3.3 Leslie Speaker / Rotary Effect

Rotary Speaker

  • The Leslie speaker is a combined amplifier and loudspeaker that modifies the sound of an instrument as well as amplifying it, by rotating sound waves. It is most commonly associated with the Hammond organ, though it was later used for the guitar and other instruments.
  • A typical Leslie speaker contains an amplifier, treble and bass speaker, though specific components depend on the model. Control is achieved either by an external half-moon switch, or by a foot pedal, that alternates between two settings known as “chorale” and “tremolo”.
  • The speaker is named after its inventor, Donald Leslie. Leslie began working in the late 1930s to get a speaker for a Hammond organ that had a closer emulation of a pipe or theatre organ, and discovered that rotating sound gave the best effect. Hammond was not interested in marketing or selling the speakers, so Leslie sold them himself as an add-on, targeting other organs as well as Hammond. The first speaker was made in 1941. The sound of the organ being played through his speakers received national radio exposure across the US, and it became a commercial and critical success as an essential part of any jazz organist.
  • Because the Leslie is a sound modification device in its own right, various attempts have been made to emulate the effect using electronics. The Univox Uni-Vibe was used by a number of notable musicians, while the Neo Ventilator has received critical praise, and Hammond-Suzuki now manufacture their own simulator in a box.
  • A Leslie speaker consists of a number of individual components. The audio signal enters the amplifier from the instrument. Once amplified, the signal travels to an audio crossover, where it is split into separate frequency bands that can be individually routed to each loudspeaker.
  • Different models have different combinations of speakers, but the most common model, the 122, consists of a single woofer for bass and tweeter for treble. The audio emitted by the speakers is isolated inside an enclosure, aside from a number of outlets which lead towards either a rotating horn or drum. Both the horn and the drum are rotated at a constant speed by an electric motor.
  • The only control common to all Leslie speakers is a dial controlling the master volume. This is normally set up once and then left, since the volume is designed to be controlled by the organ’s expression pedal. Leslie recommended playing the organ at full volume with all stops or drawbars pulled out and adjusting the volume just before distortion occurs. However, the distorted sound of an overdriven vacuum tube amplifier can be a desirable sound, to the extent that modern Leslie simulators have an explicit “overdrive” setting. The half-moon switch on a Hammond organ that changes setting on the Leslie speaker between “chorale” and “tremolo”
  • Unlike most popular music amplifiers, that use jack plugs to connect to instruments, Leslie speakers use an amphenol connector to interface directly to an organ via a console connector. Older models that used tube power amplifiers used a variety of 6-pin connectors, while later models used a 9-pin connector. In all cases, for a single organ – Leslie configuration, the mains power, audio and control signals are all carried on the connector, and the design of the pin layouts varies between organs and speakers. It is also possible to connect multiple Leslie speakers to a single organ, by using a power relay that provides the necessary AC current. A separate device known as the combo preamp is necessary to connect a vintage Leslie to another instrument such as a guitar. This combines a separate AC input and line level input onto a single amphenol connector, and provide a footswitch to select between the speeds of the Leslie.
  • The Leslie is specifically designed, via reproduction of the Doppler effect, to alter or modify sound. As the sound source is rotated around a specific pivot point, it produces tremolo (the modulation of amplitude) and a variation in pitch. This produces a sequence of frequency modulated sidebands. To stop a Leslie’s rotor, a special brake circuit was added to the Leslie motor controls, that incorporated an electronic relay by producing a half-wave of direct current.
  • Much of the Leslie’s unique tone is due to the fact that the system is at least partially enclosed, whereby linear louvres along the sides and front of the unit can vent the sound from within the box after the sound has bounced around inside, mellowing it. The crossover is deliberately set to 800 Hz to give the optimum balance between the horn and the drum, and is considered an integral part of the speaker. The tone is also affected by the wood used. Tone differences, due to cost cutting using particle board for speaker and rotor shelves instead of the previous plywood, are evident in the Leslie’s sound. The thinner ply of the top of the cabinet adds a certain resonance as well. Like an acoustic instrument, a Leslie’s tone is uniquely defined by its cabinet design and construction, the amplifier, crossover and speakers used, and the motors — not merely by the spinning of rotors.
  • Because a Leslie speaker modifies as well as amplifies the sound, the output cannot simply be connected to a larger PA system if the volume onstage from the built-in amplifier is too quiet. This is particularly problematic for an older Leslie like the 122 or 147, which only has a 40 watt RMS power amplifier. Instead, microphones are placed around the Leslie, and the output from these is connected to the PA.
  • The Beatles first recorded using a Leslie during the sessions for Revolver in 1966. After John Lennon had asked for his voice to sound “as though I’m the Dalai Lama singing from the highest mountain top”, Abbey Road engineer Geoff Emerick rewired the input of the studio’s Leslie so a vocal microphone could be attached to it. Emerick used this setup to record Lennon’s vocal on the track “Tomorrow Never Knows” and claims the Beatles subsequently wanted to record everything through a Leslie. George Harrison played his guitar through a Leslie on “Lucy in the Sky with Diamonds” and “You Never Give Me Your Money”. The Beatles subsequently inspired other guitarists to use the speaker. Eric Clapton played through one on Cream’s song “Badge”, and David Gilmour used a similar setup when recording with Pink Floyd.

1.12 Distortion


  • Distortion is created by turning the volume of a sound up too loud.
  • It is primarily a guitar effect, created using a pedal or stompbox, or a DAW plugin
  • We can control three parameters of a distortion effect:
Gain The volume of the input signal (before distortion)
Output The volume of the output signal (after distortion)
Tone Changes the frequency content of the output
  • Historically, artists created distortion by damaging their amplifiers
  • When the gain is increased, the wave peaks and troughs are clipped
  • Soft clipping rounds the tops of the waves and sounds warmer. It is often seen in valve amps. Hard clipping creates a wave with square peaks & troughs and sounds harsher; it is commonly seen in transistor amps.


  • The distorted signal has more harmonics, and filtering / EQ may be required to fit it well into the mix.



  • Fuzz is a dense distortion used by guitarists such as Jimi Hendrix

Jimi Hendrix – Purple Haze


  • Overdrive gives the sound more crunch.
  • It was originally created by pushing amps to play louder than they were able to

Chuck Berry – Johnny B. Goode

Bit Distortion

  • Lowering the bit depth leads to distortion of audio


  • The track can sound ‘electronic’ or ‘lo-fi’


La Roux – Colourless Colour

Modelling Distortion

  • We can use plugins to model the sound of distortion
  • Software plugins include Logic’s ‘Overdrive’ and ‘Bitcrusher’
  • We can also use hardware to emulate the sound of different distortions and amplifiers
  • Line6’s Pod emulates the sound of many different guitar rigs
  • This is beneficial as it means that you can have the option of lots of different amplifier settings without needing to own or transport the physical amplifiers


1.12 LFOs

Using LFOs

  • An LFO is a low frequency oscillator
  • The frequencies used are below 20Hz, so they are inaudible
  • An LFO changes a parameter of an effect or processor according to another wave
  • Examples might be altering the delay time according to a sine wave. Other geometric waves can be used to change the effect of an LFO (e.g. square/triangle/pulse)


Controls on Modulation Effects

  • Modulation effects have controls related to the rate and the depth of the modulation
  • Rate is how fast the periodic change of the parameter takes place (wave frequency)
  • Depth is how much the parameter is varied (wave amplitude)
  • The combination of both of these parameters can change whether the effect sounds subtle or very obvious


Comb Filtering


  • A comb filter adds a delayed version of a signal to itself, causing constructive and destructive interference.
  • The frequency response of a comb filter consists of a series of regularly spaced notches, giving the appearance of a comb.


Historical Production of Modulation Effects


Leslie Speaker


  • The Leslie speaker uses the Doppler Effect to create modulation, and is sometimes called ‘Rotary’ on effect plugins.
  • This is similar to the changing pitch heard when an ambulance passes you
  • It is a system of rotating speakers used primarily with the Hammond Organ in the 1960s
  • It occurs because the source of a sound changes position, relative to the listener.

The Eagles – Hotel California

The Beatles – Let It Be

Tape-Based Origins of Modulation Effects

  • Modulation effects were originally created by using two tape recorders


1.12 Introduction to Reverb

Reverb is short for reverberation. This is a natural acoustic phenomenon where sound bounces off surfaces in a space and tells our brain lots of details about where we are. Throughout the history of music recording and production, it has been crucial for us to gain control over this and ensure that we can add or remove ambience to recordings where the space doesn’t necessarily sound how we want it to.

Echo Chambers

  • Originally, reverb was created through a variety of ‘live rooms’ that had very different sounding reverb characteristics.
  • This was expensive, and engineers soon found ways of recreating these reverbs in other forms in smaller rooms.
  • One way was to find a very reverberant room and replay your mix on speakers in that room, using a pair of omnidirectional microphones to record the resulting echoes.
  • Some studios used reverberant spaces they already had – for example the office toilet!

The Crystals – Da Doo Ron Ron

Tina Turner – River Deep Mountain High

Plate Reverb and Spring Reverb

  • Plate and spring reverb are both methods of artificial reverb production devised in the 1950s.
  • Both used the vibration of metal objects to create the sound of reverb
  • Plate reverb was often used in studios and avoided the need for an echo chamber.
  • Spring reverb was often used in amplifiers; Fender was one of the first manufacturers to build spring reverb into their amps.

Beach Boys – God Only Knows


A Simple Plate Reverb

Plate reverb.png

A Simple Spring Reverb


Digital Reverb


  • Digital reverb was first seen in effect units made by Yamaha and Lexicon in the 1980s
  • It models a reverb by using lots of delays, which are mathematically calculated
  • Digital reverbs enabled users and manufacturers to store lots of presets
  • As computer processors got faster in the 1990s, digital reverb was incorporated as a software plugin

En Vogue – Hold On


Convolution Reverb

  • Convolution reverb reproduces a real reverb from a real space, and was pioneered by Sony in 1996
  • An impulse reflex is generated in a space, and the response is recorded
  • Mathematical algorithms subtract the impulse reflex from the reverb and this can then be applied to other sounds
  • Convolution reverb is very heavy on processor usage


Other Types of Reverb

  • Reverse reverb is created using a wet reverb signal played backwards. The original recording is then played forwards with the reverb which is first.

Beach Boys – Feel Flows

The Only Ones – Miles From Nowhere

Gated Reverb

  • In many styles of music, but particularly the 1980s, the reverb decay was gated, which meant that a very dense reverb could be used without causing ‘muddiness’ in the mix. Gated reverb is often used on snare drums and sometimes vocals.

Phil Collins – In The Air Tonight

Edexcel Music Technology 2017 Resources

I am currently working on a number of resources for the new specification in Music Technology (for first teaching in 2017-18).

To be released by mid-February (keep visiting this site for more information0

Full Content Guide for Edexcel AS and A Level Music Technology 2017

Guide to all content to be delivered for the course; suitable for teachers or for student revision.

Student Workbook for Edexcel AS and A Level Music Technology 2017

Suitable for use in lessons and for recording notes / key terminology.

Component 3 Practice Paper Pack

Three practice papers with mark schemes and links to audio files. 

Component 4 Practice Paper Pack

Three practice papers with specially written audio tracks with mark schemes.

Understanding Recording and Production Technology

As part of studying for and teaching the Edexcel A Level Music Technology course, it is important that students develop their knowledge of chronology and different recording media.

In the specification, it states that students are required to develop knowledge and understanding of the history and development of recording and production technology, from current digital technologies back to the mono, analogue recording technologies in the 1930s, through the following eras:

  • Digital audio workstations (DAW) and emerging technologies (c.1996 – present day)
  • Digital recording and sequencing (c.1980 – present day)
  • Large-scale analogue multitrack (c.1969 – 1995)
  • Early multitrack recording (c.1964 – 1969)
  • Direct to tape mono recording (c.1930 – 1963)

Thus, it is useful to start with the following key developments in recording technology, and that students revisit this as part of their revision for the Edexcel A Level Music Technology course.

It would also be beneficial to focus on the following developments in recording technology, and to place these into context when listening to music.

  • Phonautograph / wax cylinder / phonograph / player pianos (pre 1900)
  • Gramophones / 78s (pre 1900) (for context)
  • Development of early tape / microphone / amplification technology (1910 – )
  • LP / Vinyl (late 1940s)
  • Stereo / microphone design (1950s)
  • Multitrack tape – knowledge of 4 / 8 / 16 / 24 tracks (1960s – )
  • Cassette tape (1960s)
  • Effects and processing / experimentation (1960s / 1970s)
  • CD (1980s)
  • Digital and computer-based studios (1990s)
  • MP3 / Napster (early 2000s)
  • iTunes / iPod (mid-2000s)
  • ‘The Cloud’ / streaming facilities (2010 – )

For each bit of technology consider:

  • Technical capabilities created
  • Impact on music and recording
  • First proponents (if applicable)

Good luck with your revision and study in A Level Music Technology!

New Specification: Music Technology 2017

2017 is an exciting time to be a student or teacher of A Level Music Technology. There is a new Edexcel specification that allows students to develop a deeper understanding of the technical and theoretical aspects of the content and a slimmed down coursework requirement.

This also marks a huge change in the A Level Music Technology qualification and beyond, with significant reform across the board. Ultimately, the biggest change is that AS level courses are now completely ‘decoupled’ from the overall A Level. This means that marks achieved in the AS course will not contribute towards the A level, and thus students only actually need to sit the A level in Year 13, with no requirement to be assessed by the exam board in Year 12.

Ultimately, this means there are decisions to make on a centre-wide basis; do schools and colleges enter candidates for both AS and A Level or spend the two years teaching the A Level course? I personally believe the two year A Level Music Technology course has the potential to allow much more flexibility to teach the appropriate skills and knowledge/understanding necessary for success in the qualification. For example, a centre could choose to deliver just the A Level course and devise their own course structure in the first year of sixth form. This could be carefully tailored to the learning needs of the students.

Alternatively, students in Year 12 could sit the AS and then the entire A Level in Year 13. Many AS and A level courses are designed to be co-teachable, and the Edexcel A Level Music Technology 2017 course is no exception. This means that the AS content is a subset of the overall A Level content and enables you to teach both Year 12 and Year 13 students in one group, with some stretch and challenge / extension for the Year 13 learners who have previously built up further understanding of the subject and are able to apply this in context.

Centres who choose to sit AS and A Level will need to sit all components for both the AS and A level; students sitting the A Level will need to sit A Level Components 1-4 in the academic year they will be sitting the examination.

Only time will tell which is the best solution; this, however, remains heavily dependent on the course and students involved.