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Bristol Emulations

This is a write-up of each of the emualated synthesisers. The algrithms employed were 'gleaned' from a variety of sources including the original owners manuals, so they may be a better source of information. Some of them were built just from descriptions of their operation, or from understanding how synths work - most of them were based on the Mini Moog anyway. Many of the synths share components: the filter covers most of them, the Prophets and Oberheims share a common oscillator and the same LFO is used in many of them. Having said that each one differs considerably in the resulting sound that is generated, more so than initially expected. Considering the shared filter, the reason they all have such distinctive sounds is that the original instruments used different modulations and mod routing. Each release refines each of the components and the result is that all emulations benefit from the improvements.

The write-up includes the parameter operations, modulations, a description of the original instrument and a brief list of the kind of sounds you can expect by describing a few of the well known users of the synth.

All emulations are available from the same engine, just launch multiple GUIs and adjust the midi channels for multi timbrality and layering.

It is noted here that the engine is relatively 'dumb'. Ok, it generates a very broad range of sounds, currently about 15 different synthesisers and organs, but it is not really intelligent. Memories are a part of the GUI specification - it tells the engine which algorithm to use on which MIDI channel, then it calls a memory routine that configures all the controllers and a side effect of setting the controllers is that the values are sent to the engine. This is arguably the correct model but it can affect the use of MIDI master keyboards. The reason is that the GUI is really just a master keyboard for the engine and drives it with MIDI SYSEX messages over TCP sessions. If you were to alter the keyboard transpose, for example, this would result in the GUI sending different 'key' numbers to the engine when you press a note. If you were already driving the synth from a master keyboard then the transpose button in the Brighton GUI would have no effect - the master keyboard would have to be transposed instead. This apparant anomaly is exacerbated by the fact that some parameters still are in the engine, for example master tuning is in the engine for the pure fact that MIDI does not have a concept of master tuning (only autotuning). Irrespective of this, bristol is a synthesiser so it needs to be played, tweaked, driven. If you think that any of the behaviour is anomalous then let me know. One known issue in this area is that if you press a key, transpose the GUI, then release the key - it will not go off in the engine since the GUI sends a different key code for the note off event - the transposed key. This cannot be related to the original keypress. This could be fixed with a MIDI all notes off event on 'transpose', but I don't like them. This effect is also in part due to the Brighton model for the keyboard - you have to click a key 'on', and then click it 'off' again. There have been requests for key-off on button release, but this prevents you playing chords from the GUI. Perhaps it should be a GUI option, your input would be appreciated.

Moog Mini

It is perhaps not possible to write up who used this synth, the list is endless. Popular as it was about the first non-modular synthesiser, built as a fixed configuration of the racked or modular predecessors.

Best known at the time on Pink Floyd 'Dark Side of the Moon' and other albums. Rick Wakefield used it as did Jean Michel Jarre. Wakefield could actually predict the sound it would make by just looking at the settings, nice to be able to do if a little unproductive but it went to show how this was treated as an instrument in its own right. It takes a bit of work to get the same sweet, rich sounds out of the emulation, but it can be done with suitable tweaking.

The original was monophonic, although a polyphonic version was eventually made after Moog sold the company - the MultiMoog. This emulation is more comparable to that model as the sound is a bit thinner and can be polyphonic. The design of this synth became the pole bearer for the following generations: it had three oscillators, one of which could become a low frequency modulator. They were fed into a mixer with a noise source, and were then fed into a filter with 2 envelope generators to contour the wave. Modulation capabilities were not extensive, but interestingly enough it did have a frequency modulation (FM) capability, eventually used by Yamaha to revolutionise the synthesiser market starting the downfall of analogue systhesis twenty years later.

All the analogue synths were temperature sensitive. It was not unusual for the synths to 'detune' between sound test and performance as the evening set in. To overcome this they could optionally produce a stable A-440Hz signal for tuning the oscillators manually - eventually being an automated option in the newer synths. Whilst this digital version has stable frequency generation the A-440 is still employed here for the sake of it.

Modifiers and mod routing are relatively simple, Osc-3 and noise can be mixed, and this signal routed to the oscillator 1 and 2 frequency or filter cutoff.

The synth has 5 main stages as follows:

Control

Master tuning: up/down one note.

Glide: (glissando, portamento). The rate at which one key will change its frequency to the next played key, 0 to 30 seconds.

Mod: source changes between Osc-3 and noise.

Release: The envlope generators had only 3 parameters. This governed whether a key would release immediately or would use Decay to die out.

Multi: Controls whether the envelope will retrigger for each new keypress.

Oscillators

There are three oscillators. One and two are keyboard tracking, the third can be decoupled and used as an LFO modulation source.

Oscillator 1:

        Octave step from 32' to 1'.
        Waveform selection: sine/square/pulse/ramp/tri/splitramp
        Mod: controls whether Osc-3/noise modulates frequency

Oscillator 2:

        Octave step from 32' to 1'.
        Fine tune up/down 7 half notes.
        Waveform selection: sine/square/pulse/ramp/tri/splitramp
        Mod: controls whether Osc-3/noise modulates frequency

Oscillator 3:

        Octave step from 32' to 1'.
        Fine tune up/down 7 half notes.
        Waveform selection: sine/square/pulse/ramp/tri/splitramp
        LFO switch to decouple from keytracking.

Mixer

Gain levels for Oscillator 1/2/3
Mixing of the external input source into filter Noise source with white/pink switch.

Note: The level at which Osc-3 and noise modulates sound depends on its gain here, similarly the noise. The modulator mix also affects this, but allows Osc-3 to mod as well as sound. The modwheel also affect depth.

Filter

Cutoff frequency

Emphasis (affects Q and resonance of filter).

Contour: defines how much the filter envlope affects cutoff.

Mod - Keyboard tracking of cutoff frequency.

Mod - Osc-3/noise modulation of cutoff frequency.

Contour

The synth has two envelope generators, one for the filter and one for the amplifier. Release is affected by the release switch. If off the the sound will release at the rate of the decay control.

Attack: initial ramp up of gain.

Decay: fall off of maximum signal down to:

Sustain: gain level for constant key-on level.

Key: Touch sensitivity of amplifier envelope.

Improvements to the Mini would be some better oscillator waveforms, plus an alternative filter as this is a relatively simple synthesiser and could do with a warmer filter.

The Output selection has a Midi channel up/down selector and memory selector. To read a memory either use the up/down arrows to go to the next available memory, or type in a 3 digit number on the telephone keypad and press 'L' for load or 'S' for save.

Moog Voyager (Bristol "Explorer")

This was Robert Moog's last synth, similar in build to the Mini but created over a quarter of a century later and having far, far more flexibility. It was still monophonic, a flashback to a legendary synth but also a bit like Bjorn Borg taking his wooden tennis racket back to Wimbledon long after having retired and carbon fibre having come to pass. I have no idea who uses it and Bjorn also crashed out in the first round. The modulation routing is exceptional if not exactly clear. The emulation currently (release 0.9) does not have the same filter operation - the original has two resonant low pass filters layered on top of each other, this still needs to be completed.

The Voyager, or Bristol Explorer, is definately a child of the Mini. It has the same fold up control panel, three and half octave keyboard and very much that same look and feel. It follows the same rough design of three oscillators mixed with noise into a filter with envelopes for the filter and amplifier. In contrast there is an extra 4th oscillator, a dedicated LFO bus also Osc-3 can still function as a second LFO here. The waveforms are continuously selected, changing gradually to each form. The envelopes are 4 stage rather than the 3 stage Mini, and the effects routing bears no comparison at all being far more flexible here.

Just because its funny to know, Robert Moog once stated that the most difficult part of building and releasing the Voyager was giving it the title 'Moog'. He had sold his company in the seventies and had to buy back the right to use his own name to release this synthesiser as a Moog, knowing that without that title it probably would not sell quite as well.

Control

LFO: Frequency Sync: LFO restarted with each keypress.

Fine tune +/- one note
Glide 0 to 30 seconds.

Modulation Busses:

Two busses are implemented. Both have similar capabilities but one is controlled by the mod wheel and the other is constantly on. Each bus has a selection of sources, shaping, destination selection and amount.

Wheel Modulation: Depth is controller by mod wheel.

        Source: Triwave/Ramp/Sample&Hold/Osc-3/External
        Shape: Off/Key control/Envelope/On
        Dest: All Osc Frequency/Osc-2/Osc-3/Filter/FilterSpace/Waveform (*)
        Amount: 0 to 1.

Constant Modulation: Can use Osc-3 as second LFO to fatten sound.

        Source: Triwave/Ramp/Sample&Hold/Osc-3/External
        Shape: Off/Key control/Envelope/On
        Dest: All Osc Frequency/Osc-2/Osc-3/Filter/FilterSpace/Waveform (*)
        Amount: 0 to 1.

        * Destination of filter is the cutoff frequency. Filter space is the 
        difference in cutoff of the two layered filters. Waveform destination 
        affects the continuously variable oscillator waveforms and allows for 
        Pulse Width Modulation type effects with considerably more power since
        it can affect ramp to triangle for example, not just pulse width.

Oscillators

Oscillator 1:

        Octave: 32' to 1' in octave steps
        Waveform: Continuous between Triangle/Ramp/Square/Pulse

Oscillator 2:

        Tune: Continuous up/down 7 semitones.
        Octave: 32' to 1' in octave steps
        Waveform: Continuous between Triangle/Ramp/Square/Pulse

Oscillator 3:

        Tune: Continuous up/down 7 semitones.
        Octave: 32' to 1' in octave steps
        Waveform: Continuous between Triangle/Ramp/Square/Pulse

Sync: Synchronise Osc-2 to Osc-1
FM: Osc-3 frequency modulates Osc-1 KBD: Keyboard tracking Osc-3
Freq: Osc-3 as second LFO

Mixer

Gain levels for each source: Osc-1/2/3, noise and external input.

Filters

The filters are two layered resonant lowpass filters.

Cutoff: Frequency of cutoff
Space: Distance between the cutoff of the two layered filter. Resonance: emphasis/Q.
KBD tracking amount
Velocity: On/Off keyboard velocity tracking.

Envelopes

Attack
Decay
Sustain
Release

Amount to filter (positive and negative control)

Velocity sensitivity of amplifier envelope.

Master

Volume
LFO: Single LFO or one per voice (polyphonic operation). Glide: On/Off portamento
Release: On/Off envelope release.

The Explorer has a control wheel and a control pad. The central section has the memory section plus a panel that can modify any of the synth parameters as a real time control. Press the first mouse key here and move the mouse around to adjust the controls. Default values are LFO frequency and filter cutoff but values can be changed with the 'panel' button. This is done by selecting 'panel' rather than 'midi', and then using the up/down keys to select parameter that will be affected by the x and y motion of the mouse. At the moment the mod routing from the pad controller is not saved to the memories, and it will remain so since the pad controller is not exactly omnipresent on MIDI master keyboards - the capabilities was put into the GIU to be 'exact' to the design.

This synth is amazingly flexible and difficult to advise on its best use. Try starting by mixing just oscillator 1 through to the filter, working on mod and filter options to enrich the sound, playing with the oscillator switches for different effects and then slowly mix in oscillator 2 and 3 as desired.

Memories are available via two grey up/down selector buttons, or a three digit number can be entered. There are two rows of black buttons where the top row is 0 to 4 and the second is 5 to 9. When a memory is selected the LCD display will show whether it is is free (FRE) or programmed already (PRG).

Fender Rhodes

Again not an instrument that requires much introduction. This emulation is the DX-7 voiced synth providing a few electric piano effects. The design is a Mark-1 Stage-73 that the author has, and the emulation is reasonable if not exceptional. The Rhodes has always been widely used, Pink Floyd on 'Money', The Doors on 'Riders on the Storm', Carlos Santana on 'She's not There', everybody else in the 60's.

The Rhodes piano generated its sound using a full piano action keyboard where each hammer would hit a 'tine', or metal rod. Next to each rod was a pickup coil as found on a guitar, and these would be linked together into the output. The length of each tine defined its frequency and it was tunable using a tight coiled spring that could be moved along the length of the tine to adjust its moment. The first one was built mostly out of aircraft parts to amuse injured pilots during the second world war. The Rhodes company was eventually sold to Fender and lead to several different versions, the Mark-2 probably being the most widely acclaimed for its slightly warmer sound.

There is not much to explain regarding functionality. The emulator has a volume and bass control, and one switch that reveals the memory buttons and algorithm selector.

The Rhodes would improve with the addition of small amounts of either reverb or chorus, potentially to be implemented in a future release.

The Rhodes Bass was cobbled together largely for a presentation on Bristol. It existed and was used be Manzarek when playing with The Doors in Whiskey-a-GoGo; as the owner specified that whilst the music was great they needed somebody playing the bass. Rather than audition for the part Manzarek went out and bought a Rhodes Bass and used it for the next couple of years.

Hammond (modular)
Hammond B3 (dual manual)

The author first implemented the Hammond module, then extended it to the B3 emulation. Users of this are too numerous to mention and the organ is still popular. Jimmy Smith, Screaming Jay Hawkins, Kieth Emerson, Doors and almost all american gospel blues. Smith was profuse, using the instrument for a jazz audience, even using its defects (key noise) to great effect. Emerson had two on stage, one to play and another to kick around, even including stabbing the keyboard with a knife to force keylock during performances (Emerson was also a Moog fan with some of the first live performances). He also used the defects of the system to great effect, giving life to the overdriven Hammond sound.

The Hammond was historically a mechanical instrument although later cheaper models used electronics. The unit had a master motor that rotated at the speed of the mains supply. It drove a spindle of cog wheels and next to each cog was a pickup. The pickup output went into the matrix of the harmonic drawbars. It was originally devised to replace the massive pipe organs in churches - Hammond marketed ther instruments with claims that they could not be differentiated from the mechanical pipe equivalent. He was taken to court by the US government for misrepresentation, finally winning his case using a double blind competitive test against a pipe organ, in a cathedral, with speakers mounted behind the organ pipes and an array of music scholars, students and professionals listening. The results spoke for themselves - students would have scored better by simply guessing which was which, the professionals fared only a little better than that. The age of the Hammond organ had arrived.

The company had a love/hate relationship with the Leslie speaker company - the latter making money by selling their rotary speakers along with the organ to wide acceptance. The fat hammond 'chorus' was a failed attempt to distance themselves from Leslie. That was never achieved due to the acceptance of the Leslie, but the chrous did add another unique sound to the already awesome instrument. The rotary speaker itself still added an extra something to the unique sound that is difficult imagine one without the other. It has a wide range of operating modes most of which are included in this emulator.

Parameterisation of the first B3 window follows the original design:

Leslie: Rotary speaker on/off
Reverb: Reverb on/off (*)
VibraChorus: 3 levels of vibrato, 3 of chorus. Bright: Added upper harmonics to waveforms.

only operates when Leslie is active

Lower and Upper Manual Drawbars: The drawbars are colour coded into white for even harmonics and black for odd harmonics. There are two subfrequencies in brown. The number given here are the length of organ pipe that would correspond to the given desired frequency.

16 - Lower fundamental
5 1/4 - Lower 3rd fundamental

    8     - Fundamental
    4     - First even harmonic
    2 2/3 - First odd harmonic
    2     - Second even harmonic

1 3/5 - Second odd harmonic
1 1/7 - Third odd harmonic
1 - Third even harmonic

The drawbars are effectively mixed for each note played. The method by which the mixing is done is controlled in the options section below. There were numerous anomalies shown by the instrument and most of them are emulated.

The Hammond could provide percussives effect the first even and odd harmonics. This gave a piano like effect and is emulated with Attack/Decay envelope.

Perc 4' - Apply percussive to the first even harmonic Perc 2 2/3' - Apply percussive to the first odd harmonic Slow - Adjust rate of decay from about 1/2 second to 4 seconds.

Soft - Provide a soft attack to each note.

The soft attack was an attempt to reduce the level of undesired key noise. The keyboard consisted of a metal bar under each key that made physical contact with 9 sprung teeth to tap off the harmonics. The initial contact would generate noise that did not really accord to the pipe organ comparison. This was reduced by adding a slow start to each key, but the jazz musicians had used this defect to great effect, terming it 'key click' and it became a part of the Hammond characteristics. Some musicians would even brag about how noisy there organ was.

On the left had side are three more controls:

Volume potentiometer

Options switch discussed below.

Rotary Speed: low/high speed Leslie rotation. Shifts between the speeds are supressed to emulate the spin up and down periods of the leslie motors.

The options section, under control of the options button, has the parameters used to control the emulation. These are broken into sections and discussed individually.

Leslie

The Leslie rotary speaker consisted of a large cabinet with a bass speaker and a pair of high frequency air horns. Each were mounted on its own rotating table and driven around inside the cabinet by motors. A crossover filter was used to separate the frequencies driven to either speaker. Each pair was typically isolated physically from the other. As the speaker rotated it would generate chorus type effects, but far richer in quality. Depending on where the speaker was with respect to the listener the sound would also appear to rotate. There would be different phasing effects based on signal reflections, different filtering effects depending on where the speaker was in respect to the cabinet producing differences resonances with respect to the internal baffling.

Separate
Sync: No Bass:
The Leslie had two motors, one for the horns and one for the voice coil speaker. These rotated at different speeds. Some players preferred to have both rotate at the same speed, would remove the second motor and bind the spindles of each speaker table, this had the added effect that both would also spin up at the same rate, not true of the separated motors since each table had a very different rotary moment. The 'No Bass' option does not rotate the voice coil speaker. This was typically done since it would respond only slowly to speed changes, this left just the horns rotating but able to spin up and down faster.
Brake: Some cabinets had a brake applied to the tables such that when the motor stopped the speakers slowed down faster.

X-Over:

        This is the cross over frequency between the voice coil and air horns.
        Uses a butterworth filter design.

Inertia: Rate at which speaker rotational speed will respond to changes.
Overdrive: Ammount by which the applifier is overdriven into distortion.

H-Depth/Frequency/Phase
L-Depth/Frequency/Phase

        These parameters control the rotary phasing effect. The algorithm used
        has three differently phased rotations used for filtering, phasing and
        reverberation of the sound. These parameters are used to control the
        depth and general phasing of each of them, giving different parameters
        for the high and low speed rotations. There are no separate parameters
        for the voice coil or air horns, these parameters are for the two
        different speeds only, although in 'Separate' mode the two motors will
        rotate at slightly different speeds.

Chorus

V1/C1 - Lowest chorus speed
V2/C2 - Medium chorus speed
V3/C3 - High chorus speed

Percusion

Decay Fast/Slow - controls the percussive delay rates. Attack Slow Fast - Controls the per note envelope attack time.

The percussives are emulated as per the original design where there was a single envelope for the whole keyboard and not per note. The envelope will only restrike for a cleany pressed note.

Finally there are several parameters affecting the sine wave generation code. The Hammond used cogged wheels and coil pickups to generate all the harmonics, but the output was not a pure sine wave. This section primarily adjusts the waveform generation:

Preacher: The emulator has two modes of operation, one is to generate the harmonics only for each keyed note and another to generate all of them and tap of those required for whatever keys have been pressed. Both work and have different net results. Firstly, generating each note independently is far more efficient than generating all 90 odd teeth, as only a few are typically required. This does not have totally linked phases between notes and cannot provide for signal damping (see below). The Preacher algorithm generates all harmonics continuously as per the original instrument. It is a better rendition at the expense of large chunks of CPU activity.
Compress: Compress the sine wave to produce a slightly flatter peak.
Bright: Add additional high frequency harmonics to the sine.
Click: Level of key click noise
Reverb: Amount of reverb added by the Leslie
Damping: If the same harmonic was reused by different pressed keys then its net volume would not be a complete sum, the output gain would decay as the pickups would become overloaded. This would dampen the signal strength. This is only available with the Preacher algorithm.

Improvements would come with some other alterations to the sine waveforms and some more EQ put into the leslie speaker. The speaker needs to be changed such that it is permanantly engaged. Currently it has two speeds and on/off, and this is arguably incorrect, it needs three speeds, one of which is zero and then apply acceleration between each of them. This is reasonably easy to do but is not currently implemented.

The net emulation is reasonable, it is distinctively a Hammond sound although it does not have quite as much motor or spindle noise. It could do with a better amplifier emulation for overdrive and could do with more balls at the low end so an integrated EQ would work well here.

The damping algorithms is not quite correct, it has dependencies on which keys are pressed (upper/lower manual). Options drop shadow is taken from the wrong background bitmap so appears in an inconsistent grey.

Vox Continental

This emulates the original mark-1 Continental, popular in its time with the Animals on 'House of the Rising Sun', Doors on 'Light my Fire' and most of their other tracks. Manzarek did use Farfisa later, and even played with the Hammond on their final album, 'LA Woman', but this organ in part defined the 60's sound and is still used by retro bands for that fact. The Damned used it in an early revival where Captain Sensible punched the keyboard wearing gloves to quite good effect. After that The Specials began the Mod/Ska revival using one. The sharp and strong harmonic content has the ability to cut into a mix and make its presence known.

The organ was a british design, eventually sold (to Crumar?) and made into a number of plastic alternatives. Compared to the Hammond this was a fully electronic instrument, no moving parts, and much simpler. It had a very characteristic sound though, sharper and perhaps thinner but was far cheaper than its larger cousin. It used a master oscillator that was divided down to each harmonic for each key (as did the later Hammonds for price reasons). This oscillator division design was used in the first of the polyphonic synthesisers where the divided note was fead through individual envelope generators and a shared or individual filter (Polymoog et al).

The Vox is also a drawbar instrument, but far simplified compared to the Hammond. It has 4 harmonic mixes, 16', 8' and 4' drawbars each with eight positions. The fourth gave a mix of 3rd and 5th. An additional two drawbars controlled the overall volume and waveforms, one for the flute or sine waves and another for the reed or ramp waves. The resulting sound could be soft and warm (flute) or sharp and rich (reed).

There are two switches on the modulator panel, one for vibrato effect and one for memories and options. Options give access to an chorus effect rather than the simple vibrato, but this actually detracts from the qualities of the sound which are otherwise very true to the original.

Sequential Circuits Prophet-5
Sequential Circuits Prophet-52 (the '5' with chorus)

Sequential circuits released amongst the first truly polyphonic synthesisers where a group of voice circuits (5 in this case) were linked to an onboard computer that gave the same parameters to each voice and drove the notes to each voice from the keyboard. The device had some limited memories to allow for real live stage work. The synth was amazingly flexible regaring the oscillator options and modulation routing, producing some of the fattest sounds around. They also had some of the fattest pricing as well, putting it out of reach of all but the select few, something that maintained its mythical status. David Sylvian of Duran Duran used the synth to wide acclaim in the early 80's as did many of the new wave of bands.

The -52 is the same as the -5 with the addition of a chorus for little other reason than it was easy and others have done it on the Win platform.

The design of the Prophet synthesisers follows that of the Mini Moog. It has three oscillators with one dedicated as an LFO. The second audio oscillator can also function as a second LFO, and can cross modulate oscillator A for FM type effects. The audible oscillators have fixed waveforms with pulse width modulation of the square wave. These are then mixed and sent to the filter with two envelopes, for the filter and amplifier.

Modulation bussing is quite rich. There is the wheel modulation which is global, taking the LFO and Noise as a mixed source, and send it under wheel control to any of the oscillator frequency and pulse width, plus the filter cutoff. Poly mods take two sources, the filter envelope and Osc-B output (which are fully polyphonic, or rather, independent per voice), and can route them through to Osc-A frequency and Pulse Width, or through to the filter. To get the filter envelope to actually affect the filter it needs to go through the PolyMod section. Directing the filter envlope to the PW of Osc-A can make wide, breathy scaning effects, and when applied to the frequency can give portamento effects.

LFO

Frequency: 0.1 to 50 Hz
Shape: Ramp/Triangle/Square. All can be selected, none selected should give a sine wave (*)

(*) Not yet implemented.

Wheel Mod:

Mix: LFO/Noise
Dest: Osc-A Freq/Osc-B Freq/Osc-A PW/Osc-B PW/Filter Cutoff

Poly Mod: These are affected by key velocity.

Filter Env: Amount of filter envelope applied Osc-B: Amount of Osc-B applied:
Dest: Osc-A Freq/Osc-A PW/Filter Cutoff

Osc-A:

Freq: 32' to 1' in octave steps
Shape: Ramp or Square
Pulse Width: only when Square is active. Sync: synchronise to Osc-B

Osc-B:

Freq: 32' to 1' in octave steps
Fine: +/- 7 semitones
Shape: Ramp/Triangle/Square
Pulse Width: only when Square is active. LFO: Lowers requency by 'several' octaves. KBD: enable/disable keyboard tracking.

Mixer

Gain for Osc-A, Osc-B, Noise

Filter

Cutoff: cuttof frequency
Res: Resonance/Q/Emphasis
Env: amount of PolyMod affecting to cutoff.

Envelopes: One each for PolyMod (filter) and amplifier.

Attack
Decay
Sustain
Release

Global

Master Volume
A440 - stable sine wave at A440 Hz for tuning. Midi: channel up/down
Release: release all notes
Tune: autotune oscillators.
Glide: amount of portamento

Unison: gang all voices to a single 'fat' monophonic synthesiser.

This is one of the fatter of the Bristol synths and the design of the mods is impressive (not my design, this is as per sequential circuits spec). Some of the cross modulations are noisy, notably 'Osc-B->Freq Osc-A' for square waves as dest and worse as source.

The chorus used by the Prophet-52 is a stereo 'Dimension-D' type effect. The signal is panned from left to right at one rate, and the phasing and depth at a separate rate to generate subtle chorus through to helicopter flanging.

Memories are loaded by selecting the 'Bank' button and typing in a two digit bank number followed by load. Once the bank has been selected then 8 memories from the bank can be loaded by pressing another memory select and pressing load. The display will show free memories (FRE) or programmed (PRG).

Sequential Circuits Prophet-10

The prophet 10 was the troublesome younger brother of the Pro-5. It is almost two Prophet-5 in one box, two keyboards and a layering capability. This model was not a big seller, it was temperamental and liable to be temperature sensative due to the amount of electronics hidden away inside. The original layering and 'unison' allowed the original to function as two independent synths, a pair of layered synths (both keyboards then played the same sound), as a monophonic synth in 'unison' mode on one keybaord with a second polyphonic unit on the other, or even all 10 voices on a single keyed note for a humungous 20 oscillator monophonic monster.

Phil Collins used this synth, and plenty of others who might not admit to it.

The emulator uses the same memories as the Prophet-5, shares the same algorithm, but starts two synths. Each of the two synths can be seen by selecting the U/D (Up/Down) button in the programmer section. Each of the two synthesisers loads one of the Pro-5 memories.

There was an added parameter - the Pan or balance of the selected layer, used to build stereo synths. The lower control panel was extended to select the playing modes:

Dual: Two independent keyboards
Poly: Play note from each layer alternatively Layer: Play each layer simultaneously.

In Poly and Layer mode, each keyboard plays the same sounds.

Mods: Select which of the Mod and Freq wheels control which layers.

Oberheim OB-X

Oberheim was the biggest competitor of Sequencial Circuits, having their OB range neck and neck with each SC comparable. The sound is as fat, the OB-X similar to the Prophet-5 as the OB-Xa to the Prophet-10. The synths were widely used in rock music in the late seventies and early 80s. Their early polyphinic synthesisers had multiple independent voices linked to the keyboard and were beast to program as each voice was configured independently, something that prevented much live usage. The OB-X configured all of the voices with the same parameters and had non-volatile memories for instant recall.

Priced at $6000 upwards, this beast was also sold in limited quantities and as with its competition gained and maintained a massive reputation for rich, fat sounds. Considering that it only had 21 continuous controllers they were used wisely to build its distinctive and flexible sound.

The general design again follows that of the Mini Moog, three oscillators with one dedicated as an LFO the other two audible. Here there is no mixer though, the two audible oscillators feed direclty into the filter and then the aplifier.

The richness of the sound came from the oscillator options and filter, the latter of which is not done justice in the emulator.

Manual

Volume
Auto: autotune the oscillators
Hold: disable note off events
Reset: fast decay to zero for envelopes, disregards release parameter. Master Tune: up/down one semitone both oscillators.

Control

Glide: up to 30 seconds
Oscillator 2 detune: Up/down one semitone

Unison: gang all voices to a single 'fat' monophonic synthesiser.

Modulation

LFO: rate of oscillation
Waveform: Sine/Square/Sample&Hold of noise src. Triangle if none selected.

Depth: Amount of LFO going to:

        Freq Osc-1
        Freq Osc-2
        Filter Cutoff

PWM: Amount of LFO going to:

        PWM Osc-1
        PWM Osc-2

Oscillators

Freq1: 32' to 1' in octave increments. PulseWidth: Width of pulse wave (*). Freq2: 16' to 1' in semitone increments.

Saw: sawtooth waveform Osc-1 (**)
Puls: Pulse waveform Osc-1

XMod: Osc-1 FW to Osc-2 (***)
Sync: Osc-2 sync to Osc-1

Saw: sawtooth waveform Osc-2
Puls: Pulse waveform Osc-2

Although this is a single controller it acts independently on each of the oscillators - the most recent to have its square wave selected will be affected by this parameter allowing each oscillator to have a different pulse width as per the original design.

** If no waveform is selected then a triangle is generated.

*** The original synth had Osc-2 crossmodifying Osc-1, this is not totally feasable with the sync options as they are not mutually exclusive here. Cross modulation is noisy if the source or dest wave is pulse, something that may be fixed in a future release.

Filter

Freq: cutoff frequency
Resonance: emphasis (*)
Mod: Amount of modulation to filter cutoff (**)

Osc-1: Osc-1 to cutoff at full swing. KDB: Keyboard tracking of cutoff.

Half/Full: Oscillator 2 to Cutoff at defined levels (***) Half/Full: Noise to Cutoff at defined levels (***)

In contrast to the original, this filter can self oscillate.

** The original had this parameter for the envelope level only, not the other modifiers. Due to the filter implementation here it affects total depth of the sum of the mods.

*** These are not mutually exclusive. The 'Half' button gives about 1/4, the 'Full' button full, and both on gives 1/2. They could be made mutually exclusive, but the same effect can be generated with a little more flexibity here.

Envelopes: One each for filter and amplifier.

Attack
Decay
Sustain
Release

The oscillators appear rather restricted at first sight, but the parametrics allow for a very rich and cutting sound.

Improvements would be a fatter filter, but this can be argued of all the Bristol synthesisers as they all share the same design. It will be altered in a future release.

The OB-X has its own mod panel (most of the rest share the same frequency and mod controls). Narrow affects the depth of the two controllers, Osc-2 will make frequency only affect Osc-2 rather than both leading to beating, or phasing effects if the oscillators are in sync. Transpose will raise the keyboard by one octave.

Memories are quite simple, the first group of 8 buttons is a bank, the second is for 8 memories in that bank. This is rather restricted for a digital synth but is reasonably true to the original. If you want more than 64 memories let me know.

Oberheim OB-Xa

This is almost two OB-X in a single unit. With one keyboard they could provide the same sounds but with added voicing for split/layers/poly options. The OB-Xa did at least work with all 10 voices, had a single keyboard, and is renound for the sounds of van Halen 'Jump' and Stranglers 'Strange Little Girl'. The sound had the capability to cut through a mix to upstage even the biggest guitar solo's. Oberheim went on to make the most over the top analogue synths before the cut price alternatives and the age of the DX overcame them.

Parameters are the same as the OB-S as the algorithm shares the same code, with a few changes to the mod routing. The main changes will be in the use of Poly/Split/Layer controllers for splitting the keyboard and layering the sounds of the two integrated synthesisers.

The voice controls apply to the layer being viewed, selected from the D/U button.

Manual

Volume
Balance
Auto: autotune the oscillators
Hold: disable note off (*)
Reset: fast decay to zero for envelopes, disregards release parameter. Master Tune: up/down one semitone both oscillators.

Control

Glide: up to 30 seconds
Oscillator 2 detune: Up/down one semitone

Unison: gang all voices to a single 'fat' monophonic synthesiser.

Modulation

LFO: rate of oscillation
Waveform: Sine/Square/Sample&Hold of noise src. Triangle if none selected.

Depth: Amount of LFO going to:

        Freq Osc-1
        Freq Osc-2
        Filter Cutoff

PWM: Amount of LFO going to:

        PWM Osc-1
        PWM Osc-2
        Tremelo

Oscillators

Freq1: 32' to 1' in octave increments. PulseWidth: Width of pulse wave (*). Freq2: 16' to 1' in semitone increments.

Saw: sawtooth waveform Osc-1 (**)
Puls: Pulse waveform Osc-1

Env: Application of Filter env to frequency Sync: Osc-2 sync to Osc-1

Saw: sawtooth waveform Osc-2
Puls: Pulse waveform Osc-2

Although this is a single controller it acts independently on each of the oscillators - the most recent to have its square wave selected will be affected by this parameter allowing each oscillator to have a different pulse width as per the original design.

** If no waveform is selected then a triangle is generated.

Filter

Freq: cutoff frequency
Resonance: emphasis (*)
Mod: Amount of modulation to filter cutoff (**)

Osc-1: Osc-1 to cutoff at full swing. KDB: Keyboard tracking of cutoff.

Half/Full: Oscillator 2 to Cutoff at defined levels (***)

Noise: to Cutoff at defined levels
4 Pole: Select 2 pole or 4 pole filter

In contrast to the original, this filter will self oscillate.

** The original had this parameter for the envelope level only, not the other modifiers. Due to the filter implementation here it affects total depth of the sum of the mods.

Envelopes: One each for filter and amplifier.

Attack
Decay
Sustain
Release

Mode selection:

Poly: play one key from each layer alternatively for 10 voices Split: Split the keyboard. The next keypress specifies split point Layer: Layer each voice on top each other.

D/U: Select upper and lower layers for editing.

Modifier Panel:

Rate: Second LFO frequency
Depth: Second LFO gain
Low: Modifiers will affect the lower layer Up: Modifiers will affect the upper layer Multi: Each voice will implement its own LFO Copy: Copy lower layer to upper layer

Mod 01: Modify Osc-1 in given layer Mod 02: Modify Osc-2 in given layer PW: Moduify Pulse Width
AMT: Amount (ie, depth) of mods and freq wheels

Transpose: Up or Down one octave.

The oscillators appear rather restricted at first sight, but the parametrics allow for a very rich and cutting sound.

Roland Juno-6

Roland was one of the main pacemakers in analogue synthesis, also competing with the Sequential and Oberheim products. They did anticipate the moving market and produced the Juno-6 relatively early. This was one of the first accessible synths, having a reasonbly fat analogue sound without the price card of the monster predecessors. It brought synthesis to the mass market that marked the decline of Sequential Circuits and Oberheim who continued to make their products bigger and fatter. The reduced price tag meant it had a slightly thinner sound, and a chorus was added to extend this, to be a little more comparable.

The synth again follows the Mini Moog design with three oscillators one of which is dedicated to being an LFO, these fead into a filter and then an amplifier. There is only one envelope generator that can apply to both the filter and amplifier.

Control

DCO: Amount of pitch wheel that is applied to the oscillators frequency. VCF: Amount of pitch wheel that is applied to the filter frequency.

Tune: Master tuning of instrument

Glide: length of portamento

LFO: Manual control for start of LFO operation.

Hold: (*)

Transpose: Up/Down one octave
Hold: prevent key off events

LFO

Rate: Frequency of LFO
Delay: Period before LFO is activated Man/Auto: Manual or Automatic cut in of LFO

DCO

LFO: Amount of LFO affecting frequency. Affected by mod wheel. PWM: Amount of LFO affecting PWM. Affected by mod wheel.

ENV/LFO/MANUAL: Modulator for PWM

Waveform: Pulse or Ramp wave. Pulse has PWM capabily.

Sub oscillator:

On/Off first fundamental square wave.

Sub: Mixer for fundamental
Noise: Mixer of white noise source.

HPF: High Pass Filter

Freq

Frequency of cutoff.

VCF

Freq

Cutoff frequency

Res

Resonance/emphasis.

Envelope

+ve/-ve application

Env

Amount of contour applied to cutoff

LFO

Depth of LFO modulation applied.

KBD

Amount of key tracking appliied.

VCA

Env/Gate:

Contour is either gated or modulated by ADSR

Level

Overall volume

ADSR

Attack
Decay
Sustain
Release

Chorus

8 Selectable levels of Dimension-D type helicopter flanger.

The original instrument had a basic sequencer on board for portamento effects on each key. In fact, so did the Prophet-10 and Oberheims. This has not been implemented on any of the synths and is a potential area for development.

The LFO cut in and gain is adjusted by a timer and envelope that it triggers. This currently (0.9) only works when the synth is active on Midi channel 0.

The Juno would improve from the use of the prophet DCO rather than its own one. It would require a second oscillator for the sub frequency, but the prophet DCO can do all the Juno does with better resampling and PWM generation.

Yamaha DX-7

Released in the '80s this synth quickly became the most popular of all time. It was the first fully digital synth, employed a revolutionary frequency modulated algorithm and was priced much lower than the analogue monsters that preceeded it. Philip Glass used it to wide effect for Miami Vice, Prince had it on many of his albums, Howard Jones produced albums filled with its library sounds. The whole of the 80's were loaded with this synth, almost to the point of saturation. There was generally wide use of its library sounds due to the fact that it was nigh on impossible to programme, only having entry buttons and the algorithm itself was not exactly intuitive, but also because the library was exceptional and the voices very playable. The emulation is a 6 operator per voice, and all the parameters are directly accessible to ease programming.

The original DX had six operators although cheaper models were release with just 4 operators and a consequently thinner sound. Each operator is a sine wave oscillator with its own envelope generator for amplification and a few parameters that adjusted its modulators. It used a number of different algorithms where operators were mixed together and then used to adjust the frequency of the next set of operators. The sequence of the operators affected the net harmonics of the overall sound. Each operator has a seven stage envelope - 'ramp' to 'level 1', 'ramp' to 'level 2', 'decay' to 'sustain', and finally 'release' when a key is released. The input gain to the frequency modulation is controllable, the output gain is also adjustable, and the final stage operators can be panned left and right.

Each operator has:

Envelope

        Attack: Ramp rate to L1
        L1: First target gain level
        Attack: Ramp rate from L2 to L2
        L2: Second target gain level
        Decay: Ramp rate to sustain level
        Sustain: Continuous gain level
        Release: Key release ramp rate

Tuning

        Tune: +/- 7 semitones
        Transpose: 32' to 1' in octave increments

        LFO: Low frequency oscillation with no keyboard control

Gain controls:

Touch: Velocity sensitivity of operator.

        In gain: Amount of frequency modulation from input
        Out gain: Output signal level

        IGC: Input gain under Mod control
        OGC: Output gain under Mod control

        Pan: L/R pan of final stage operators.

Global and Algorithms:

24 different operator staging algorithms Pitchwheel: Depth of pitch modifier Glide: Polyphonic portamento
Volume
Tune: Autotune all operators

Memories can be selected with either submitting a 3 digit number on the keypad, or selecting the orange up/down buttons.

An improvement could be more preset memories with different sounds that can then be modified, ie, more library sounds. There are some improvements that could be made to polyphonic mods from key velocity and channel/poly pressure that would not be difficult to implement.

The addition of triangle of other complex waveforms could be a fun development effort (if anyone were to want to do it).

KORG MONOPOLY

A synth suite would not be complete without some example of a Korg instrument, the company was also pivotal in the early synthesiser developments. This is an implementation of their early attempts at polyphonic synthesis, it was either this one or the Poly-6 (which may be implemented later). Other choices would have been the MS series, MS-20, but there are other synth packages that do a better job of emulating the patching flexibility of that synth - Bristol is more for fixed configurations.
As with many of the Korg synths (the 800 worked similarly) this is not really true polyphony, and it is the quirks that make it interesting. The synth has four audio oscillators, each independently configurable but which are bussed into a common filter and envelope pair - these are not per voice but rather per instrument. The unit has different operating modes such that the four oscillators can be driven together for a phat synth, independently for a form of polyphony where each is allocated to a different keypress, and a shared mode where they are assigned in groups depending on the number of keys pressed. For example, if only 2 notes are held then each key is sounded on two different oscillators, one key is sounded on all 4 oscillators, and 3 or more have one each. In addition there are two LFOs for modulation and a basic effects option for beefing up the sounds. To be honest to the original synth, this emulation will only request 4 voices from the engine (one drives each oscillator). Korg is one of the few original manufacturers to have survived the transititon to digital synthesis and are still popular.

One thing that is immediately visible with this synth is that there are a lot of controllers since each oscillator is configured independently. This is in contrast to the true poly synths were one set of controls are given to configure all the oscillators.

The algorithm is still in development, and will continue once the Jack drivers have been finalised.

For the sake of being complete, below is the output from the GUI verbose help text. It gives an overview of the GUI and engine options (well, mostly engine):