The Yamaha SPX900 Professional Multi-effect Processor marked a major leap forward in digital effects technology when it was introduced in the late 1980s. Designed for both studio and live sound applications, the Yamaha SPX900 delivered a wide range of high-quality digital effects with full programmability, MIDI control, external control support and deep parameter editing. Building on the success of its predecessor, the Yamaha SPX90, this unit became a go-to tool for engineers and musicians who required versatility, reliability and sonic precision in a compact format.
Central to the Yamaha SPX900’s performance was Yamaha’s second-generation LSI digital signal processing technology. This allowed for a full complement of reverberation effects, including highly detailed early reflections, sophisticated modulation programs, dynamic pitch-shifting, compression, 2D panning, distortion, and more. Among its most powerful features was the multi-effect capability, which enabled up to five different effects to be used simultaneously in both series and parallel configurations. This gave users the power of multiple dedicated processors within a single 1U rackmount chassis.
The Yamaha SPX900 operated at a sampling frequency of 44.1kHz and utilised 16-bit A/D and D/A conversion, delivering a frequency response of 20Hz to 20kHz and a typical dynamic range of 90dB. The effects library included 50 factory programs, ranging from natural room and hall reverbs to complex multi-effect chains. Users could store an additional 49 custom programs in the onboard RAM, allowing complete control over sound design and recall in performance or production settings.
The Yamaha SPX900 divided parameters into four groups for extensive editing. These included “main” parameters that shaped the character of the selected effect, additional effect-specific parameters, and dynamic EQ and filter settings. The fourth group offered control over general functions such as input and output level, and effect balance. Effects could be customised in real-time, either manually or using external controllers.
One standout function was the EXTERNAL CONTROL ASSIGN, which allowed users to assign up to two effect parameters from each program to external controllers. This enabled real-time manipulation of effects such as stereo flange speed and depth via foot pedals or rotary dials, with the selected parameters reacting dynamically during a performance. Additionally, MIDI implementation provided program selection, real-time control of two parameters per program, and full parameter dump and load capabilities for data backup and automation.
An optional remote control unit, the Yamaha RCX1, further enhanced usability. It provided a 16-character by 2-line LCD display and a data entry dial, giving users hands-on access to Yamaha SPX900 functions from a distance of up to 5 metres. The RCX1 allowed fast navigation and parameter editing, particularly valuable in installations or live environments where the processor was not easily accessible.
The effects themselves were wide-ranging and meticulously crafted. Reverb algorithms covered all the expected variations, including halls, plates, rooms and white rooms, with more creative options like tunnel, canyon and basement spaces for dramatic spatial simulation. The reverbs included a programmable gate, allowing reverb tails to be shaped or reversed and triggered via MIDI or footswitch.
Early reflection algorithms included dedicated programs such as percussion early reflections and gate reverb, as well as programmable configurations with up to 19 individual delay taps. These could be tailored for depth, timing and stereo placement, giving engineers a powerful tool for space simulation without using full reverberation.
Delay and echo programs offered independently variable control of left, right and centre channel delays. The stereo echo program supported multi-tap delay creation with precision timing and level control, ideal for rhythmic or spatial delay effects.
Modulation effects included stereo flange, chorus, tremolo, symphonic chorus and phasing. The stereo flange and chorus programs thickened the signal and widened the stereo field, while tremolo added rhythmic amplitude modulation. The symphonic effect created a multi-voice chorus that was particularly effective for enhancing keyboards and vocals.
Pitch-shifting was one of the Yamaha SPX900’s most advanced capabilities. Pitch Change 1 allowed two independently shifted notes in addition to the direct signal, creating complex three-note harmonies. Pitch Change 2 provided two pitch-shifted outputs panned left and right. Pitch Change 3 added a third shifted voice, while Mono Pitch offered single-note shifting for applications like tuning correction or doubling.
The unit also included a unique FREEZE program, allowing up to 1.35 seconds of digital sampling and playback. Captured sound could be looped or triggered once, opening creative avenues for sound design and performance. The PAN and TRIGGERED PAN programs allowed stereo and rotary-style panning, sweeping sound across the stereo field or automating left-right motion based on trigger signals.
Additional programs included compression and distortion. The COMPRESSOR program reduced dynamic range, smoothed out signal fluctuations and included a downward expander for real-time noise reduction. The DISTORTION program emulated guitar amp-style overdrive, with EQ shaping for tonal control. The AURAL EXCITER program added harmonic content to brighten and enhance the presence of the input signal, often used to lift buried elements in a mix without increasing level.
The Yamaha SPX900 also offered a NOISE GATE program for gating unwanted signal content, with adjustable threshold and timing. Reverse gate effects were also possible, gradually increasing signal after a trigger.
Multi-effects were a major strength of the Yamaha SPX900. A total of ten MULTI programs offered combinations of chorus, echo, reverb, compressor, distortion, EQ and Exciter, with parameter control over each effect in the chain. For added flexibility, DUAL EFFECT programs gave independent processing to left and right channels. For example, one channel could run plate reverb while the other ran echo, enabling complex stereo configurations.
Physically, the Yamaha SPX900 measured 480mm x 45.2mm x 319mm and weighed 4.4kg. It had unbalanced 6.3mm jack inputs and outputs, with switchable input and output levels between +4dBm and -20dBm. A rotary level control allowed easy adjustment of input gain. The front panel featured a 16-character LCD, a level meter, and control keys for program recall, editing, and parameter assignment. The rear panel housed MIDI In, Out and Thru, memory in/out, trigger, footswitch, and bypass connectors. The system supported full MIDI program change, control change, bulk dump, and parameter dump functions.
In both studio and live environments, the Yamaha SPX900 stood out as one of the most complete and forward-thinking effects processors of its time. Its balance of pristine audio quality, deep programmability and real-time control earned it a permanent place in professional racks worldwide.
