Why string synths?

Keyboard players have, since the very earliest pipe organs, sought to emulate the sounds of other instruments. Some, like flutes, are easy - what is a pipe organ but a big pile of flutes? Others, like the rich sound of a string section, have proved very difficult indeed. Despite clever voicing and combinations of pipes, it always sounded like an organ, really. This would change in 1963 when two chaps in a workshop in Birmingham created the Mellotron - a fabulous instrument involving miles of quarter-inch tape, tape heads, bicycle chains, felt pads, piano keys, little rubber rollers and not quite enough steel to stop it going out of shape when lifted. For the first time the keyboard player had the sounds of a real string orchestra at his fingertips. The Mellotron was great. It also cost as much as a Rolls-Royce, weighed about the same, but wasn't as reliable. It needed four large roadies to lift it to ensure it was kept entirely straight, otherwise the tape frame would bend and you'd have a wooden box full of brown spaghetti to deal with.

By the 1970s, electronic organs and pianos had taken off to an extent such that the chips needed to make them were cheap as, well, chips, I suppose. Take a high-frequency clock, pass it through a top-octave divider and you've got 11 notes. Pass each of these through an octave divider (divide by two for each octave down) and you've got an organ's worth of square waves waiting to be filtered, keyed and pumped through a speaker. Some bright spark realised that by passing the square waves through a lot of rather specific filters, you got a passable sawtooth waveform - rather like what we need for a string sound. Add that with the bucket-brigade delay lines that were becoming available, and you've got a sweet chorus effect. Simple when you know how. Considering the basis was chips designed for electronic pianos and organs, it's not terribly surprising that many organ manufacturers also produced string ensembles, like the Elka Rhapsody, Crumar Stringman and Hohner String Performer. And, of course, the Dutch manufacturer Eminent. They claim they produced the first electronic organ in 1960, and they're still around making multi-megawatt electronic pipe organ simulations. Their website doesn't even mention their most famous product at all.

Of the many different string ensembles produced, probably the best known (and best sounding) is the ARP Solina, originally produced by Eminent. Some used complicated systems involving multiple oscillators and dividers, but the Solina just had one. The lush chorusing came from an effect unit that used two LFOs and three BBD devices to provide a rich, complex texture from the filtered sawtooth waveforms.

Where you've heard it

Well Jean-Michel Jarre, for a start. He loved his Solina-through-a-phaser thing. Air use one a lot, and it's particularly apparent on "Kelly Watch the Stars".

The plugin

You can download a source tarball, some demos, and a link to the Subversion repository on the download page.

Todo list

The GUI doesn't work at all

The voices guzzle CPU

  • goes from 6% to 14% with all voices sounding
  • slowly goes back down as the voices decay out

The ensemble guzzles CPU

  • with the ensemble using six sin() calls, CPU usage sits at 6.8% according to qjackctl


  • Removing the minblep stops the ticky noise
  • The blep is written into the table but the filter code takes no notice of it
  • There needs to be a buffer for each voice so the oscillator can have the blep kept across frames and run the filter seperately