The Additive synthesizer
Once upon a time, 'additive synthesis' was an expensive and little used option on expensive computer music systems. Now, thanks to Kawai's latest keyboard, there is an instrument dedicated to this type of synthesis. Paul Wiffen, long-time advocate of creating your own waveforms, investigates.
Once upon a time, 'additive synthesis' was an expensive and little used option on expensive computer music systems. Now, thanks to Kawai's latest keyboard, there is an instrument dedicated to this type of synthesis. Paul Wiffen, longtime advocate of creating your own waveforms, investigates.
It is a sad but true fact that these days, more than any revolutionary sound creation process, any new synthesizer needs one great sound that grabs the listener's ears and convinces them to give it a closer examination. Generally speaking, the modern buyer is more interested in hearing factory presets than he is in finding out about an instrument's features and parameters or even (heaven forbid!) trying them out for himself.
Thus it is that 'Digital Native Dance' has sold more D50s than has the concept of Linear Arithmetic synthesis, just as 'E. Piano 1' sold more DX7s than FM. So it is that when the Kawai K5 is demonstrated in stores throughout the land, the fact that additive synthesis is probably the most flexible and refinable method of creating sounds will cut little ice with the average player. He's more interested in hearing that one sound that tells him whether he could walk straight on stage or into the studio with it and grab someone's attention. So the question I've probably raised in everybody's mind now is, does the K5 have such a sound?
Fortunately (as everyone at Kawai will be pleased to hear), it does. It's called 'Big Time', and for those of you whose job it is to sell such machines it's number 3 in Bank 1 of the Multi-Patches (I know it's a cheap way to sell such a versatile instrument as an additive synthesizer but "the public gets what the public wants"). 'Big Time' is probably the best brass sound I've ever heard from a synth (or many a sampler), being actually more reminiscent of the brass section on 'Sledgehammer' than on 'Big Time'. (Well, they're both tracks on Peter Gabriel's So album, aren't they? That's close enough for rock 'n' roll!). And it's streets ahead of any additive sound I've ever heard from a Fairlight, Synclavier or PPG.
Unlike all previous implementations of additive synthesis (except the OSCar, which was monophonic and therefore not universally acceptable as a main keyboard), the Kawai K5 allows you to hear all changes to the harmonic structure as you make them. This real-time edit facility greatly simplifies the process of making your own sounds, as you don't need to select 'Compute' and then wait for the edited waveform to be recalculated before you can hear what you've got.
The second advantage of this realtime implementation is that automatic control of the harmonic content by envelopes and performance parameters like velocity, wheels and pedals, give the expressive control we are now used to in other forms of synthesis (FM, analogue-based, PD, LA, etc). This really is a first on the K5, for although on the OSCar you could hear waveforms change as you were building them, once you had created your waveform you had to use analogue filters to change the harmonic content in real time. On the K5, however, you can directly control the volume levels of different groups of harmonics with independent envelopes. Kawai have also provided low-pass filtering as well, for those synthesists (like me) for whom old habits die hard.
For those of you not familiar with the principles of additive synthesis, it is based on the fact that any complex waveform can, theoretically, be broken down into a series of sine wave oscillations at different frequencies (pitches) and amplitudes (volumes). Now in 'pitched' sounds, ie. musical tones, these frequencies form a mathematically-related series. The lowest frequency, the one we actually perceive as the pitch (usually because it is the loudest) is referred to as the fundamental or first harmonic. The frequency of all the other harmonics will then normally be multiples of the fundamental.
An additive synthesizer allows you to combine a series of individual sine waves already arranged in the correct ratios to the fundamental. So, if you have a fundamental frequency of 100Hz, the third harmonic will have a frequency three times that of the fundamental (ie. 300Hz), the seventh harmonic will be seven times the fundamental (ie. 700Hz) and so on. By altering the levels of these harmonics you can change the timbre (tone) of the sound. And by doing this in real time, ie. as the note sounds, you can cause the timbre to change as a note is being played, which is what happens in the majority of acoustic instrument timbres. This is why the K5 gives you the most useful way of making sounds using additive methods, with the ability to vary the level of different harmonics in real time.
However, the major drawback there has always been with additive synthesis is the amount of time it can take to set the different levels of all the harmonics, especially when you are looking at 63 harmonics, which is how many the K5 offers (if this isn't enough you can assign a second sound source to add harmonics 64 to 126). To help overcome this, the K5 offers a whole range of time-saving functions to allow you to get where you're going as quickly as possible. The first of these is the Increment Dial. This allows you to very quickly change the level of whichever harmonic(s) is (are) selected. Combine this with the excellent 60 x 240 bit-mapped LCD display of all 63 harmonics (Figure 1), which you call up with the DHG (Digital Harmonic Generator) button, and you have a very simple way of changing the level of each harmonic and keeping track of what you are doing.
But even using this method it can take quite a while to knock 63 harmonics into shape, so Kawai's designers have come up with a few short cuts, to speed things up. By moving the cursor in the display to 'All', you can change the level of all 63 harmonics when you use the Increment Dial. This actually increases or decreases the individual harmonic levels relative to their starting positions, so it doesn't automatically make all the levels equal (which would be pretty useless) although you can do this very quickly by maximising all the levels (if you want to start afresh, for example).
Of course you won't want to be moving all the harmonic levels together all the time, so there are several other groupings available. You can choose to alter Odd (3, 5, 7, etc) or Even (2,4, 6, etc) harmonics separately - this is useful as many standard waveforms have completely different levels for odd and even harmonics - or, alternatively, Octave or 5th interval harmonics. This allows the harmonics which are octaves of the fundamental (2, 4, 8, 16, 32) or fifths (3, 6, 12, 24, 48) to be altered as a group - very useful when programming organ sounds, as these harmonics tend to be the ones available on organ drawbars.
These groupings may include harmonics whose level you have already deliberately reduced to zero, because you don't want them present in the sound. Thus, if you increased the level on a group which included such silent harmonics, you would bring them back into the sound. Now that may be what you want, but equally it may not. So the clever chaps at Kawai have given you the opportunity to choose whether you want to 'resurrect' silent harmonics or not. 'All' alters the levels in the group of harmonics whether currently sounding or not; 'Live' just alters those that are currently sounding (ie. whose level is not 0). And if you just want the harmonics in any group which have been turned off, then you select 'Die' (cheerful stuff this!).
If these 'preset' groupings of harmonics are not what you need at any point, you can also determine for yourself a range of harmonics to work upon. You do this by entering the lowest and highest numbers of your range on the keypad - say 7 and 43 - and all the harmonics from 7 to 43 (the currently selected range is shown as a horizontal band across the bottom) will be affected when you move the Increment Dial. You can, of course, use this range in conjunction with the groupings so you could alter just the even-numbered harmonics between 7 and 43 or all the 5ths between 17 and 60, for instance.
So the K5 gives you unprecedented flexibility when it comes to selecting which group of harmonics you want to work on. But so far, any movement of the Increment Dial would work on all selected harmonics equally. However, the cunning of Kawai's programmers has not been exhausted yet. Most natural sounds have much louder lower harmonics (if you want the physics behind this, it's because higher frequencies require more energy to produce the same volume) and you can achieve this on the K5 using 'Angle', which attenuates one end of the harmonic series more than the other. If you give 'Angle' a positive value then the higher harmonics will be attenuated more, which is how the acoustic world does things. Of course, the nice thing about a synthesizer is that it doesn't have to be confined to the same rules as natural sounds, so it's nice to know that by entering a negative 'Angle' value we can actually reverse the natural order and attenuate the lower harmonics more.
"Unlike all previous implementations of additive synthesis the Kawai K5 allows you to hear all changes to the harmonic structure as you make them."
All in all then, Kawai have gone further than previously possible in making additive synthesis a manageable technique, both in terms of the time required to set up a combination of harmonics and in the ease with which you can keep an immediate check on your efforts, both audibly and visually.
So far we have only looked at harmonic addition to produce a static waveform - the beauty of the K5 is that, unlike other additive synthesizers, you are not restricted to this. Instead of having to use frequency modulation or analogue filters to introduce some harmonic development and interest in the sound, we can achieve timbral change by altering the volumes of the harmonics in real time, ie. while the note is sounding.
This is achieved in two ways. Firstly, you can specify whether each harmonic will be modulated by turning a dot above that harmonic's level column on or off in the display. This means that you can decide independently for each harmonic whether modulation will affect that particular harmonic component. This has to be the most flexible assignment of LFO effect that I've seen on any synth at any price. It means that you can apply vibrato or some other modulation effect to just part of a sound or even to several of the many elements within the sound. This is typical of the flexibility of the programming system of the K5.
The second way in which harmonic change and interest can be introduced into the additive waveform is via no less than four envelopes. Each harmonic can be independently assigned to any one of these four envelopes, which are (like everything else on the K5) nothing if not complete, having six stages. We will look at them in detail a little later.
Of course, selecting modulation and envelope routing for each harmonic could lead us back to the old bugbear of additive synthesis, the amount of time it takes to set up a sound. Fortunately, each of the groups (All, Odd, Even, Octaves or 5ths) of harmonics we saw earlier can be used to globally assign its member harmonics to a particular envelope or switch modulation to them on or off. This means that you set up the general assignment very quickly and then make adjustments to individual harmonics as required for fine tuning.
So far, everything we have discussed can be accessed from one 'page' on the K5's LCD screen, the page known as the Digital Harmonic Generator, called up by pressing the DHG1 button. This makes the process of setting up the basic waveform much simpler, as you don't have to keep calling up and changing different parameters (which can easily make you forget where you were in the sound).
The next page you will probably want to use is the DHG2 page, which controls the amount the envelopes are affected by velocity, pressure, LFO mod and keyboard scaling. But to make it easier to see how each envelope is assigned and to hear the change to each, not only does the bar chart of the DHG1 page reappear on DHG2, but you can 'solo' or defeat any or all of the envelope groupings. When you turn any envelope off, the harmonics assigned to it disappear both from the audio output and from the LCD bar chart.
As if this wasn't enough, this DHG2 page offers you an 'Effect' for each envelope: this is actually a separate modulation rate for each envelope group. So each of the four envelopes can be set to modulate at different rates, increasing the complexity of the resultant waveform and, therefore, how interesting it is to the ear.
The envelopes on the K5 - those for the harmonic levels, as well as the one for pitch (Digital Frequency Generator envelope) and those tied to the DDA (Digital Dynamic Amplifier) and DDF (Digital Dynamic Filter) - are all very highly evolved examples of the species. They all have six stages, which are set by six Rates and six Levels in a manner with which most of us are now familiar, having seen them appearing not only on pure digital synths but on digitally-controlled analogue hybrids.
The DHG envelope page actually allows the four envelopes controlling the levels of the different groups of harmonics to all be seen at the same time (see Figure 2). This is very handy as it lets you compare how the different harmonic groups interrelate during the course of the sound. A double vertical line shows where the sustain level of all the envelopes is - between Level 4 and Level 5. In other words, when the envelope reaches Level 4 it stays fixed at that level until the key is released. Apart from this fixed sustain point, the rest of the envelope is completely flexible as to which stages are the attack, decay or release portions.
Another nice feature of the envelopes is the 'Max Seg' function. This allows you to set any stage to be full (ie. maximum) level, and develop your envelope around that. This enables you to be sure that you are using the full range of your parameters, maximising dynamic range and keeping digital noise (which results from using just a small part of the envelope's level range) to a minimum.
"The envelopes on the K5 are all very highly evolved examples of the species."
Having four envelopes for the harmonic amplitude (in addition to the pitch, filter and overall level envelopes which most other synths would regard as more than complete), the danger of time-consuming programming again rears its head, but the Kawai boffins have come up with another scheme for saving valuable time. The 'Shadow' feature allows several envelopes to be set up simultaneously by automatically copying any parameter changes to all the higher numbered envelopes. In other words, if you alter Rate 3 of Envelope 2 (with 'Shadow' on), then Rate 3 of Envelopes 3 and 4 will be altered to the same values, but that of Envelope 1 remains unchanged. This, again, means that you can achieve the coarser setting up of the envelopes fairly quickly and then make any changes between the different envelopes as individual adjustments.
When talking earlier about the envelopes, I mentioned in passing that the K5 has one envelope 'hard-wired' to the filter (DDF). But it may come as a surprise to many people that the K5 has a filter at all! I've heard it argued (mainly by synthesizer designers) that if you have the flexibility and precision of additive synthesis with multiple harmonic envelopes, a filter is redundant. It is clear to me, however, that people who maintain this viewpoint are essentially theorists or have never had to create a new sound under pressure. The filter is perhaps not the subtlest of sound-shaping devices, but there is nothing else quite as fast and effective for making radical changes to a sound. Sure, if you have the time you would use just the harmonic envelopes to sculpt as finely-crafted a sound as you like, but the majority of us need our synths to be quick as well as accurate. Thankfully, Kawai have not fallen into the trap of leaving a filter off their synthesizer just because all things are theoretically possible using just digital techniques.
However, the filter on the K5 is not analogue but digital. 1987 has really emerged as the year when the all-digital filter finally arrived. First, the Roland D50 with its TVF (Time Variant Filter) - now available on the S550 sampler too, and now the Kawai K5. At the moment though, digital filters are still configured to look and act just like analogue ones, so the K5's filter parameters are very familiar. There's our old friend the 'Cut-off Frequency', which can be modulated by the LFO, envelope, velocity, pressure and keyboard scaling. However, being digital, the 'shape' of the filter effect can be more precisely set than on its analogue counterpart. 'Flat Level' sets a general level for the filter and 'Slope' determines how sharp the transition is between 'Flat Level' and 'Cut-off' (Figure 3). If you set 'Flat Level' to 0, then the DDF acts like a band-pass filter with 'Slope' determining the width of the frequency band. Setting a very steep 'Slope' value between the 'Flat Level' and 'Cut-off gives the same effect as a high Q setting on an analogue low-pass filter. But because of the way the K5 filter is configured, you can set up interesting combinations of the two.
'Slope' can also be modulated by all the same sources as the 'Cut-off, ie. envelope, velocity, pressure and keyboard scaling, but the two amounts can be different. This means that on one patch you could have Cut-off greatly altered by velocity, but no Slope modulation, whereas on another you could have pressure increase the resonance through the Slope, but only slightly raise the Cutoff level.
A similar set of parameters can affect the Digital Dynamic Amplifier, but with attack and release velocity being separate modulation sources. The envelope is now expanded to seven stages, with the ability to decide which of the envelope Rates is affected by the modulation coming from attack velocity, release velocity and/or keyboard scaling. This might be all seven stages or just one or two: any permutation is possible.
The programming parameters of the K5 that we have seen so far are extremely complete, but you may be surprised to know that I've only been telling you half the story! Everything discussed so far is doubled in a second sound source - all 63 harmonics, filter and amplifier envelopes, the lot!
The two independent sound sources can be combined in two possible ways: Twin Mode or Full Mode. Twin Mode combines the two sources in much the same way as two oscillators on a standard synth, allowing you to set up intervals or de-tunings to fatten up the sound (always a good idea on digital synths), layer the two sounds together and/or crossfade between them (by assigning each a different velocity response), and so on.
Full Mode uses the second source to add in a further 63 harmonics in continuance of the harmonic series. This is really useful on deep bass notes as you can tailor the harmonic movement across the whole 20kHz audio bandwidth (on anything else, all these high frequency harmonics can only be fully appreciated by dogs, bats and other animals who can hear outside the range of human hearing).
Whichever mode you use, the sound of both sources is added together and passed through another digital filter. However this one, the Digital Formant Filter (DFT would you believe?), is configured to behave more like a graphic equaliser. Figure 4 shows the LCD screen which appears when you call up the DFT page on the K5. The equalisation bands are arranged in musical pitch (ie. octaves) from C-1 up to C9. I liked this as I never really felt able to relate to 'Hz' and 'kHz' in terms of pitch.
To adjust the EQ you just pick an octave of C and use the Increment Dial to alter its level (from 0 to 63). Like all the other pages of the K5 display, one of the most useful features is that you can switch the thing you are working on in and out of the audio chain, just like on a mixing desk, so that you can hear exactly what difference that section is making. This, of course, is something we are used to doing with EQ, but it is equally useful on standard filtering or harmonic envelopes.
"The completely real-time variability of the harmonic structures, both in editing and performance, makes the Kawai K5 a much more programmable and expressive instrument than any previous additive system."
The Low Frequency Oscillator (LFO) on the Kawai K5 is as complete as the rest of the machine, having six available waveforms (Figure 5). One of the nice things is that all the inverted waveforms are available, so in Twin Mode you could have both sound sources the same and then invert the modulation of one to make the sound richer. The 'Delay' and 'Trend' LFO parameters give you extra control over the introduction of the modulation; 'Delay' determines how long after a key is pressed it takes for the LFO to begin operating, and 'Trend' (nothing to do with fashion!) sets how long it takes to reach the programmed full modulation depth. Those who have another keyboard part to play with their left hand should appreciate this facility.
The final page of the individual sound programming covers 'Keyboard Scaling', which we have been happily routing left, right and centre as we explained the other pages. Once again, the K5's LCD helps you appreciate just what you are setting up (see Figure 6). Keyboard Scaling has really evolved from the old 'keyboard tracking' on analogue machines but, as with everything else on the K5, the facility has been heavily refined. Here, you can set the filter to close more rapidly the higher you go above the 'Break Point' (but not below) or cause the effect of velocity to diminish as you move down the keyboard.
Once you have set up your individual patch (which can consist of two completely different sounds layered in Twin Mode, if you like), then it is time to start seriously combining sounds in Multi-Patch Mode.
As I have probably spent too long explaining Single Mode (although it is well worth examining in detail), I think the quickest way to appreciate how Multi-Patch Mode works is by analogy with a multi-sampler. Although each sound on the K5 can be played over the full MIDI note range, you can tailor different patches to work best in a particular octave and then assign a different patch for each octave. Or you can layer many patches on one key. The K5 is 16-note polyphonic so you can have lots of sounds layered or split across the keyboard. The combinations and possibilities far outweigh those of any other synth I've ever seen (and, indeed, many a multi-sampler).
On Multi-Window 1 (see Figure 7), you can select up to 15 different sounds to be used in your Multi-Patch. You can assign each one a keyboard range (called a 'Zone'); specify the maximum polyphony of each sound (from 1 to 16 notes, or 'VR' - meaning variable, often referred to as Dynamic Allocation); select whether each sound is to be triggered from MIDI (eg. via an external sequencer), from the keyboard, or both ('Mix'); and which MIDI channel it is to be controlled by. And that's just on the first Multi-Window page.
On Multi-Window 2, you can set a Velocity Switch range, Transposition Detuning, and Level, as well as assign each patch to one of the K5's four separate (polyphonic) outputs. Multi-Window 3 covers the routings of the expression controllers including Pedals, Wheels, Volume and MIDI Controllers, all of which can be set individually for each patch within the Multi-Patch. This is continued on Multi-Window 4 with Hold (Sustain), Portamento On/Off, Program Changes, and Velocity.
The Data Management pages deal with all those vital but rather dull features, like writing sounds to protected memory, loading and saving from RAM card (yes, Kawai are using the new slim-line credit card approach to RAM too!) plus the invaluable 'Compare/Recall', which continuously allows you to check your progress when editing. It also allows you to go back to the edited sound even if you hit a new patch or the power is accidentally switched off (what a life-saver!).
MIDI on the K5 covers everything from System Exclusive patch dumps to enabling/disabling MIDI pressure (something other manufacturers would do well to implement) and each parameter can be independently set for Transmit and Receive modes. Once basic parameters have been set on the overall MIDI pages, you can then go in and customise each Multi-Patch for multiple channel receive (Mode 4) and independent response to the various switches and controllers.
The System/Link page covers the ability to set different Velocity Curve responses from the keyboard, switch Local Control on/off, as well as basics like Master Tune and Keyboard Transposition. Link allows you to chain together a series of Multi-Patches for fast changes during performance.
All in all, the Kawai K5 is quite an achievement. It is the first polyphonic synth that makes additive synthesis quick to use, easy to understand and simple to programme. And it costs considerably less than a Macintosh computer, Digidesign's Softsynth program and a sampler, which until the release of the K5 was the cheapest and best way to get additive synthesis in polyphonic form. But the K5 is streets beyond that system's rather antiquated approach of edit, re-compute, transfer from computer, save to disk. The completely real-time variability of the harmonic structures, both in editing and performance, makes the Kawai K5 a much more programmable and expressive instrument than any previous additive system. It means that it can compete directly with the DX7IIs and the D50s as a performance instrument which is as exciting to play as it is to programme. And whilst not all the factory sounds are stunning, there are enough good ones to keep you going until you develop sounds of your own.
It's good to see that Kawai, in the short time that they have been in the field of hi-tech electronic instruments, have not contented themselves with emulating the designs of other successful companies but have bravely developed instruments which stand on their own merits. Their R100 and R50 drum machines were a great start, but in the K5 they have rejuvenated one of synthesis's oldest techniques and dragged it into the Eighties to make a truly expressive, performance-oriented synthesizer.
Price K5 keyboard £1495; K5M expander £1045 (both inc VAT).
Contact Kawai (UK) Ltd, (Contact Details).
Review by Paul Wiffen
Previous article in this issue:
Next article in this issue: