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Kurzweil K2500R

Rack Sound Module By Paul Ward
Published October 1995

Offering evolution not revolution, the feature‑laden K2500R packs one heck of a sonic punch. Paul Ward remains impressed...

As a committed K2000 user I have waited with some anticipation for the next generation of Kurzweil synthesizers to roll off the production line. Given the K2000's reputation for quality, power and ease of use, it is fascinating to contemplate how Kurzweil will attempt to better it. In last month's preview I mentioned that, on the face of it, the K2500 series essentially represents a bigger and, potentially, better K2000 rather than any fundamentally new technology. Now, with a few weeks of solid use under my belt, I can confirm that my first impressions were accurate. With this in mind, I'll often make comparisons between the two instruments during the course of this review. Therefore I'd recommend any interested parties not already familiar with the K2000 series to get hold of SOS March 1992, wherein the K2000 was first reviewed.

Confidence Building

The K2500R comes in a weighty, 3U rackmounting package, exhibiting the kind of build quality that immediately inspires confidence. On the rear panel are a host of sockets to make meaningful contact with the outside world. In addition to the main stereo mix sockets, Kurzweil have blessed the K2500R with a healthy array of eight separate outputs, configurable as four stereo pairs if desired. Each of these sockets can also be used as an insert point to provide extra processing before sounds arrive at the main mix outputs. A pair of digital audio outputs are available from either the XLR electrical AES/EBU or the optical I/O connectors. The ubiquitous trio of In/Out/Thru MIDI sockets is present, although Kurzweil have added a useful feature where the Thru port can also double up as a second MIDI Out, if required — although this will only produce a copy of the data appearing at the normal MIDI output. Two SCSI ports are provided for connection to external disks, CD‑ROM drives, or a computer. The K2500R also implements the new SMDI (SCSI Musical Data Interchange) sample transfer format for vastly increased data transfer rates between compatible machines.

Since the review model came with the sampling option installed, several other connectors were present, including digital inputs of both the optical (on the front panel) and electrical (rear panel) kind, and front panel mounted analogue inputs in the form of a pair of low impedance XLR mic connectors and a high impedance stereo quarter‑inch jack socket. I found this single stereo jack frustrating. Since most stereo sources will usually sport a pair of jack or phono connectors, the use of a special adaptor is required — and these adaptors are the first thing to go missing when you need them most!

The front panel is largely dominated by the 240 x 64 pixel backlit LCD. The display is clearer and brighter than any other that I've come across to date — in fact, the K2500R's display is so powerfully bright that I wanted to dim it a little after a while!

Beneath this display are six 'soft' keys, whose operation is determined by the functions displayed just above them on the currently selected screen. To the left and right of these are the Edit and Exit buttons. I wish these were more clearly marked, speaking from much bitter experience! Just below the soft keys are the eight mode buttons that provide the most basic navigation around the K2500's internals. These give access to Program, Setup, Quick Access, Effects, MIDI, Master, Song, and Disk modes (see 'Operational Modes' sidebar for further details).

To the left of the display is a pair of up/down buttons for scrolling through program layers, MIDI channels, or Quick Access banks. To the right of the display we find the four cursor control buttons, an alpha wheel, a pair of incremental up/down buttons, and a numeric 'telephone style' keypad with Enter and Cancel keys. The front panel is completed by a headphone socket, volume control, and the MS‑DOS compatible (other manufacturers please take note!) high density disk drive. An internal hard drive to a maximum capacity of 1 Gigabyte can be accommodated, which improves slightly on the K2000's maximum size of 760Mb.

New ROM Soundset

Kurzweil have provided a new ROM soundset of 200 programs and 100 setups for the K2500R, including a whole new collection of drum samples. The arrangement of the programs follows a much more logical pattern than those in the K2000, with groups such as pianos, strings, drums, etc located in contiguous program slots. Even allowing for the use of Quick Access banks, this makes the selection of programs much easier and quicker, meaning less time spent using the search functions and more time making music — no bad thing.

The K2500R's base ROM of 8Mb holds a delightful collection of 16‑bit samples, including the usual complement of pianos, strings, brass, voices, 'traditional' sawtooth and square waves, and some more esoteric types such as formants, harmonic partials, and FM transients. Kurzweil's reputation for high quality samples is certainly upheld here, being essentially the same as those in the K2000 (some have been tweaked slightly), with the notable exception of the new set of drum samples. Optional ROM SoundBlocks can take the K2500R up to a maximum of 28Mb of onboard ROM samples (the K2000 is restricted to 24Mb), including the Contemporary and Orchestral blocks and a new 4Mb Stereo Grand Piano.

One of the things that made the K2000 so special was the ability to load samples into RAM (up to 64Mb) and feed them into the powerful VAST (Variable Architecture Synthesis Technology) synthesis engine in exactly the same way as if they were onboard ROM objects. Eight SIMMs sockets allow up to 128Mb of sample RAM to be added to the K2500R, in the form of Macintosh‑type 30‑pin SIMMs. There is no need to buy the sampling option to make use of this feature, which should certainly be of interest to anyone who either already owns a sampler, or merely wants to access third‑party sample libraries. The ability to access Roland, Akai, and Ensoniq sample libraries, as well as reading AIFF and WAV sample files, gives the K2500R access to a potentially huge sound library.

Sampling Option

With the SMP2‑R sampling option fitted I was able to put the K2500R through its own acquisitional paces. Sampling is simple, quick and rewarding here, with plenty of digital and analogue recording options, including sampling of the K2500R's own output. Sampling can be set to begin as soon as a button is pressed or when the input level reaches a predetermined threshold. One of the friendliest features is the display of the number of clipped signal peaks following a recording, which is a useful aid for getting the sampling level as hot as possible before distortion becomes a problem.

Once safely captured, there are a myriad of processing options available to manipulate the samples, including normalisation, pitch shifting and volume ramping, alongside the more conventional looping and truncation functions. As to sampling quality — what goes in comes out — 'nuff said.

Vive LA Difference!

User programs, keymaps, and song data are all held in battery‑backed RAM, which is expandable from the basic 240Kb to 1.25Mb (in the K2000 this was limited to 760Kb) by way of the optional memory upgrade kit.

The K2500R remains compatible with existing K2000 libraries, although changes in some keymaps and the new drum samples may necessitate the use of Kurzweil's 'K2000‑compatibility' diskettes. Once I'd loaded the compatibility files into the K2500R I was able to load in all my old K2000 banks with no trouble at all. Phew!

The sound remains warm and powerful (rather like having your brain hugged through your ears), leaving me in no doubt that, when it comes to sample‑based synthesis, Kurzweil are still up there leading the field.

For all practical purposes, there are few operational differences between the K2500R and a K2000 with version 3 software installed. The extra 48 notes of polyphony will obviously make a large contribution to the size and complexity of arrangements that the K2500R can handle. Additionally, the K2500R can now simultaneously handle up to eight drum programs. For anyone who has experience of a K2000 the significance of this will not go unnoticed, but for other readers I will explain...

Each 'normal' (non‑drum) program in the K2000/K2500R can have up to three 'layers', each of which contains a keymap (which is basically a collection of samples spread across a number of keys). A layer is processed by one of the 31 possible algorithms, consisting of up to five DSP (Digital Signal Processing) functions such as filtering, EQ, distortion, etc. A 'drum' program, however, may contain up to 32 layers, allowing for the selective treatment of 32 different voices. More importantly, these 32 layers do not necessarily have to consist of actual drum sounds. This provides the potential of some truly enormous layered programs for pads, lead, bass, or gargantuan sound effects.

Obviously, these monster programs require more processing power to produce than a simple 3‑layer program, so the older K2000's 68000 CPU limited the user to only one such drum program at a time. A parameter on the 'Master' page defines which MIDI channel will have the privilege of accessing these programs. The K2500R, with its more powerful 68340 CPU, always allows MIDI channels 1‑7 to make use of drum programs, with the 'Master' page parameter now allowing the user to define an eighth channel. Even with an available polyphony of 48 notes, it is unlikely that you are going to get much joy by making each of your programs a 32‑layer behemoth, but you are less likely to see those annoying brackets around a program name (meaning that the current MIDI channel cannot use it). Certainly, a couple of 4‑ or 5‑layer string pads is now no longer taboo.

Apart from this, there are few major surprises in the K2500R's operating system. This doesn't trouble me at all. I think that Kurzweil pretty much got things right from the start of the K2000's life and the process of software upgrades has refined things to a point where few major gripes can still exist. Also, I must say it is still a pleasure to see frequencies calibrated in Hertz and amplitudes in Decibels, rather than the 'finger‑in‑the‑air' 1‑99 settings prevalent on other manufacturer's offerings. True, some of the DSP concepts may take some time to grasp, but programs can be as simple or complex as you feel comfortable with, and the friendly navigation features do a sterling job of helping you through it all.

The K2500R's operating system is held in Flash ROM. In practice, this means that software upgrades are made much easier. Rather than having to perform major open‑heart surgery on the machine to fit new chips, an upgrade can be effected from floppy disk. Kurzweil are making software releases available from an on‑line communications service and this (together with the fact that Kurzweil have made their floppy disks MS‑DOS compatible) should make upgrading about as easy as current technology will allow.

Global Effects

I must admit to being disappointed that Kurzweil have not taken the opportunity to improve upon the K2000's effects handling capabilities. As with most workstations, effects are applied globally, which is often undesirable for a multitimbral arrangement. Some manufacturers offset such problems by offering the ability to apply varying amounts of effect to each program within a multitimbral setup (like, for instance, Korg's Wavestation). Unfortunately, the K2500R either applies the amount of effect globally set for all audio assigned to the group A outputs, or no effects at all by assigning to another output group. This inflexibility will remain one of my main gripes with an otherwise excellent implementation of a multitimbral environment.

Also, with many of today's workstations and synths offering two discrete effects processors, the K2500R's complement of a single multi‑effects processor 'hard‑wired' across the mix outputs seems rather limited in comparison. Help is at at hand, however, in the form of the optional KDFX 4‑stereo‑buss effects board, but not without the extra cost involved.

The effects themselves (courtesy of the Digitech 256 effects chip) are of excellent sonic quality. I have heard complaints that some find the effects in the K2000 to be noisy, but I feel this is probably more down to poor gain management than the processor itself. For myself, I have few complaints about the quality or quantity of effects on offer, both on the original K2000 or here. Kurzweil, to their credit, have made significant changes to the effects patches held in the K2500's ROM to improve the output levels and allay any further criticism.

For the future, Kurzweil are promising several optional upgrades, including the aforementioned KDFX effects board with direct digital output and digital stereo insert, and an 8‑channel interface to AES, ADAT, and DA88 data formats. Keyboard versions of the K2500 are also planned with an intriguing 3‑zone ribbon controller, reminiscent of the old Yamaha CS80. All tantalising prospects, so watch this space.


If I was to tell you about all the other nice features in the K2500R's armoury (such as the object management system, macro files, sample auditioning, and graphic mixer pages) I could probably have this article serialised in a Sunday magazine for the next three months. As it is, I'll just say that if you like what you've read so far, then you'll love the rest.

If you were impressed with Kurzweil's previous offerings, then you are unlikely to be disappointed by the K2500R. We are seeing evolution, not revolution, here in a product that enhances the K2000's winning formula with a little more muscle from the 48‑note polyphony and a little more flexibility from the eight drum channels. The sound remains warm and powerful (rather like having your brain hugged through your ears), leaving me in no doubt that, when it comes to sample‑based synthesis, Kurzweil are still up there leading the field.

The K2500R is not cheap, but neither does it deliver a cheap performance. If push came to shove, I could manage quite happily with a decent mother keyboard and this device alone. I certainly know of one other musician who borrowed this K2500R for a couple of nights and would now be quite prepared to have it replace his entire multi‑synth rig! With the addition of a couple of decent effects processors, I doubt that anyone would realise that all the sounds were emanating from a single machine. For a workstation, this is probably the greatest accolade anyone can give at the moment. If you do have other synths and sound sources in your setup, then don't forget that the K2500R's separate outputs can all be used as external inputs, effectively giving you an 8‑channel mixer into the bargain.

One nagging doubt remains, however. With machines now capable of 128‑note polyphony and physical modelling technology beginning to filter down to a more affordable level, it is uncertain whether the enhancements within the K2500R will be sufficient to excite a market place that is perhaps looking for more far‑reaching innovation. Only time will tell.

Operational Modes

  • PROGRAM mode is likely to be where the K2500R will spend most of its working life. Here you can select the current program for any of the 16 MIDI channels.
  • SETUP mode allows three programs to be layered on any three MIDI channels. This is useful for performance, for instance, when you might need more than one program split across the keyboard.
  • QUICK ACCESS mode provides a method of grouping programs or setups in blocks of 10, for easy instant selection from the numeric keypad. These groupings may, for example, be by song or by type, such as 'Bells' or 'Analogue', with each Quick Access bank capable of being named accordingly.
  • EFFECTS mode is, predictably enough, where the effects processor can be manipulated, perhaps to lock the effect to prevent its changing with the currently selected program.
  • MIDI mode is where the K2500 is told how to handle both received and transmitted MIDI data, perhaps to filter out pitch bend or program messages, for instance. Several options can be set for each individual MIDI channel, such as its audio output or whether it will respond to MIDI program change messages.
  • MASTER mode defines those parameters that affect the machine as a whole, such as global tuning and intonation.
  • SONG mode gives access to the K2500's sequencer.
  • DISK mode is where the loading, saving, deleting and other manipulation of disk objects is performed.

The mode buttons also double up as selector buttons for edit functions, such as layer muting or skipping between marked pages.

32‑Track Sequencer

The K2500R's 32‑track sequencer remains one of the best I have seen on a workstation. All the cutting, copying, quantising, and bouncing functions that you could ever hope for are there in abundance, even down to an event editing screen. The sequencer will drive external synths, with a 'soft‑thru' re‑channelise feature giving painless access to these synths without having to change channels on a mother keyboard. Chunks of sequences can be triggered from a keyboard with the corresponding pitch and velocity changes transposed onto the sequence as it plays. Any track can be defined as a 'drum' track to prevent its contents being transposed. All in all, the sequencer is a truly inspirational tool for jamming, either alone or with a few friends — and it's FUN, which definitely gets my vote every time!

For more serious use I would be unlikely to choose this sequencer in preference to a software‑based package with a mouse and large display, but neither would I be averse to using it in a situation where access to a computer would be problematical. In any case, Standard MIDI Files can be both read and written in Type 0 format, so swapping work between computer and K2500R is a viable proposition.

Favourite K2500R Patches

If you get the chance to check out a K2500R, then the following sounds should bring some instant
aural gratification:

  • 1 Acoustic Piano — still one of the best, in my opinion.
  • 69 Marimba/70 Excited Marimba — show how subtle use of the DSP engine can transform a basic sound.
  • 79 Moogy Bass 2 — Mod wheel and Data slider vary cutoff and resonance. As close to an 'authentic' analogue sound as any sample‑based synth has come.
  • 87 Strummer Guitar — frighteningly realistic acoustic guitar.
  • 97 Gospel Organ — warm and gutsy. Mod wheel speeds up rotary speaker effect.

And while you're at it, flip into Setup mode and try out 58 Swing Trio — I could play around with this one all night!


  • Very powerful workstation/production capabilities in a small package.
  • High quality sound.
  • Expandability.
  • Ease of software upgrades.
  • Slick operating system.
  • Compatibility with a wide range of sample formats.


  • Use of the sequencer can involve a lot of twiddly button‑pushing.
  • Limited assignment of global effects for multitimbral use.


This is a quality workstation with a friendly user interface, eminently capable of sounds and arrangements of epic proportions. If you don't feel a burning need for the extra polyphony, the additional drum channels, the higher level of hardware expandability, or those new drum samples, then you might find the older K2000 a less expensive alternative. With Kurzweil's track record of regular, worthwhile software updates, however, the ease and simplicity of upgrading from disk must also be taken into account. Highly recommended, if your overdraft can run to it.