The Vox amps manufactured in America during the 1960s were loaded with innovative features. These amps often offered far more than reverb and tremolo. A number included treble and mid range boost switches, fuzz tone, Repeat Percussion and Tone-X. Outboard effects, such as the Wah pedal, were also offered. Vox offered a plethora of ways to modify the amplified tone of an electric guitar.

In 1967, looking for new markets, Thomas Organ entered the band instrument business with their "Vox Ampliphonic" line. Vox introduced a line of 66 woodwind and brass instruments with audio pickups, allowing these instruments to be played through a Vox amplifier. But their goal went beyond amplifying band instruments through an amp. Thomas Organ also wished to develop outboard effects devices that would radically modify the tone of reed and brass band instruments just as MRB, fuzz tone, and Repeat Percussion had done for guitar. Vox developed three signal processing products to accomplish this goal: the pocket sized Octavoice I amd II and the Stereo Multi-Voice.

The 1968 Vox Ampliphonic catalog described the Stereo Multi Voice as follows: "A revolutionay idea in Music! Vox's Stereo-Multi-Voice lets one musician sound like an entire section. Here's how it works: Preset tabs for the octaves and voices that you want. Then with the tap of a foot, change or mix octaves; swing back and forth between different voices. You can make a sax sound like a clarinet or like several musicians playing all at once."

The electronic design of the Stereo Multi-Voice was based on the frequency generation and tonal filtering circuitry used in Thomas home organs. These organs used twelve individual frequency generator circuit cards, one for each note in the scale. Each of these cards had a "master tone oscillator" circuit that generated the highest pitched tones in the organ. The high-pitched signal from each of these master tone oscillators was then fed serially through a number of frequency "divider" network circuits. Each frequency divider network would drop the frequency of the master tone oscillator by one octave. Through the use of five of these serial frequency divider networks in each of the twelve tone generator circuit cards, the pitches needed to complete a five octave organ were derived.

The Vox Stereo Multi-Voice worked on a similar principle. The Stereo Multi-Voice substituted the signal from the audio pickup mounted to a Vox Ampliphonic clarinet or saxophone for the signal created by the "master tone oscillator" in an electronic organ. The audio signal from the clarinet or sax pickup was fed through either a single frequency doubler network to raise the original pitch an octave, or a pair of serial frequency divider networks to drop the original pitch of the instrument by one or two octaves.

By means of an example, the innovative pitch modifying circutry in the Vox Stereo Multi-Voice allowed the amplified signal of a tenor sax to be dropped an octave, now resembling the sound of a baritone sax.

The signals from the divider and doubler networks signals were additionally sent through tonal filtering circuits similar to those utilized in Thomas home organs. The tonal shaping provided by this circuit allowed the Stereo Multi-Voice to emulate the sounds of eight reed and string instruments: soprano sax, violin, cello, alto saxophone, clarinet, tenor saxophone, bass clarinet and Vox bass guitar.

A four button foot switch (shown at left), similar to those supplied with US Vox solid state amps, provided the ability for remote switching of effects. The pedal included an "Instrument" foot switch to enable the modified audio signal, a "Left" and "Right" foot switch to direct the audio output to the right or left channels, and a "V" foot switch that turned on a vibrato effect.

The Stereo Multi-Voice not only worked with amplified woodwind and brass instruments. It also gained favor with guitarists.