Roland's top of the line Super JD synthesizer module, the JD-990's voice architecture includes "analog-like" parameters such as ring modulation, Frequency Cross Modulation (FXM) and oscillator sync. The JD-990 also incorporates D50 like 'structures' and can use any expansion boards or PCM cards created for the JV80 or JD800.

Additional features include

• 6MB or ROM waveform data (expandable to 16MB)
• 24 voice polyphony and 8 part multitimbral capability
• 320x80 dot backlit LCD display
• 8 outputs configured as four stereo pairs
• and 2 space rack mount design.

An on-board multiple effects processor can be used in both single or multi-timbral modes. A special super synth part can use up to 8 effects simultaneously, while other parts can use reverb, chorus and delay.