guitars use echo units, then the entire band has studio echo added as well. Other examples of tape echo Shadows tracks are Apache and Sleepwalk and Blue Star and Geronimo and Man of Mystery and Wonderful Land and Going Home and Atlantis

Other generic examples of echo enhanced guitar are Cicci Guitar Condor and Dire Straights.

The Klempt Echolette was a fine example of a very functional popular tape echo unit.

 

Another intro level tube based echo unit is the “Watkins Copycat”.  Was made in the UK.

 

The tapes wear quickly so several spares may be needed to get through a full performance.

 

For practical reasons, this type of tape delay preamp is not viable to instal in the main amplifier unit so it is advisable to use a stand-alone external unit.

 

Solid state preamps offer all of this and more in a low cost compact format – but do not provide the tube sound.

 

The Carvin Quad X preamp is a hybrid solid state/tube unit that also offers various echo and reverb effects.

 

Of course studio created echo/delay is legendary, commencing very early in the 1950’s. This commentary explains the really great effect achieved on this compilation track from Gene Vincent in 1957 - Guitar by Cliff Gallup. The method of creating the unique Gene Vincent sound is explained at https://www.soundonsound.com/forum/viewtopic.php?t=46533. 

 

Another famous pioneer was Sam Phillips of Sun Studios with his innovative approach to creating studio echo.

 

Studio echo enhances the natural guitar sound and gives it realism. See Chet Atkins - Wheels and medley

 

 

SYSTEM STAGE 7: TREMOLO AND VIBRATO EFFECTS

 

These two important effects were fitted as a built-in standard feature on many mainstream amplifiers from the 1950’s on.

 

One of the earliest exponents was Duane Eddy with numerous tracks like Rebel Rouser and Forty Miles of Bad Road and Ballad of Paladin

 

“Tremolo” modulates the frequency or amplitude. Created by deflecting the string sideways or sliding up and down the fretboard.   Fender perfected the electronic tremolo by eliminating undesirable side-effects.

 

Duane Eddy – Rebel Rouser 1958

Link Wray - Rumble 1958

Tommy James and the Chondelles - Crimson and Clover 1968 (Note the tremolo on voice towards the end of the track)

Jodie Reynolds – Endless Sleep 1958

Jodie Reynolds – Fire of Love – 1958

The Viscounts – Harlem Nocturne – 1965

The Ventures – Yellow Bird    (subtle tremolo with the odd vibrato) and Silver City and Beyond the Reef

The Smiths – How Soon Is Now?

 

“Vibrato” modulates the pitch.

This live recording of Sleepwalk on steel slide guitar from 1959 illustrates the technique.

 

Note: IMHO the original recording of this track is truly a superb performance – musically and electronically – one of the best tracks ever recorded. On CD is hard to beat – just brilliant !!

For those interested there is a detailed discussion about how they may have achieved the sound at      https://bb.steelguitarforum.com/viewtopic.php?t=343343.       Seems nobody actually knows.

My guess is that it may have been directly recorded from the steel guitar with global studio echo added later using multi-track recording. Sun Records had been doing this for several years before that. This recording illustrates the importance of the high amplitude asymmetrical peak signal and its contribution to the final sound. Compare with the less dynamic sound from a Fender Strat - https://www.youtube.com/watch?v=HQjUZ8wZe8s or https://www.youtube.com/watch?v=SEtIK2ZC9Pg  or the compressed sound on this track https://www.youtube.com/watch?v=SS0MuXt7gwg

 

Mechanical lever arms were fitted to most major brand models from the 1950’s on. The Grestch Country Gentleman with Bigsby lever/whammy bar is a fine example of this feature.

Chet Atkins – Dark Eyes and MyTwangyGuitar – The House is Rocking and Smoke Demo

 

A more modern design is shown by Jeff Beck in Apache and Sleepwalk

 

Differences between these effects are explained at https://www.youtube.com/watch?v=_b8WfoAHILA and https://www.youtube.com/watch?v=oKfqRGoUBus and https://www.fender.com/articles/parts-and-accessories/pedal-board-primer-get-to-know-tremolo

 

For a more modern example see Whammy Bar Tricks with John Petrucci of Dream Theater

 

 

SYSTEM STAGE 8: WAH AND WAH WAH EFFECTS PEDALS

 

Early pedals were based on an early Hammond Organ “swell pedal and were simply a foot operated volume control installed between the guitar and the amp. This allowed the player to vary the volume to modulate the signal volume (loudness).

 

One of the best examples of this effect was used for the movie “Shaft” in 1971. Isaac Hayes and The Ventures.

 

The original Wah pedal is said to have been created by Jim Dunlop in 1966

 

Later versions vary the bass and treble tone mix – in other words a foot operated tone control having the bass and treble controls connected inversely – i.e. max treble min bass to max bass to min treble.

 

https://www.youtube.com/watch?v=8FK0z6GUqts

 

See also Wah Techniques: John Petrucci

 

SYSTEM STAGE 9: GAIN, OVERDRIVE, DISTORTION, CRUNCH & FUZZ

These effects were introduced as an integrated feature in amplifiers in the 1960’s as a deliberate method of creating a desirable form of distortion.

 

Explained at https://www.youtube.com/watch?v=_ZxZfbkW86M and https://prosoundhq.com/how-to-get-a-good-crunch-tone-amp-and-guitar-settings/

 

Modern amplifiers either do not include these effects or use solid state circuitry to achieve the result.

 

 

SYSTEM STAGE 10: COMPRESSION AND LIMITING

 

Compression and Limiting have been used in radio broadcasting and recording for nearly a century and by evolution have crept into the guitar industry to appear as a feature in guitar amplifiers to produce particular effects.

 

Compression and Limiting are widely used in AM/FM/DAB broadcasting to minimise modulation bandwidth, in vynil recordings to reduce track amplitude and in CD/DVD/Blue Ray recordings to reduce dynamic range to acceptable levels.

 

The aural effect is to dull the sound as a result of attenuation or elimination of high frequencies needed to create clean tone.

 

Compression also increases the average musical signal power so at high volume will drive the amplifier harder. Proceed at your own risk.

 

Refer https://en.wikipedia.org/wiki/Dynamic_range_compression

 

The sound of this magnificient track – I Can’t Stand the Rain featuring Steve Cropper - is ruined by compression and limiting. Harmonics, dynamic range and presence are subdued. The CD pressing is awesome. Note the subtle vibrato in the background. Some other great tracks are on this album too.

 

 

SYSTEM STAGE 11: THE AMPLIFIER

 

The Amplifier is designed and constructed a system in its own right.

 

This is explained in Section 7.

 

Nominal power output ratings generally increase in 5 Watts bands up to about 30 watts then 10 Watts steps to 100 Watts.

 

The Amplifier and its Power Supply are normally constructed as an integrated unit in guitar amplifiers offering power outputs from about 3-5 Watts rms – e.g. 1 x 6V6GT - to up to about 400 Watts rms – e.g. 8 x KT88 or 6550 tubes.

 

The physical size and weight of the amplifier is very dependent on the choice of power output and size of tubes. If all tubes are 7 or 9 pin miniature types the amplifier can be in a compact form and deliver up to 20-25 Watts rms output using 6BQ5, EL84, 6CZ5 or 6973 9 pin tubes. This class of tube is usually reliable and does not present design issues other than preventing parasitic oscillation.

 

Octal socket tubes range in power output capabilities depending upon B+ voltage and bottle diameter.

 

The EL34/6CA7 pentode can be operated safely and offers a standard bottle for up to 100 Watts rms output at 800 VDC Plate volts, whereas the KT88 is significantly larger in diameter, requires more chassis space and offers a large diameter bottle for up to 100 Watts rms output at 600 VDC Plate volts. To avoid issues with parasitic oscillation and thermal runaway the DC Screen Grid voltage should always be kept as low as possible – ideally not more than 50% of the Plate voltage.

 

This class of tube is normally very reliable if not pushed, but when driven hard at excessive voltages trouble is guaranteed.

For a real-world experience this commentary is recommended to study carefully: Rig Rundown - AC/DC's Angus Young & Stevie Young

To ensure reliability it is not advisable to apply more than about 600 VDC to an octal socket. Tracking between pins can develop over time.

 

For appearance reasons a separate Amplifier head unit should match the same width as the speaker cabinet it sits on. Cabinets typically come in 2 inch increments, with 24 inches being a practical maximum for weight, handling, transport and stage space. A 24 inch wide cabinet will accommodate speaker drivers up to 18 inches diameter or 4 x 10 inch drivers. A 24 inch wide Amplifier head will accommodate most standard Amplifier designs.

 

Beyond that power level the chassis and transformers become too large and heavy to handle conveniently so the Amplifier and Power Supply are separated into discrete units connected together with insulated cables. This form of construction is extreme and would be rarely seen in live work. The Wolff Insanity Brownout 1000 amplifier is one such example.

 

19 inch rack mounting would be a logical way to go for a high-power unit but would require even more space – one rack case for the Power Supply, one rack case for the Amplifier and one rack case for the Pre-amplifier and driver tubes.

 

Other alternatives using transmitting tubes require very high B+ voltages that become impracticable for normal use.

 

In this modern era, professional in-house PA systems will be all solid-state because of the higher power to weight/size ratio of solid state amplifiers v tube amplifiers.

 

Class D solid-state amplifiers are now displacing their Class AB solid-state predecessors for large installations but cannot deliver sound quality comparable to tubes. This means that much of the effort that goes into achieving the live tube sound by the guitarist is “lost in the system”. Unfortunately the general trend to compressed digital sound, small size, low weight and low cost is pushing tube amps out of reach of the dedicated guitarist. Such is progress.

 

 

SYSTEM STAGE 12: THE LOUDSPEAKER

 

The Loudspeaker could be the most important component in the entire system because the sound it produces is the sound you actually hear.

 

Consequently, the choice of loudspeaker must be made with care.

 

 

SYSTEM STAGE 13: APPEARANCE

It is an axiom of engineering practice that a component or complete device must look attractive.

This rule also applies to guitar amplifiers.

No self-respecting guitarist will be seen on-stage with a PA Amplifier, or PA Mixer Amplifier, or a basic open chassis amp without a cabinet, as his or her amp choice – even when it will do the job well. The guitar amplifier must look like a guitar amplifier. However history shows it is OK to use a Bass amplifier so long as it looks the part.

If you are making the system yourself ensure the amplifier chassis will aesthetically match the speaker cabinet requirements to present a professional looking unit.

If it does not look good then it is unlikely to work well, so abandon it and start again.

 

THE FINAL SYSTEM CONFIGURATION

These video presentations from Joe Bonamassa describe the elements of a system and how they interact       

[2018]         https://www.youtube.com/watch?v=rNvOUmwPiUQ

[2022]         https://www.youtube.com/watch?v=GuVfNjuz2XM

 

In contrast, Eric Clapton offers a simpler system    https://www.youtube.com/watch?v=ZoAp0xmI8gw

and Brian May                https://www.youtube.com/watch?v=jJ_OamX-PA8

 

For a cleaner system sound see           https://www.youtube.com/watch?v=YhS8bCs12N8 and https://www.youtube.com/watch?v=Dyi2MKjs-kM

 

 



 

REMEMBER - ALWAYS TAKE CARE WHEN WORKING WITH HIGH-VOLTAGE - DEATH IS PERMANENT!!
 

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This page last modified 12 July 2023
 

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