The E-mu E4X Turbo builds upon the original EIV with 128 voices, expandable RAM up to 128Mb (16Mb standard), an integrated 18-bit effects board, and a 1Gb hard drive of preloaded sounds. The standard E4X comes with 64 voices but is expandable to 128. The updated motherboard features two 72-pin SIMM slots for RAM and two ROM slots for Sound and Flash ROM expansion options.
Memory expansion is more complex than the EIV, accepting only 4Mb, 16Mb, or 64Mb SIMMs. When using different-sized SIMMs, the machine only recognizes half the smaller SIMM's memory, creating somewhat convoluted memory configurations.
The digital I/O includes AES/EBU interface with software-switchable S/PDIF compatibility. While an ADAT optical interface was planned, it hasn't been implemented yet, though it remains a possibility for future development.
The system now features 21 filter types, including four new Z-plane filters that combine EQ precision with formant filtering movement. These new additions - Dual EQ Morph, 2EQ+Lowpass Morph, 2EQ Morph+Expression, and Peak/Shelf Morph - provide unprecedented tonal control. The sound quality combines remarkable clarity with warmth and character. Five new distortion effects have been added to Preset Effects bank B, ideal for heavy metal sounds.
SCSI compatibility has improved significantly, now supporting both Roland S700 and Akai S1000/S1100 formats. While some stereo sounds may not pan correctly, the overall functionality is impressive. CD-ROM compatibility has also improved, with better Mac integration through the 'Mac on SCSI bus' parameter.
The EOS Version 3.0 upgrade added some important features:
- 48-track workstation/sequencer
- Advanced MIDI controller functions
- Computer-based preset editing
- Sound ROM support
- Sample Flash memory support
The cheaper e6400 model offers expandability similar to the E4X Turbo, with options for the 64-voice board, 18-bit effects board, and second MIDI input board. The E4X includes standard features that are optional on the e6400, such as the hard drive, AES/EBU digital interface, and ASCII keyboard connection.
Key advantages include the extensive onboard sound library, ROM expansion capability, new operating system, enhanced filters, and improved compatibility. The main drawbacks are the complicated RAM expansion process and lack of optical digital interface options. Overall, the E4X Turbo represents a significant advancement in professional sampling capabilities, with the added benefit that lesser models can now be upgraded to match its specifications.