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Peavey DPM3

Composition Centre

Announced over a year ago, the all-American DPM3 has finally landed on our shores. Martin Russ takes the wraps off Peavey's much publicised first foray into the hi-tech keyboard market.



Suppose that Ensoniq had designed the Roland D50! Imagine the Korg M1 with a disk drive and a better sequencer! What would you expect the first ever synthesizer from a guitar combo manufacturer to be like? The answer to all of these questions is a fascinating new instrument which potentially offers much more than is readily apparent at first glance: the Peavey DPM3.

Peavey call the DPM3 a 'composition centre', which at first sounds like just another synonym for the current buzzword 'workstation', but in fact imparts less of the 'this is all you'll ever need to buy' feeling that many manufacturers seem to convey, and more the idea that the DPM3 can form the nucleus of a comprehensive music composing system. All the vital elements are present: a powerful and versatile 16-note polyphonic, 16-voice multitimbral 'sample+synthesis' sound generator, which incorporates a drum machine, a 9-track/20,000 event sequencer, two digital multi-effects, and floppy disk drive.

PROGRAM STRUCTURE



The DPM3 deliberately hides the difference between a single sound (often called a 'patch', harking back to the days of patch leads on analogue synthesizers; or a 'program' - a term influenced by the computer-based instruments that proliferated in the '80s), which is the fundamental editing and timbral component of the instrument, and a collection of sounds designed for use when performing (usually called a 'performance'). Peavey combine the two into a single unified concept: the 'program'.

Some 100 programs are accessible from the DPM3's internal memory at any one time, and these betray little evidence that they are actually split into two types: singles and multis. A single program is just that - one sound, whilst a multi program is an arrangement (of keyboard splits, detune, MIDI channel, range, and layers etc) of single sounds. As far as the user is concerned, when a DPM3 program is selected, you hear a certain sound when you play the keyboard and the mechanics of how that sound are produced can be left to the sound programmer, or ignored until the sound needs to be edited.

FRONT PANEL FEATURES



The front panel controls and the keyboard itself are the main way in which a player will interact with any synthesizer. In this instance, the front panel buttons are black, like the panel itself, and very low profile with a light and shallow movement - a potential nightmare on a dimly lit stage with sweaty fingers. In monochromatic light, the small italicised blue lettering used to identify the lower ranks of buttons might be difficult or impossible to read, although the salmon pink colouring used for the other control legends should remain readable. Not quite what you'd expect from a company whose reputation is built on live performance oriented equipment, is it?

The top left of the front panel houses the program selection buttons. The 100 programs are arranged in 10 banks of 10, and the banks are selected by pressing one of five selection buttons either once or twice, ie. button 1 accesses both banks 1 and 6; button 2 accesses banks 2 and 7, and so on. The sixth button in the group toggles between internal and cartridge programs (100 programs can be stored on the optional 32Kbyte RAM cartridges). Once a bank is selected, the 10 program names (six characters per name is far too few!) appear on the centrally located, backlit, green LCD. Two rows of 40 characters gives rather limited visual feedback by today's standards. Surrounding the display are 12 'soft key' buttons, as seen in the ESQ1, D50, and SY77 etc; the leftmost pair move up and down through pages, or banks of programs in this case, and the remainder select the option.

Closest to the player's left hand are the four System Control buttons. The Master button provides a menu of choices for a mixture of housekeeping and related tasks: master tuning, effects, sample RAM management, MIDI controllers etc. Similarly, the Storage button deals with the edit buffer and the disk drive, cartridge and MIDI input/output. The MIDI button calls up a page devoted to the major MIDI control parameters of the instrument, whilst the Compare button serves only to toggle between the original and edited sound.

Falling easily under the left hand are the two slider controls, one for volume and one for data entry. These are well recessed and have the same black-on-black colour scheme as the buttons, with no markings at all. I am not sure about the validity of having the volume and data entry controls so close together in this way, especially when you can assign the data entry slider to act as a 'live' controller for parameters within the programs. Forget which is which and there might be a few embarrassing silences midway through that important solo!

To the immediate right of the LCD are the remainder of the value controllers: an alpha wheel and increment/decrement buttons. The wheel is not detented, so you need to watch the display as you turn it instead of using tactile feedback. I would have preferred a numeric keypad, especially when trying to set zero values for parameters, which can be quite tedious with the present wheel and increment/decrement buttons.

The far right provides a home for four rows of buttons: the top two rows access the sound edit pages, whilst the bottom two rows control the internal sequencer. The sound editing pages are arranged in a consistent manner, usually with modulation control at the bottom and major parameters at the top of the display. The sequencer buttons are segregated into the five mode buttons on the top row, with the 'tape recorder' type sequencer transport controls sensibly located nearest the keyboard and the player's right hand.

The pitch and modulation wheels are in the traditional place, to the left of the keyboard. The pitch bend wheel is perhaps a bit stiff, although the springing is fine. Both wheels had shallow narrow ribbing, very reminiscent of the original Yamaha DX7, which are not as easy to grip as the broad and deeply ribbed wheels on my SY77. Even so, give me wheels rather than joysticks any day!

The DPM3 user interface has a few dark alleys, which is not surprising given all the black controls! For example, when you wish to return to a page after making a brief excursion to another page, the machine has forgotten which parameter you were editing, and even which page you were on. This can make finding out what the current program is a matter of scanning through all 10 pages before you find the cryptic '>' symbol used to indicate the currently selected program. Minor gripes apart, the DPM utilises plenty of dedicated buttons instead of multi-function ones, and it does not take too long to become familiar with and in control of the instrument.

EXTERIOR VIEW



There really is quite a lot of metal in the DPM3 - virtually the whole of the lower half of the casing is black anodised aluminium extrusion or black painted steel plate. I can remember lugging Peavey combos around in my days as a roadie, and the DPM3 seems to carry on the heavyweight tradition of rugged solidity at 32 pounds (14.5kg). It might therefore come as a considerable surprise when I tell you that the top half is almost all plastic! The front panel is flimsy enough to depress the keys at one end of the keyboard when you lean on it - definitely a case for another piece of aluminium extrusion, I would have thought. Apart from this one problem, the design should protect the keyboard and there are no protruding knobs or switches waiting to be sheared off.

Peavey say that the front panel is actually reinforced with metal, and the removal of two bolts opened up the hinged front panel to verify this. I do not recommend undoing the two front panel access bolts hidden at the bottom of the two large holes in the base plate - it is too easy to lose them inside the machine unless you use a magnetised screwdriver.

The rear panel sockets are recessed into the semicircular extrusions which give the DPM3 its characteristic shape, and this makes them awkward to reach from the front, although it does protect the connectors. Worse still, there is no lettering along the top edge of the front panel to identify the rear sockets, which makes connecting cables a nuisance unless you can get behind and below the instrument. Considering this is Peavey's first attempt at making a synthesizer, this is just about forgiveable.

The left side of the rear panel sports a stereo headphone socket with a separate rotary volume control (the DPM3's amplifier seems much more powerful than most other instruments - be warned!) and the two stereo output jacks, with the left channel doubling as the mono-only output. The output levels are 2V/+6dBV, and a noise gate keeps the quiescent noise floor down to -100dB or better, according to Peavey. The DAC is a conventional 16-bit device which is specified for better than 90dB signal-to-noise ratio, although I did not measure this. The sample rate of the DAC is 39.5kHz, which - for all practical purposes - should give an output bandwidth indistinguishable from the 44.1 or 48kHz rate used for consumer digital audio.

The centre set of sockets provide a control voltage input for a pedal, and three footswitch inputs which are individually assignable to sustain, edit, and program change functions. One of the two sockets accepts standard footswitches, whilst the other accepts a stereo jack from a dual footswitch like the Peavey 710340 dual control pedal. MIDI In, Out, and Thru sockets are also here.

The final set of rear panel connections are on the right, and comprise the mains switch, fuse, and the IEC mains power inlet (a moulded plug lead is supplied with the DPM3). The instrument was supplied configured for 240 volt operation.


VOICE ARCHITECTURE



The DPM3 employs what Peavey describe as 'Digital Phase Modulation', with no further explanation! Looking at what is actually happening inside the synthesis method reveals that the DPM3 is actually a sample playback, or sample+synthesizer (S+S), instrument like the Roland D50 and Korg M1. In the DPM3, the sample playback produces raw sounds or waveforms which are then processed in the same way as an analogue synthesizer, with a filter providing tonal (timbre) control and envelopes providing level control. Stereo panning and digital effects processing complete the sound's route to the outside world.

In these days, where state of the art digital synthesizers look more and more like the analogue synthesizers of old, it is interesting to note that the DPM3 uses a voice architecture comparable to the most sophisticated analogue synthesizers: the two oscillators have their own Digitally Controlled Amplifiers (DCAs) to give mixing and envelope control before the filter, which is followed by a dedicated Volume DCA and Envelope, and then to the output stage. The two oscillators are completely independent in terms of pitch, keyboard tracking or scaling, and modulation. Coarse tuning over 48 semitones (+/—24) and fine tuning provide basic pitch control, whilst the wave sample provides control over the basic timbre of the oscillator.

There are 105 wave samples stored permanently in ROM, although you can load in new wave samples into the DPM3's sample RAM, directly from the (Atari ST compatible) 3.5" disk drive or via MIDI and the Sample Dump Standard (although going by other implementations of the SDS, you may encounter problems with looping). Modulation is described below in detail. Having two sources of wave samples like this means that you do not need to 'double' voices in order to create detuned or parallel sounds, which helps make the most of the 16-note polyphony.

The filter is a low-pass, resonant digital filter where the cutoff frequency is the controlled and modulated (see below) parameter. The resonance alters the response so that it changes from low-pass to narrow band-pass, but this cannot be modulated. Resonant low-pass filters like this one can provide many of the 'classic' swept filter analogue synth sounds, and in conjunction with sampling technology represent a powerful combination.

The output section controls the overall sound level of the program and the panning, again with the standard modulation provisions (see below). Strangely, the pitch wheel range is set here (+/—5 semitones) instead of with the oscillator parameters. The output signal is routed to three places: the 'dry' signal goes straight to the audio output, the first of the two multi-effects processors, or the effects bus which connects to the second multi-effects processor.

The modulation sources and controls are comprehensive, very much in the same style as Oberheim Matrix or Ensoniq synthesizers. You can select two different sources and scale them either positively or negatively - so velocity can be used to increase or decrease parameters like pitch or filter cutoff, and by scaling the keyboard note number you can produce normal and reversed scalings which can help to make the most of the less strongly pitched wave samples. There are 13 modulation sources: four envelopes, two LFOs, keyboard note number, velocity, aftertouch, modulation wheel, an external control voltage pedal, and a MIDI controller (which can also be the data entry slider on the front panel).

The LFOs and envelopes can in turn be modulated by other modulators. The LFO rate can be controlled by only one modulator, whilst the depth can be controlled by the usual two. Five LFO waveforms are provided: triangle, sawtooth (down), ramp (actually an upward sawtooth), square, and random.

The envelopes have four time and five level stages. The levels can be globally controlled by velocity or keyboard note number, whilst the release time can be modulated only by the keyboard note number and the attack time by the attack velocity.

DRUMS & PERCUSSION



Like most keyboards on the market today, the DPM3 offers internal drum sounds as well as its more traditional synth and instrument sounds. If you select a drum sound as the wave sample for an oscillator, then the voice changes its architecture and provides a restricted set of facilities in exchange for allowing up to 32 different wave samples across the keyboard range. Only Oscillator 1 is active, so you cannot generate composite drum sounds by mixing two different drums together, as on the Kawai K4. These changes are not reflected in the voice edit pages so, for example, you can still alter Oscillator 2 parameters, although they will not affect the drum sound.

The most interesting thing about the drums is that they do actually retain much of the flexibility and editing capability of the ordinary synthesizer sounds, which is not the case for most other workstations. Drums often look like a last minute addition, but the DPM3 integrates them into the actual synthesis method and this, coupled with the option of loading in other sampled drum sounds, makes this a potentially 'giant beating' instrument.

MULTI-EFFECTS



The DPM3 contains two digital multi-effects processors, each of which can perform up to two effects simultaneously. Effects processor 1 has stereo inputs and outputs, with their own wet/dry mix control, while processor 2 has a mono input from the effects bus and produces stereo outputs. The first processor can be configured so that the two effects are in series, in parallel, or in a mode which processes the two channels separately. The second processor is fixed in series mode. Seven basic types of effect are available:

- Reverb
- Delay
- Chorus/Flange
- EQ
- Gated Reverb
- Distortion
- Exciter

These can be connected in various combinations, although some are indicated in the LCD screen as 'invalid' when too much processing power or memory is required - typically long delays, reverbs, or chorus. In total, 39 different effects combinations are available. You can edit parameters and name your effects setups, then map these to individual programs. The multi-effects are versatile and behave as if they are separate external units rather than on-board devices.

The multi-effects can operate in four modes: Local Program maps the effects to a program number; Sequencer mode ties the effects to a particular sequence; Global frees the effects from the program or sequence so that you can set a reverb treatment, say, which will remain the same even if you change to a different sound; and Auto selects the correct effect from either the sequence or the program, which is how you normally want it when you are moving between the sequencer and normal playing.

The combination of two effects processors, each able to generate up to two effects at once, is powerful and takes some getting used to. There is certainly no lack of potential here for the creative programmer! The effects themselves are reasonable and of good quality, especially the chorus, but I was particularly disappointed with the reverb - it seemed to be more like a short delay with a few taps and a weird slow attack envelope rather than a dense, crisp reverb.

MIDI MATTERS



The DPM3 dynamically allocates its 16 voices to sounds, and this cannot be overridden by the user. Thus there is no means to reserve voices so that notes are not stolen from important sounds if the 16-note polyphony is exceeded. MIDI overflow is provided, which means that the 4-note polyphony of the complex multi sounds can be increased with another DPM3 or even another MIDI instrument.

The DPM3 has three modes of operation: Omni (MIDI Mode 1), Poly (MIDI Mode 3) and Multi (MIDI Mode 3). Poly works as a 16-note polyphonic instrument on one MIDI channel and Multi is the multitimbral mode, where up to 16 programs on 16 MIDI channels can be set up. The manual refers to Multi mode as "MIDI Mode 4", which it is not! MIDI Mode 4 is actually a Mono mode, which assigns monophonic channels up to the polyphony selected, and is often used by guitar synthesizers. Multi mode contains just one setting, so if you intend to define several multis you will need to store and recall them from disk.

Unusually for an instrument which is probably going to be the centre of a system, you can filter out incoming MIDI messages so that you only receive particular types of message. The master keyboard role is reinforced by the use of the multis to send out four channels-worth of zones simultaneously, and local control can be turned on or off so that you can use an external sequencer instead of the internal one to trigger the sounds.

9-TRACK SEQUENCER



Just like the better workstations, the DPM3 lets you play around with the sequencing, the multitimbrality, and the sound editing in a far more interactive way than would be possible using a separate sequencer. Although it has several details which make it slightly unusual in its class, the internal 9-track sequencer is a reasonably typical 'try out a few song ideas' type.

On the plus side, the sequencer memory is not shared with anything else and it is battery-backed, which means that your hard work does not disappear when you power the machine down (Yamaha SY77 owners turn green with envy at this point!). Even better, you can name sequences and build up a 'pool' of 50 which can be chained together into 10 songs, whereas most other onboard sequencers seem to be cursed with a single song mentality. The patterns aren't really patterns at all, since they are just sequences played on tracks, whereas a traditional pattern spans tracks.

Everything else follows the standard way of doing things. I don't think it is sensible to bore you with the details of recording, transposing, erasing, overdubbing, quantising, copying, or velocity-scaling tracks or parts of tracks. They are all here and work as you would expect. Unlike most other workstations, Peavey's intention to provide updates and new operating systems means that the sequencer could be altered and improved as time goes by, which is a welcome change from the normal situation with hardware sequencers.

20,000 events and 96 pulses per quarter-note resolution is quite generous for a workstation, especially given the ability to quantise during playback without actually affecting the stored information. Step-time and real-time recording of sequences are both possible. All in all, the DPM3's sequencer provides a convenient way to try out musical ideas rather than compose a complete masterpiece. Missing features like the lack of any detailed event editing and control over embedding program changes mean that this sequencer isn't really suited to the more technical or demanding user - but then that's what the sophisticated software sequencers are for...

INTERNAL INSPECTION



I make a point of always looking inside an instrument when I review it. The hidden side of a product can help you to fully understand a manufacturer's attitude and approach in ways that no hype or publicity can disguise. For example, the inside of the DPM3 is neat, tidy, carefully designed, and uses a combination of American and European semiconductor technologies.

Part of the main power supply looks like a conventional linear design, providing +/-15 volts for the small section of analogue circuitry, and +5 volts for the digital circuitry. The incoming mains is filtered at the IEC socket, and a separate 1A fuse and single pole switch complete the input side. Like many pieces of electronic equipment, there are exposed mains voltages inside the unit, so you really do need to know what you are doing before attempting to open it. Leave well alone.

Apart from the two printed circuit boards (PCBs) which hold all the switches and other front panel components, there are only three PCBs inside the DPM3. The Output board is single-sided and has its own regulators to produce the +/-5 volts for the multiplexed Burr-Brown PCM56P 16-bit DAC. Two RCA 4053 CMOS electronic switches are used for the two channel output storage and the five Texas Instruments TL072 low noise op-amps form the output reconstruction filters, along with 12 discrete transistors!

The DSP (digital signal processor) board is a sophisticated, multi-layer, plated-through hole, solder resist board with many of the smaller 74HC series TTL chips being surface-mounted. The board is dominated by the three white ceramic Motorola 56001 DSP chips in their 88-pin packages, running at a crystal-derived 27MHz clock rate. Two of these are used for the oscillators, and the third deals with the multi-effects. The main control processor is a 16-bit Motorola 68000 (as found in the Atari ST, Apple Macintosh SE, and Commodore Amiga computers) running at 16MHz from a second crystal. Connected to the 68000 bus are three 6850 serial communications chips (presumably one for MIDI, one for the serial DAC, and one for general use) and the familiar Western Digital WD1772 floppy disk controller chip, which has appeared in just about every disk drive based device I have reviewed in the past few years.

The memory for the main board is provided by four 62256 32Kbyte static RAM chips, giving 128K in total, with the operating system software held in two AMD 27C512 EPROMs. All the memory is backed up by a rechargeable NiCad battery on this board, and so regular power-ups may be necessary to maintain the integrity of the sequences and RAM samples. You should, of course, save everything to disk regularly anyway.

An Intel 8-bit microcontroller handles the keyboard scanning. Peavey mention an additional 8-bit microprocessor, which I assume is mounted on the front panel PCB and is used to digitise the output of the two pressure sensors mounted beneath the keyboard. I wonder if a future software update will make use of the two zones of pressure sensing?

The Memory board contains lots of 74HCT series TTL chips, all made by RCA, as well as the eight TC534000 ROM chips which contain the two MWords of fixed wave samples, which are expandable to 16 MWords (probably by replacing the PCB, because these are the only ICs that are soldered in; all the rest are socketed for ease of servicing). Two 43256 static RAMs are present in two of the four RAM sockets, which are designed to take either two additional 43256, to give 64KWords of sample RAM, or four larger capacity RAMs to give a total of 256 KWords of sample storage.

The PCBs are mounted on the metal baseplate of the DPM3, and the keyboard needs to be removed in order to get at the RAM and EPROMs, so any upgrades are going to be a job for an authorised service centre, not DIY! I was impressed with the ruggedness of the construction, and especially the lack of any pots or trimmers - if a design is right, it should not need to be tweaked!

INSTRUCTION MANUAL



The manual is American A4 size and has about 150 comb-bound pages. Although produced on a Macintosh, it is poorly laid out, has no index, and quite often wastes a lot of words saying very little. There are very few tables, menu maps and other guides to the user, and this, combined with the tutorial approach, makes it a difficult-to-use reference.

SOUNDS



The sounds are broad in scope, from analogue synth emulations through to glassy modern pads, with some digital textures and unusual sound effects thrown in. A slight American accent is certainly noticeable amongst the sounds, but this adds character rather than detracting. The realism of imitative sounds was not outstanding, and the real strength of the present voices lies with hybrid analogue/digital sounds with elements of both synthesis and sampling.

One backup disk of the factory sounds (100 in total), samples, and demo sequences comes with the instrument, and these should cover the majority of people's requirements. Peavey are actively working on additional sounds, including some European ones. Given Peavey's excellent reputation at home and abroad, third party support for the DPM3 is likely to be considerable.

CONCLUSION



A lot of thought has obviously gone into the design of this instrument, and it shows. The DPM3 does not feel much like the initial release from a manufacturer entering virgin territory, more like an established 'old boy' trying out a few ideas and getting some right and some wrong. (Rather like Yamaha's release of the YS100 and YS200 a couple of years ago.) If Peavey can get the design almost right the very first time, think what they are capable of the next time!

The combination of a lookalike analogue synth voice structure, comprehensive modulation facilities, and wave sample RAM which can be loaded from disk or from samplers, give the DPM3 several advantages over the competition - and the £1899 price tag makes the Korg T3 (plus sample RAM board) look expensive. Since Peavey's intention is to provide upgrades to the DPM3 operating system software, this is one instrument which should not be 'obsolete' as soon as you get it out of the box. The DPM3 would suit the discerning connoisseur who wants an instrument that can sound like the popular machine of the moment but with an extra helping of individuality, long useful life, and flexibility.

FURTHER INFORMATION

DPM3 £1899 inc VAT.

Peavey Electronics (UK) Ltd, (Contact Details).

PEAVEY DPM3 FEATURES

  • Keyboard: 5 octaves, C to C, weighted, attack velocity and aftertouch (channel pressure) sensitive.
  • Voice Architecture: 2 Oscillators, 2 DCAs, 3 general purpose Envelopes, 1 coupled Envelope and DCA. 2 LFOs, 1 low-pass Resonant Filter, 2 Modulation controls per Osc, DCA etc. Orthogonal and often bipolar modulation routings. Drum voice architecture is similar but only 1 Oscillator and fewer parameters.
  • Memory: (1 Word = 16 Bits = 2 Bytes) 2 MWords wave sample ROM (up to 16MW max), 32kWords sample RAM (up to 256 kWords max). Independent sequencer RAM. All RAM is battery-backed.
  • Polyphony: 16-note with Dynamic Voice Allocation (DVA).
  • Storage: 100 single/multi programs (patches).
  • Multitimbrality: 1 setup covering 16 voices/channels.
  • Zoning: 4 zone/4 channel master keyboard facility.
  • MIDI: MIDI Data Recorder (MDR) facility using disk drive. MIDI Overflow mode.
  • Samples: saves/loads 16-bit sample waves in MIDI Sample Dump Standard (SDS).
  • Disk Drive: 3.5" 720K capacity DS/DD disk drive (Atari/MSDOS format).
  • Drums: 5 drum kits with up to 32 wave samples per kit.
  • Sequencer: 96 ppqn, 20,000 event capacity, 9 independent tracks, real/step-time recording. Based on track sequences which can be built up into 10 songs; maximum of 75 sequences with up to 99 repeats per song. Tape recorder emulation, with transport control buttons.
  • Effects: two internal multi-effects units, capable of four simultaneous effects; choice of 39 effect programs.


MULTIPLEXED DACS

In most reviews which look inside any instrument based upon sampling technology, like the DPM3, the phrase 'Multiplexed DACs' appears with monotonous regularity. The Digital-to-Analogue Convertor (DAC) converts from the digital representation to the analogue audio signal, so what does the 'multiplexing' part mean?

The key here is the number of output channels and the number of DACs. Usually there is only one DAC used but two or more outputs. For example, the Roland D110 produces all six of its audio outputs with one DAC! The principle used depends on the fact that most DACs can work at much higher speeds than the sample rate. So suppose that the sampling rate is 44.1kHz, the same as the compact disc (CD) rate, and that the DAC can work at about 100kHz. In this case we could do two conversions and still have some time left, since two lots of 44.1kHz is still less than the 100kHz. This is exactly what the multiplexing involves. The DAC is used to convert first one set of data for one output, and then another set for the next output, and so on.

In a stereo system, one channel is stored whilst the other is converted, and vice-versa. The end result is a DAC which is shared between the channels, and this is exactly what is happening inside the Peavey DPM3. The Burr-Brown PCM56P DAC receives 16 bits of data for the left channel and converts it to an analogue signal. This is then stored in the circuitry around the 4053 CMOS transmission gate whilst it loads and converts the right channel data. The right channel is then stored whilst the next 16 bits of left channel data are processed. It is a bit like juggling - only one ball needs to be manipulated at once because the other is in the air.

In CD systems, high audio specifications are the order of the day, and so separate DACs are often utilised so that the two channels are dealt with by completely separate circuitry. This keeps the left and right channels well separated and gives good stereo imaging, whereas in most musical instruments the two channels often have a lot in common and it makes little sense to try and keep them apart. Using two DACs also ensures that the two channels of audio information are output at exactly the same time, whereas with a multiplexed system there can be a slight time (phase) difference.

What this all means is that for the best audio quality, you should look for instruments which boast the same number of DACs as outputs. In fact, one of the classic customisation jobs to perform on a sampled instrument is to replace any multiplexed DACs with one per channel.


ABOUT THE MOTOROLA 56001 DSP CHIP

The three Digital Signal Processing (DSP) chips inside the Peavey DPM3 do the majority of the hard work in providing the sound of the instrument. Two DSPs are used for the two Oscillators, DCAs and Filter, whilst the third is used to produce the multi-effects programs. There are three other microprocessor chips inside as well, so why all this fuss about the DSPs?

The Motorola 56001 is a state of the art single chip digital microprocessor designed for use with signal processing - hence the DSP tag. Unlike an ordinary microprocessor, it has an internal architecture which is specifically designed to cope with the demands of high precision and very fast speed needed to cope with the mathematical algorithms used to implement signal processing digitally. So, instead of doing multiplication by adding repeatedly, a dedicated multiplier works out a 24x24-bit multiply in a single clock cycle: about 38 nanoseconds (or 27 million multiplies in a single second). An ordinary microprocessor such as the Motorola 68000 (used in the Atari ST, Commodore Amiga, and Apple Macintosh Plus/SE range of computers) can only manage about 27 thousand multiplies in a second.

The 56001 DSP also executes operations in parallel. Whilst doing a multiply, it can also be doing things like loading up values for the next multiply, sending data in or out of its ports, or moving data to or from memory. Conventional microprocessors are typically designed to carry out just one task at a time. The price to be paid for this speed and parallel operation is that you have to plan out your actions very carefully (rather like juggling, since you need to think several moves ahead all the time) and you need to program in a very primitive programming language that has only a few instructions, eg. telling the DSP to move a value from memory to a register, then multiply it, then put it back in memory, etc.

So the programming may be tedious, but where's the harm in that. Well, the major headache is that the mathematical language used to create digital oscillators and filters is much more complex than moving data around in memory. Converting between the mathematical representation and the 'do this, do that' DSP world can be slow, tedious and very hard work, which is why good DSP programmers are well paid and extremely rare!


WAVE SAMPLES

KEY: L = Looped, M = Multi-sampled (obtained by listening!)

Cyclic Loops (single cycle 'basic' waveforms)
01 Sine (L)
02 Triangle (L)
03 Sawtooth (L)
04 Square (L)
05 25% Pulse (L)
06 20% Pulse (L)
07 15% Pulse (L)
08 10% Pulse (L)
09 5% Pulse (L)
10 Digital Wave 1 (L)
11 Digital Wave 2 (L)
12 Digital Wave 3 (L)
13 Digital Wave 4 (L)
14 Digital Wave 5 (L)
15 Pitched Noise Spectrum 1 (L)
16 Pitched Noise Spectrum 2 (L)
17 Pitched Noise Spectrum 3 (L)
18 Pitched Noise Spectrum 4 (L)
19 Pitched Noise Spectrum 5 (L)

Extended Looped Attacks (attack transient plus looped sustain)
(three rhythmic composites of several samples)
20 B Loop (L)
21 C Loop (L)
22 ABCHR(L)
23 Koto tremolo (L)
24 Pipe Organ (L)
25 Full B3 Organ (L)
26 Jazz B3 Organ (L)
27 Organ 1 (L)
28 Organ 2 (L)
29 Percussive Harmonics (L)
30 Bell 1 (L)
31 Bell 2 (L)
32 Fingered Bass (L)
33 Picked Bass (L)
34 Fretless Bass (L)
35 Slap Bass (L)
36 Acoustic Bass (L)
37 Synth Bass 1 (L)
38 Synth Bass 2 (L)
39 Synth Bass 3 (L)
40 Synth Bass 4 (L)
41 Piano (L) (M)
42 Electric Piano Loop (L)
43 Electric Piano 1 (L) (M)
44 Electric Piano 2 (DX?) (L)
45 Electric Piano 3 (DX?) (L) (M)
46 Electric Piano 4 (L)
47 Harpsichord (L) (M)
48 Acoustic Guitar (L)
49 Electric Guitar 1 (L) (M)
50 Distorted Electric Guitar (L) (M)
51 Plucked Electric Guitar (L)
52 Guitar Loop (L) (M)
53 Strings (L) (M)
55 Abbey (Voices) (L)
56 Male Voices (L)
60 Steam (L)
61 Blown Bottle (L)
62 Flute 1 (L)
63 Flute 2 (L)
64 Clarinet (L)
65 Oboe (L)
66 Saxophone (L) (M)
67 Trumpet (L)
68 Trombone (L)
69 Synth Brass (L)
70 Woody (L)
71 Metal (L)
72 Vibes (L)

Extended Dynamic Transients (attack transients and decays, with no looping)
54 Orchestral Hit
57 Squeezebox
58 Lining (Metal Clunk)
59 Breath
73 Tom 1
74 Tom 2
75 Conga
76 Timbales
77 Taiko
78 Gamelan Bongo
79 Gamelan Bells
80 Kalimba
81 Agogo
82 Cowbell
83 Claves
84 Tambourine
85 Cabasa
86 Claps
87 Triangle
88 Pole
89 Scratch Sound
90 Hi-Hat Closed
91 Hi-Hat Open
92 Ride Cymbal
93 Crash Cymbal
94 Reverse Cymbal
95 Electric Tom
96 Kick 1
97 Kick 2
98 Kick 3
99 Kick 4
100 Kick5
101 Snare 1
102 Snare 2
103 Snare 3
104 Snare 4
105 Stick (Rim?)

Specials (multiple tunings, pitch offsets, and keyboard placements)
106 Drum Kit 1
107 Drum Kit 2
108 Drum Kit 3
109 Drum Kit 4
110 Drum Kit 5
111 RAM Sample 1 (L) (M)
... ditto...
... ditto...
143 RAM Sample 32 (L) (M)

The names and the wave samples themselves suggest that these are not exactly 'raw' samples, but carefully chosen and edited samples processed to maximise their sonic potential. Certainly the sound quality is uniformly good, with clear, sharp sounds, and low levels of noise and distortion. There are only a few minor weaknesses: the Piano sample has a decay which is a bit too fast for my taste and this is reflected in the 'Piano' factory voice; the 'Pole' wave suffers from a couple of clicks near its beginning; the looped 'Metal' and 'Vibes' sounds loop at a very quiet level.

The wide range of samples available on the DPM3 enables close emulations of other popular 'sample+synth' instruments, and this is helped by some of the samples themselves. For instance, the 'Pole' sample sounds very similar to the Korg M1 multisound of the same name, and at least one wave sounds remarkably like a Roland D50.


FLEXIBILITY: DSP VERSUS ASIC

Most other synthesizer manufacturers do not use off-the-shelf DSP chips like the Motorola 56001, so why have Peavey chosen to do it this way?

The traditional way to implement signal processing in digital synthesizers is to use Application Specific Integrated Circuits (ASICs). As their name suggests, these are chips which are designed to do one thing only, for a particular purpose, and they will do this efficiently and quickly. To achieve something different, you manufacture a new ASIC. Many of today's consumer products are full of them: compact disc players, video recorders, etc.

The advantage of an ASIC is that you can manufacture it cheaply in large quantities and it does exactly what you want. Also, no other company can use it, since it is available only to the people who designed it. In contrast, anyone can buy and use Motorola 56001 DSP chips, since they are general purpose devices which can be applied to a wide range of tasks - it is the programming which determines what they will do. It is this flexibility which Peavey are aiming to exploit with the DPM3.

The hardware for most of today's hi-tech instruments is very similar, and the DPM3 takes the hardware and puts three DSPs at the heart of it, instead of designing dedicated ASICs to perform a specific task and then building the hardware around them. If you reprogram the DSPs then you have a different instrument, whereas no manufacturer is ever going to go to the expense of changing an ASIC.

The DPM3 is currently configured so that it behaves like a sample+synth (S+S) instrument, but by changing the DSP programs it could be turned into an FM synth (Peavey are rumoured to be working on this), or an Additive synth, or the current implementation could be improved and extended in ways that no ordinary software update could achieve on a conventional instrument. This is why Peavey believe that the DPM3 is not going to be made obsolete until the basic hardware has been superceded. Peavey (and possibly third party companies?) can keep improving and upgrading the DSP software to suit whatever synthesis method is in vogue. The limiting factors on the life of the instrument will be the 16-bit precision of the digital-to-analogue convertor (DAC) chip, the size of the sample memory within the DMP3, and the complexity of the processing required to achieve future synthesis methods.

A reasonable analogy is the difference between a DX7 and a Synclavier. The DX7 used ASICs to do its signal processing, whilst the Synclavier uses DSP-type technology. The DX7 was burned out, 'obsolete', and unfashionable after five years, whereas the Synclavier is just as desirable now as it was 10 years ago. It is the re-programmability (the software) that keeps the Synclavier in its preeminent position. The basic hardware of both instruments has a high enough specification to cope with sufficient bits of resolution at a suitably high sample rate to give excellent audio quality, and the human ear is unlikely to change its characteristics in the near future!



Previous Article in this issue

Studer Dyaxis

Next article in this issue

Hybrid Arts SMPTETRACK II


Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

 

Sound On Sound - May 1990

Donated by: Bert Jansch / Adam Jansch

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Gear in this article:

Synthesizer > Peavey > DPM3


Gear Tags:

Digital Synth
Polysynth

Review by Martin Russ

Previous article in this issue:

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> Hybrid Arts SMPTETRACK II


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