Alesis Quadrasynth

Alesis Quadrasynth

(No photo yet. Please contribute one!) Alesis Quadrasynth keyboard Alesis Quadrasynth S4 Module
W × H × D (mm)	1220 × 115 × 355 (keyboard) 482 × 43 × 150 (module)
Rack units	1U, full width (modules only)
Weight	13.6kg (keyboard) ~2kg (module)
Keyboard	76 keys
Manufacturer	Alesis
Release date	1994
Parts	16
Max polyphony	64
Normal presets	Programs: 128 factory + 128 user Mixes: 100 factory + 100 user
Expansion	1 × Alesis PCMCIA
Effects	Variable, see effects.
Alesis Quadrasynth Plus →

The Alesis Quadrasynth and Alesis Quadrasynth S4 are synthesizers released in 1994 by Alesis. They are the first models to incorporate the "QS Composite Synthesis" synthesis to produce sounds. It features a 16 MB Wave ROM, storing high quality uncompressed sounds at 48 kHz.

The keyboard version features 76 keys with velocity and aftertouch and an amber screen, the module version is 1u tall, full width (19") and is rather light, it also features Alesis ADAT inputs and outputs accessible via optical ports. It could have possibly been used to interface with ADAT equipment of the time. This model and the S4 Plus also use the 9V AC 4-pin DIN port for power delivery. For more information, please see our power supplies article.

The name "Quadrasynth" was likely chosen as they have previously used the "Quadra" moniker for their Quadraverb lines of effect units, but also possibly because there are up to four elements that can make a program, and there are four knobs featured on the front panel that lets you modify parameters with ease.

Internally the keyboard seems to be referred to as the S5 - it is similar to the module version (the S4), however it incorporates mechanisms designed for keyboards such as the keybed, bender wheels, aftertouch sensors and more.

For the time it ended up gathering favourable reviews from publications, citing its easy-to-use interface, multitimbrality, expandability and large (for the time) 64-voice polyphony being obvious positives, with the filter being cited as a downside. Uniquely, or perhaps as to be expected with Alesis products of the time, the user interface itself is unconventional - rather than relying on a character display like the U-20 and JV-80, or a fully dot matrix display like the XV-5080 or the Korg M1's, they opted to use a custom LCD that has a dot matrix display for patch names, with the bottom section being entirely dedicated to displaying bespoke elements that can be highlighted.

Picture of Alesis S4 Plus's display in editing mode, showing most of the individual segments as active. Take note that the currently selected menu is underlined.

All the models feature a compliment of MIDI IN/OUT/THRU ports, as well as a digital output, a 48khz clock sync input, 2 pairs of outputs, PCMCIA expansion and a headphone jack. Depending on the model, the power input can be a 3-pin kettle lead type (similar to PC power supplies and other home appliances), or a special 4-pin DIN that delivers 9V AC power.

The keyboard version features in addition to these a complement of sustain and expression pedal inputs, which are missing from the module version as they are irrelevant there.

The Quadrasynth and S4 modules shipped with two built-in demo songs - "Cyberfunk" and "Bach's Bad Dream (with apologies to J.S. Bach's Prelude in Am)", both sequenced by Stephen Kay.

Synthesis

The QS Composite Synthesis standard is used across every Alesis Quadrasynth and QS line of products, it is comprised of 64 total voices, with each note being able to use up to four. This is comparable to the Korg ai² in terms of features, and to the Roland JV-1080 in terms of voice count and the voices-per-note figure.

The filter employed is a non-resonant type similar to the one on the Korg M1 or the Korg 01/W. To compensate for this, on-board waveforms feature multisamples with various resonance levels, which can be assigned to different velocity levels or pitches depending on the patch that is designed.

Each voice has access to an amplitude envelope and LFO, a filter section (with LFO and EG), a pitch modulation section, as well as a modulation matrix specific to that voice. These are then fed to an effects section - four buses are available, but the way these are organised and routed depend on the selected layout.

Effects

All effects information was collected with help from the manuals, as well as emagic's SoundDiver 3.0 software.

Configuration #1 - 4 sends, 1 reverb

4 FX sends are available in this mode - the first three sends each have their own independent pitch unit that controls chorus and/or flanging. Afterwards, each of the 4 sends has their own delays, which can have their own independent delay and feedback time. These can all be routed to the singular reverb unit in this mode, if desired. The pitch mode can all be changed independently, but only the first two delay instances can be changed, while the latter 2 are locked to "Mono Delay"

Configuration #2 - 4 sends, 2 reverbs

4 FX sends are available in this mode, but only the first send has a delay unit, which is hard-set to Mono Delay. Two pitch units exist, one on FX send 1 and one on FX send 3, with only the first one being modifiable from "Mono Chorus". FX1 & 2 get summed up towards Reverb 1, and FX3 & 4 get summed up towards Reverb 2, both which are fully configurable.

Configuration #3 - 4 sends, 1 lezlie (sic)

4 FX sends are available in this mode - it is set up similarly to Configuration #1, however the first pitch unit is replaced with a Leslie simulation.

Configuration #4 - 2 sends, with EQ

2 FX sends are avaliable in this mode - each going through one pitch unit, and then one delay unit - fully modifiable. Both get summed up into a reverb, which is also fully modifiable, which then gets output to a 2-band shelving EQ.

Behind The Scenes

According to an interview with Marcus Ryle, one of the designers behind the Quadrasynth architecture, he stated he had wanted to create a synthesizer that is simple to understand and edit, but can be quite complex. In the article, it's also noted that the reason filters are non-resonant was to achieve a higher polyphony count of 64 voices, and that the design philosophy was largely inspired by the team's prior work on various Oberheim products, like the Oberheim Matrix synths, and who have also worked on the SampleCell format.

It is easy to see some of these aspects in the final product: The bespoke LCD that makes editing easier than it would be on a 2-line unit, the quad knobs that allow for easy sound manipulation, or the variety of modulation options - all cited as points the team wanted to achieve with their design. Even the design of the Alesis S4 module bears some resemblence to the Oberheim Matrix 1000.

Much like how they reused technology from their effects unit of the time, Alesis would also end up using many of the sounds they recorded and produced for their drum machine lines of products (like the Alesis D4) as a basis for the kits available on the Quadrasynth.

Terminology

The Quadrasynth line divide their sounds into three different types:

• Mixes, which comprise of multiple programs playing concurrently, similar to Combi mode on Korg synthesizers or Performance mode on Roland products.
• Programs, which can comprise of up to four different voices. This is similar to the Prog mode on Korg synths, and the Patch mode on Roland products.
• Voices, which can be assigned a waveform, envelopes, filter cutoff, and so on. Similar to what a "Tone" is on Roland products.

Oddities

• Using CC#0, also known as Bank change MSB will not change the bank between the user bank and the factory bank. This is fixed for the plus models.
• You could upgrade from the original model to the plus model via a slot-in card inside the unit, which was way cheaper compared to buying a new synth. This was labeled as a v2.0 upgrade in some publications, as well as in the Plus manuals.
• While the officially released expansion cards will work with any Quadrasynth or QS unit, on these original models you need to copy the card contents into the user memory, wiping out any custom patches or mixes one may have made. This is not the case with any of the later units.
• While PCMCIA cards were common back then, only specific cards will work with Alesis synths - it requires a specific generation of Linear Flash memory. Normally these synths can only read up to 8 megabits, although with mods it may be able to read beyond that. For more information please check the Alesis PCMCIA article.
• Alesis devices of the time employed the use of BR2325 batteries. If replacing a battery, one can instead solder a CR2032 battery holder in its place and use a CR2032 battery inside with no issues. For more information please consult the replacing backup batteries article.
• Although rare, the Quadrasynth can display quasi-error codes. For example, if there is no battery detected (or if the battery failed), it would not boot up, instead displaying a screen with all segments turned on, except the indicators for MIDI channels 1-5 and the MIX program number would read "_3".