Digital Drum Machine
Marcus Ryle of Oberheim Electronics introduces the review by talking about his design
"The DX is a digitally sampled drum machine that was designed after our DMX digital drum machine. We took out the modular voice card design which the DMX has, which has user changeable voices in order to bring the cost down to £1,000 retail in the UK, but we didn't compromise at all on any of the sounds that are in the DX so we still have the same high-quality recordings that we had in the DMX. The DX has three volume levels of bass drum, three volume levels of snare drum, two volumes of closed hi-hat and open hi-hat, three toms, three volume levels of crash cymbal which is a long crash cymbal by the way, two volumes of shaker and hand claps. It also has the same memory capacity as the DMX which is 100 sequences at 50 songs and will store approximately 2,200 events, ie drum beats, which is more than twice as much as the competition in that price range. We still have the direct outputs on all of the drums, and the clock in and out so it'll be compatible with 'the system' ie. the DSX and the OB-8.
There is no MIDI interface on it but we're currently looking into MIDI and our stance currently is that we will most likely put it on future products. We have a parallel interface we've been doing for about three years which is of course much faster than MIDI and that's how we do our sequencer to synthesiser interface. The transmission is very fast and we've been very happy with that interface but it's too expensive for a lot of the other manufacturers to get into. We have to have a 37-pin connector and the other manufacturers wanted to do something that was more affordable of course. We will probably be including MIDI in the future but we wouldn't be able to do everything that we are currently doing with our own interface system as it's not as versatile nor is it as fast. So as far as the DX is concerned, the interface is done with the clock in and clock out which we feel, at least for the moment, is sufficient information to do just about anything you'd want to do with a drum machine.
You can always use the clock out to drive the other machines in any case, which is exactly what we usually do in a normal set up of 'the system'. The sequencer's clock input is able to sense when the clock starts up and it automatically jumps into play (it doesn't need to be told 'start at the beginning of the sequence here'), and it also notices when the clock stops to go into stop, so with an ordinary jack-to-jack from the clock of the drum machine to the clock of the sequencer, you can start both machines from the drum machine.
The clock pulse is 96 pulses per quarter note whereas the TR808 is actually 24 per quarter note and I think the Linn Drum is 48. They are even multiples of each other so you can use them all together. The DX has more resolution than the others do but they can all function together.
The DX has all real sound samples. It's certainly the most realistic way to get drum sounds. We've been working on it now for quite a few years, we have a dedicated computer system for doing the sampling — it allows us to edit the sounds and alter them in computer memory and get them to sound just the way we like them. The tom-tom sounds are the same samples but tuned differently. Each voice card or each set of three buttons on the DX and the DMX are a single voice consisting of one DAC, a counter and some memories. Sometimes the memory is one sound with either different pitches or different volume levels, sometimes the memory is divided for two separate sounds. The toms are one sound recording at three different pitches whereas in the DMX we have two separate tom recordings, each with three different pitches giving six toms. There is one recording of bass drum but three volume levels of that same sound, the snare sound has three volume levels and so on.
Each drum has a tuning pot on the back panel. The cymbal tuned all the way down sounds quite a bit like a gong in fact. Your readers may also be interested that on the DX all of the tunings are in fact voltage controllable — there's actually no connector inside but the tuning pots on the back go to a connector on the board and are simply providing a voltage for each drum for the tunings so if a hobbyist wanted to have something else actually controlling the pitch, you could do that. The voltage range is 0-5V.
The DMX actually has a connector on the back with eight individual control voltage inputs that can control either pitch or volume of each of the voices which enables you to do quite a few other things. It also has eight trigger inputs to trigger the drums. If you wanted to, you could use an external computer to be changing all those things as well. There's a gentleman in the United States who's taken a set of practice pads and designed a little circuitry and has it set up so that hitting the snare drum harder adjusts the volume. The thing sounds amazingly like real drums which are continuously dynamic on all sounds.
I think the most important thing that we did in designing this was not to skimp on the amount of memory necessary in order to get a good sound. We're sampling at a significantly higher rate than the other machines which means it takes more memory but I think we result in a better sound. Certainly the crash cymbal is a difficult one and it takes up the most memory space. The chips in the DX are 2764 EPROMS, and there is one for each of the five standard voices and then there are 4 x 64s, that's 32K of memory, for the crash cymbal.
The bandwidth is dependent on the pitch of the sound, but I believe, with the pitch of the cymbal, it normally ends up we're actually sampling at a rate close to 40kHz. Some are between 35 and 40k, and it's quite a bit higher than the others, because you really need the high end. The crispness of the cymbals is what seems to show through. The hand clap is also sampled. In fact, out of all the sounds it is probably one of the most difficult because even when you get a hand clap recording good enough to make it convincing, you have to have a hand clap recording that will sound convincing when it's repeated and real hand claps are different every time. A lot of factors go into what someone might call 'good handclaps'. What we actually did was simply record quite a few sets of handclaps, digitise a number of different ones and then one of us took a survey of what people liked and came up with what we think is a really useable hand clap, even though it is the same every time.
We're very happy with the sound quality we've achieved. It's been an Oberheim philosophy to always put the sound first and sometimes that means our machines end up costing a little more but we don't want to compromise on the sound — that's really what our name has been based on, it's very important to us. There's no glitching at all in the DX. Not only did we digitise the sound and put a DAC in there, but we carefully selected all the components to fine tune each voice individually so that it sounds best for that particular purpose. For example, the cymbal you want to have nice high end. On other sounds that may not be as important as having a long sustain sound and so on.
We have about eight engineers in the Engineering Department and we all work on different facets of the product. The Oberheim Organisation is not really a very specialised, very small cottage industry anymore, with 'the system' and how it's grown over the last few years. We have all of our manufacturing in house as well, we have approximately 80-90 employees, and these machines are being turned out at quite a fast rate now. We're certainly producing quite a few DXs. It's already available on sale in the UK at Chase Musicians and Rod Argents is also a dealer for it.
I think sound sampling will be important in the future, not just with drums, but each individual type of sound has to be addressed separately because they all have specific problems when they are sampled. We find that drums are particularly well suited to sampling and the techniques we use. There are other instruments which when sampled are less realistic. I would be hard pressed to call what some machines call a sampled violin a 'real' violin. These are very difficult for all involved and since at Oberheim our main concern is with the sound, we do things that sound good and if we can't make something sound good, we won't put our name on it."
The instrument comes in the classic Oberheim livery, a wooden-ended metal case with a blue-striped sloping front panel, 18 inches wide, 12 inches deep and 5 inches high. Apart from the volume sliders, all the programming controls are the sturdy, ¾ inch square buttons which seem to be 'de rigeur' on all the professional quality drum machines. These are uniform black with the exception of the white Play/Stop and the red Record buttons. All Mode Function buttons (as opposed to Instrument buttons) have an LED set in them, which tells you at a glance if they are in operation. On the left hand side, there is a numeric key-pad with four 7-segment displays immediately above to give status readout in the various modes of operation, and above this is the standard illuminating mains switch.
For substantially less money than the DMX, the DX still features most of the instruments it's big brother has, with three Bass Drum buttons, three Snare buttons, Hi-Hat (Open, Closed & Accent buttons), High, Mid and Low Toms, Cymbal (Soft, Medium and Loud buttons), two Shaker sounds and last but by no means least, the increasingly popular Claps. These are tidily arranged in columns of three from lower right to lower middle of the panel. Immediately above each column is its individual volume slider and the instrument name, presenting a very neat and clear layout. The first column is the Bass Drum and has a button each for Soft, Medium and Loud. This allows considerable subtlety of accent to be programmed into a rhythm pattern, whatever the overall mix of the instrument set on the volume slider. The actual sound (a digital sample of real drums as are all the sounds) is as 'meaty' as one could wish with a nice distinguishable 'smack' from the pedal. There is no loss of power in the sound even when it is retriggered rapidly, often a problem if the rise time on a bass drum is more than 5mS. The next column along, Snare is organised on a similar basis, Soft, Medium and Loud in descending order. Again full marks here for a good solid full sound, entirely acoustic in feel and a welcome relief from the synthetic, over-resonant snare sounds featured on many records these days. Again two separate sounds, the stick against the head and the snare spring can be heard. The interplay of just Snare and Bass sounds at the Accent levels enable some very powerful rhythms to be created.
The Hi-Hat column assigns the three buttons slightly differently, uppermost to Closed, middle to Accent and lower to Open. A small point but I would have felt more comfortable with Closed at the bottom and Open directly above it as I found 'real time' programming a little awkward. No such complaint about the sound, however, with the Open to Close transition being particularly effective. Oberheim have taken great care to keep the bright clear characteristic of quality hi-hats and cymbals by not skimping on the resolution necessary to capture the high frequencies. The Tom sound (next column of buttons) is equally good, being a great improvement on the original DMX tones. The pitch is clear without the resonant 'ring' of some toms and there is plenty of depth. The only problem is really in terms of triggering. As all three Toms (High, Mid and Low buttons) are the same sound off one chip read out at different speeds for different pitches, it is not possible to get two toms sounding simultaneously and in a roll the triggering of a lower (or higher) tom causes the first tom to cut off sharply. This is clearly something dictated by economy (the DX does represent extremely good value-for-money) and need not be a problem with careful programming as long as one is aware of it. 'Real time' programming of the toms can be a little tricky as the 3 buttons do not fall naturally under the fingers in the column, but this is a natural result of the logical layout of the instruments. A slight sidewards approach can help this positioning.
The Cymbal column reverts to the Soft, Medium and Loud buttons, and it is this sample which is the triumph of the DX. By using 3 chips on this sound, they have achieved both high resolution and length giving one of the most authentic cymbals available. In Soft or Medium, it a very crisp 'ride' on retriggering, whereas Medium gives a nice 'splash' effect and Loud gives a good enough enough 'crash' to end a track with. The decay on its lasts a good 10 seconds and is free of all glitches, dying smoothly away without any rise in background noise.
The Perc column is perhaps the most disappointing. It features 2 Shaker sounds and Claps (an indispensable addition to any drum machine these days). The Claps are excellent and have a nice ambience as well as a sharp attack. They retain authenticity even on fast retrigger and mixed in with the Snare give an almost inhuman crisp backbeat (a la Bruford snare sound). However, both Shakers are disappointing. Never the most useful of percussion, they seem rather weak in comparison to all the other excellent sounds and even at full volume tend to both get lost in the mix and at the same time render the crisp rhythms of the other sounds somewhat 'woolly'. I would have preferred the retention of either the rim shot or tambourine sounds of the DMX, which have a greater clarity.
The DX programmer allows you to choose the way you record your rhythms. Real and Step Time are available, or the two can be used in combination. Using whichever method, patterns from 1 to 99 measures (bars) can be built up and then chained together into 'Songs'. There are 50 Song locations available and each can take 255 events. As memory is shared between all locations it can be used in a variety of ways to maximise the potential and if the potential is all used up, the display shows 'Full', the DX 'beeps' and it is impossible to erase patterns already recorded, unlike some sequencers and drum machines which start deleting from the beginning or ignoring further commands.
A metronome is provided to facilitate real time recording and its volume slider is immediately next to those of the instrument columns, with the master volume slider last in the row. The metronome is heard through the mix out when in 'record' mode, but is always available as the 'Click Out' from the Click Output jack socket on the back. The metronome can play minims (1/2 notes), crotchets (1/4), crotchet triplets (1/16), quavers (1/8), quaver triplets (1/12), semi-quavers (1/16), semi-quaver triplets (1/24) or demi-semi-quavers (1/32) (allowing 48 notes per 4/4 bar sequences to be triggered using the 'click'). The metronome ('click') can be changed at any time before or after recording which is very convenient. Nothing is more annoying to have written your drum pattern than to discover that you have to rerecord it with a different click speed. With this facility you can change the click halfway through to help you record a tricky hi-hat line, for example, or change it afterwards to come in line with a sequence.
The DX defaults to two measures in record mode but by pressing Length, you are able to alter this to any length from 1 bar to 99. Similarly the bars default to 4/4 but by pressing Signature you can alter the number of beats in the bar and pressing Signature again allows you to change beat length from 1/2 to 1/32 notes. The Quantize feature is an auto-correct function which can be set to correct to the nearest 1/4, 1/4 triplets, 1/8, 1/8 triplets, 1/16, 1/16 triplets, 1/32 or 1/48. It can also be defeated (switched off) to allow resolution down to 1/192 of a bar. Tempo defaults to 80 beats per minute but can be adjusted by pressing Tempo and entering the number of beats per minute from 25 on the numeric up to 250 BPM on the numeric pad in a similar manner to the other 3 functions which control the recording process, but this function can also be accessed during playback. Tempos inserted in record are remembered and reproduced on playback, but they can be over-ridden in playback. Different bars can have different tempos, clicks, quantizations as well as different time-signatures, in other words each bar is independently programmable.
This method of recording allows you to assign a note value from 1/2 to 1/64 to a step, any number of steps to a bar and any number of bars from 1-99. On each step, up to 6 instruments can be recorded until the desired pattern is created. Tempo can also be set while recording.
This is an extra function in real-time record and acts in the same way as Quantize, that is to say it 'corrects' your playing to programmable limits. The DX defaults to 50% swing which means that the second 'half' of the beat takes up the same amount of time as the first 'half.' However, by increasing the percentage you can extend the amount of time the first 'half' takes at the expense of the second (keeping the beats themselves constant). At maximum (70%), this gives the equivalent of two triplets to the first 'half' and one to the second. This gives a pacy, more human feel to the beat. However, as Swing is a Record/Auto-Correct function, it is not possible to remove it if you do not like the effect produced. Any lines recorded in this manner must be erased and re-recorded after the Swing has been reset.
This is one of the strongest points of the DX. Before using the Song Feature it is possible to expand and combine the simple sequences themselves and store them in one sequence location (allowing longer and more complex songs to be stored).
Firstly, one can copy any sequence from one location to another. But by holding down Record as well as Copy, one can add a sequence to another, ie. Appending. This can be done until 99 bars have been stored in one sequence location. The practical upshot of this is that entire 'verses' 'middle eights' and 'choruses' can be stored in one location. It is possible to append sequences to themselves, to append sequences in different tempos or time signatures and to create complex pattern changes within one memory location by these means. This quite often means that you do not need to use the Song mode at all. However, for those who need long, constantly changing drum parts (Jazz- and Progressive-rockers) this is the section for you. Now let us look at the programming of chains.
As with most drum machines this is called Song Edit. Whereas there are 100 sequence locations (fairly standard for this type of machine), there are also 50 song locations (considerably more than the competition at the same price). This means that a typical length 'set' can easily be stored without making use of the cassette dump facility. Few people will perform 50 songs in an evening, so the only limitation is the 220,000 event storage.
Programming songs is simplicity itself: one simply assigns a sequence number to each of the (up to) 255 events in a song. The only other function which needs to be assigned is End. Repeats are unnecessary as these can be inserted into the sequences themselves using Copy/Append. Songs can be re-edited at any time, and can be of any length. An overall tempo can be set which proportionally speeds up or slows down the individual tempos in each sequence (an extremely useful function which saves having to reprogram each individual sequence if a slight tempo change is necessary).
At the right end are the six presets controlling the tuning of the six columns of sounds (unlike some drum machines which have no tuning facility or others with only one overall tune). Basically this adjusts the speed at which the digital information is read out, and changing the frequency alters the pitch. Again, as the three toms are all one sound, the tuning adjusts the pitch of all three simultaneously, but the other instruments are all individually tunable, a very useful feature indeed. Perhaps the knob range is a little wide (the highest and lowest pitches are a bit extreme), but this is far better than having a limited range, as careful adjustment allows the necessary accuracy of tuning.
Below these are the six individual outputs, plus the click output (programmed using the Metronome). The volume of these outputs is unaffected by the sliders on the front panel (which are only active on the mono or stereo mix) allowing them to be put through a mixing desk and equalised and mixed individually as required.
Next to these we have the three mix outputs, Left, Right and Mono, allowing the full mix to be heard if only one amp channel is available, or a stereo spread if two channels are used. Then come 2 footswitch inputs, Start/Stop and Next (for advancing the sequence/song number). Trigger Input allows the machine to be externally triggered and Clock In/Out allows Sync to Tape for which the software update will soon be available. Above all these jack sockets are two switches, the all-important Memory Protect and Cassette Interface Enable.
This is accessed by two standard jack-sockets (as opposed to mini-jack sockets, as is so often the case — I wish more manufacturers would follow Oberheim's example as mini-jacks are so much more delicate and difficult to make up into leads). The Song, Edit and Step Buttons double as Check, Play and Record Functions when the Cassette Interface Enable Switch is on. With the Interface it is possible not only to dump programs onto tape and reload them into the DX, but by playing them back in again, the DX can be made to check the information coming in against that already loaded and verify that the two are the same. The whole process takes only a few seconds and is extremely reliable.
The processor which runs the DX is the Z80 (CPU). There is 16K of firmware (for instructions) provided by two 2764 chips and 8K of CMOS RAM (four 6116 chips) with battery back-up to handle the system and programs.
The Bass and Snare Voices are each stored in a 2732 chip (4K of memory) and the Hi-hat and Toms have a 2764 (8K of memory) each, as does the Perc channel. The remarkable Cymbal sound uses no less than four 2764s (that's 32K of memory) to allow the necessary resolution and speed for the higher frequencies it contains.
Each voice has a counter, clocked by a 555 oscillator. The frequency of the clocking is adjusted by voltage control from the tuning presets on the rear panel. The stored data goes through a companding DAC (one for each voice, hence the extremely high quality of the DX's sounds) and is then filtered to remove quantization noise before being connected to the final mixer at the respective output. It is the way in which each voice is separately clocked, controlled, converted and filtered (unlike most of the other machines in this price bracket) which has led to the high quality and independent controllability of the sounds.
Oberheim have not let their standard slip whilst producing this competitively-priced digital drum machine. It looks good, it sounds very good and it has lost none of the memory space and programmability which usually accompany the modification of a more expensive product to a more economical price bracket. Indeed, to my ears it sounds better than the DMXs I have heard. I am told in fact, that the specially recorded new sounds for the DX are now available for the DMX as well, and this is the beauty of this system, that all the sound chips are user-replaceable. To get a new drum sound, a better drum sound or even just a different drum sound (and at this quality level, it is all really a matter of personal taste), you don't need to buy a new machine, just a new chip with a different sound stored on it. This, coupled with the extensive memory both of sequence length and song location together with the ease and flexibility of programming, makes this drum machine a good longterm investment.
The DX drum machine can be seen at Chase Musicians, (Contact Details) who are the Oberheim importers for the UK. Their current price on the DX is £999.
Review by Paul Wiffen
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