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Akai DPS24

24-track/96kHz Digital Studio
Published May 2002
By Hugh Robjohns

Akai's new 24-track recording and mixing workstation continues the expansion of their DPS multitracker concept with technology derived from the company's renowned post-production machines.

The concept of the digital multitracker is a very familiar one these days, with many impressive offerings from all the major manufacturers — Yamaha, Roland, Korg, Tascam, Akai, and one or two others — with models spanning a fairly broad price range. Akai's latest addition to the genre builds upon the company's existing DPS12 and DPS16 models, but also incorporates quite a lot of technology derived directly from Akai's range of professional post-production equipment. The new DPS24 is designed to be the company's flagship integrated personal studio, with sound quality and ease of use very much at the top of the feature set. In comparison with the products with which it is competing, I think it is fair to say that the DPS24 sits pretty much at the top of the list — partly because of its comprehensive and professional-calibre facilities, but also because its relatively high recommended retail price forces it into that position.

AKAI DPS24 digital multitracker. Photo: Mark EwingThe DPS24 shares the now almost universal styling of this kind of product, with a typical assignable mixer section to the left, transport controls to the right, system function keys in the centre and a monochrome LCD screen above. The LCD is unusual in that its angle can be adjusted mechanically to improve visibility. Another unusual aspect is that, in addition to the common operational paradigm of six soft function keys along the lower edge of the screen (the functions of which change to suit the menu page being viewed), there are also six Q-Link encoder knobs along the right-hand edge. These are used to adjust various parameter values, their function changing with the different menu screens much like the soft keys. This concept works extremely well and makes the DPS24 very easy, fast, and obvious to use. It also allows multiple parameters to be changed simultaneously — a rare feature on even mid-price digital desks.

The machine's 24-track digital hard disk recorder employs only linear (ie. not data compressed) 16-bit or 24-bit audio files, but at any of the standard sample rates between 32 and 96kHz. Another very welcome but highly unusual point here is that you don't lose half the machine's capabilities when operating at 96kHz either! There is more than enough DSP to enable full functionality at any of the sample rate options.

As I have already mentioned, much of the recorder's technology has been derived from Akai's other professional audio products, including some excellent editing features which owe much to the DD series of post-production recorders and editors. Indeed, the editing functions on this machine are easily the best I have come across on any digital personal studio — not so much in terms of basic functionality, but certainly in terms of ease of use and clarity of display. All editing functions are non-destructive with a comprehensive set of tools including all the usual cut, copy, paste, erase, and insert functions, plus multiple undo/redo options and superb tape-style scrubbing (across all 24 tracks when required) to fine tune edit points.

The system also provides up to 256 virtual tracks which can be swapped for the playback tracks whenever required. Essentially, the hard disk supports direct record and play access with 24 separate audio tracks at a time, but up to 280 tracks of material can be managed within any one project. This makes it possible, for example, to record multiple takes of a vocalist on different virtual tracks, and then compile and edit a composite track from these, bouncing the result back onto a new track ready for the mixdown.

A similar technique is used to create a master stereo mixdown of a project. The stereo mix is recorded onto a pair of virtual tracks and after 'topping and tailing' these are subsequently copied to the internal CD-RW drive to compile a Red Book compatible CD-R. There is a library of preset routing configurations available within the machine to simplify these kinds of operations, too.

Hardware Interfacing

The DPS24 has been designed with sufficient interconnectivity as standard to allow trouble-free interfacing for the vast majority of potential users. There is plenty of analogue I/O (particularly inputs), plus eight-channel ADAT and stereo S/PDIF digital connectors. In addition there is provision for up to three expansion cards, of which a couple are currently available: a dual ADAT board (providing a further 16 channels of ADAT optical I/O interfacing plus an ADAT Sync socket, to supplement the onboard facilities) and an EBU/SMPTE timecode reader/generator card. Presumably Akai will eventually develop TDIF and AES digital card options too, although this may depend to some extent on user feedback — the ADAT lightpipe is clearly the most universally employed multi-channel digital format at present.

In addition to the three expansion card slots, there is also an optional SCSI interface board for the machine, which is currently only usable for data backup. Apparently a future software update may also enable the possibility of recording and replaying in real time from suitable external SCSI drives — which would be a very useful facility and a significant advantage over some of the competition.

Returning to the analogue side, there are 12 mic/line input stages in the machine, each with two selectable input connectors — a combi jack/XLR socket and a TRS jack socket. This arrangement helps to minimise the need for source replugging, since both inputs can be left connected to instruments, samplers, and other equipment, and then selected when required. The first four channels' combi-XLR sockets are also equipped with a common 48V phantom power supply (switched globally), as well as separate balanced insert send and receive sockets.

The mic amps sounded pretty quiet and clean overall, although there was a noticeable peak in the noise level when the gain control was around the two-o'clock position, and again when the control was approaching flat out. Overall though, there was plenty of gain available (over 70dB with the faders at maximum) and it all sounded very good indeed. High-quality external mic amps would have the edge, but would be far from necessary with the DPS24. Channel 12 offers the extra feature of a high-impedance 1MΩ jack input mounted on the front edge. This is a break jack, so plugging in a guitar or bass disables both rear panel inputs to channel 12.

AKAI DPS24 rear connections.Photo: Mark EwingOther analogue inputs on the machine include unbalanced phono sockets for a two-track tape machine return, which can accommodate both +4dBu and -10dBV nominal signal levels thanks to a setup menu in which the sensitivity and gain can be adjusted as necessary. There is also a stereo auxiliary input via balanced TRS jack sockets which is intended to introduce the output from a separate mixer directly to the main mix buss of the DPS24 — although it can be routed to almost anywhere else in the desk via the internal mixer routing.

The stereo S/PDIF interface is provided on phono connectors, although the ADAT optical port can also be reconfigured to carry stereo S/PDIF signals if required. Digital synchronisation is taken care of via a single BNC word clock connector which, rather unusually, can be configured either as a clock input or a clock output. If the machine is running from its internal clock the BNC provides a clock output, but if external clock is selected it can be used to accept the external reference clock signal. Any of the digital inputs (either those built in or those on the option cards) can also be selected as clock sources, of course.

The analogue outputs of the DPS24 are all on balanced TRS jack sockets. There are four aux sends, although these are really more like the Yamaha Omni outputs, as the physical connectors can be assigned to carry more or less any signal from the machine's mixer busses. There is also a dedicated main stereo buss output, and three stereo monitoring feeds: studio monitoring, plus nearfield and main control-room monitors.

The machine is designed to use aux busses three and four to generate the studio monitoring cue feeds. However, these busses must be selected specifically to serve this purpose, rather than as general-purpose auxes. Allocating them to studio-monitoring duties enables them to receive the output of a built-in studio talkback mic facility controlled by a button and volume control just below the LCD screen, which is another nice example of the level of professionalism embodied in this machine.

The control-room monitoring facilities are some of the most comprehensive and usable I have yet come across in a machine of this type. The provision of both main and nearfield control-room stereo monitor speaker feeds is an excellent idea, allowing easy interfacing of 'quality monitors' and 'grot-boxes', for example, which makes comparative mixing a lot easier. The inclusion of a mono switch is also a nice touch, as is the pair of stereo headphone outputs on the front of the machine (with a shared volume control).

At present the control-room monitoring is only stereo capable (with a dual-mono mode for compatibility checking). However, Akai have said they intend to implement some form of surround facility in later versions of the operating system (allegedly from v1.3). If that happens the suggestion is that all six monitoring outputs will be used together to provide a 5.1 monitoring feed for the control room, which would presumably only be required during mixdowns, and the buss record outputs would be accessed through the ADAT port (or other expansion card option).

To complete the facilities, there is the usual trio of MIDI ports along with a USB socket which allows software updates to be sent to the machine (from a PC only at present) and which will eventually be used for a remote display of waveform editing and machine control functions using Akai's AKsys software (which is already used with many of the company's other products). There is also a PS2 keyboard socket to enable easier project and channel naming, although I have to say I had no difficulty at all using the Q-Link controls alongside the LCD screen for the purpose — particularly since the alphanumeric characters have been grouped under different knobs: A-Z, a-z, 0-9, and other characters. There is a speed-proportional aspect to the encoder knobs, so spooling through the alphabet is very fast and easy.

A quarter-inch socket is provided for a footswitch and the system can be programmed to react in a variety of ways to each switch action, including a play-record-play-stop sequence, and a simple punch-in/out mode. It can also be set up to accept remote control instructions from an Alesis LRC — another nice inclusion.

The rear panel of the machine is drilled for a cooling fan and the units I saw at the recent Musikmesse show in Frankfurt (as well as those in the product brochure photographs) were all fitted with temperature-dependent fans. However, the review machine was not equipped with a fan at all. My cynical mind suggests this may have been an attempt to make the machine ultra-quiet for the review, but it didn't appear to become excessively hot, even when left running for over ten hours straight, and showed no signs of stress at all! Maybe the company has discovered that a fan really isn't required, which would be very welcome of course, and it means that only the modest hard-drive whine and chatter has to be suffered. Certainly, I had no problems using the review machine to record acoustic sources in the same room.

Internal CD-RW Drive

The machine also includes — as standard in the UK — a CD-RW drive to allow project backup and restore operations, as well as direct Red Book compatible disc pre-mastering. It is not possible to record a stereo mixdown directly to the CD-RW: as I mentioned earlier, the mixdown tracks have to be recorded onto the hard drive first using virtual tracks. The file can then be copied to the CD-RW to build up a final CD.

The CD drive can also be used to load operating software updates. The handbook recommends downloading these from the Akai web site, burning them onto a CD-R, and then loading them into the machine — a menu screen leads the user through the necessary stages, although care should be taken to avoid trying to update the software if there is any likelihood of a power failure part of the way through the process. As someone who lives in the countryside with overhead power lines, I'm only too familiar with that particular problem!

One rather odd point is that, although the CD drive can be controlled as a CD player through another menu screen, it can only be monitored through its own 3.5mm headphone socket. I could not find a way of loading material from the drive directly onto the DPS24's hard drive via an internal data path. This will come as a major disappointment to anyone wishing to load samples, for example.

Effects Processors

Akai have designed the DPS24 with four aux sends from each channel, but these can be configured to drive 10 different destinations — either globally or on a channel-by-channel basis. There are four conventional aux sends which appear on the rear panel, of which aux three and four can be re-allocated to serve the studio monitoring as already described. There are also four internal effects sends to drive the four onboard mono-in, stereo-out internal effects processors. Their outputs are normalled to four stereo effects returns channels. These can be routed in the usual way, including back out to other auxes, so adding 'performance reverb' to the foldback cue mix is very easy.

Each effects processor offers a wide range of conventional effect algorithms, all with very informative graphic displays and comprehensive adjustable parameters. The options include reverb, delay, chorus, flanging, phasing, pitch-shifting, auto-pan, rotary speaker simulation, distortion, EQ, dynamics, spectral enhancer, and so forth. I found these effects to be good-quality, usable and worthwhile tools — easily on a par with typical mid-budget multi-effects processor boxes. If I were being critical I would say the reverbs seemed a little mechanical and lacked the depth and warmth associated with the likes of Lexicon's and TC Electronic's best efforts, but that would hardly come as a surprise, would it?

If you want to integrate high-quality external effects units with the DPS24, it is easy to route an aux send to an output and to return the processed signal through either the auxiliary stereo input, the two-track return, or a couple of spare channels — whichever is the most convenient. However, there will be a delay issue to contend with, because of the four stages of digital-analogue conversion involved (out of the DPS, into the effects processor, out of the effects unit and back into the DPS). This delay would typically amount to between 4ms and 8ms, depending on the type of converters involved, and might well cause problems with phasing and colouration if significant amounts of the dry signal are returned.

This delay problem can be minimised by avoiding the analogue I/Os completely and reconfiguring the S/PDIF ports to output a suitable aux send, returning the effects signals to an effects return channel. The DPS24's internal routing makes this a simple task, but, as there is only one S/PDIF interface, only one outboard digital effects unit can be interfaced this way.

Also included are a number of off-line effects as well, such as phase-coherent time stretching (with a library of optimised algorithms to suit speech and various music genres), tempo matching, varispeed, normalise, and reverse effects. To use these modes, a section of audio (one or two tracks only) is identified in the editing screen using the conventional In and Out markers, and then the appropriate DSP effect is selected and applied. The processed material is eventually inserted into the selected track(s) to replace the original. The time required to perform the off-line processing obviously depends on the length of the selected material as well as on the nature of the process itself.

Machine Control & Synchronisation

As we have come to expect from Akai, given their experience in the TV and film post-production industries, the DPS24's ability to synchronise to other machines is exemplary. The usual MTC, MMC and MIDI Clock functions are included as standard, but Akai are also offering an optional EBU/SMPTE LTC (longitudinal timecode) interface card to allow precise timecode-locking to external video machines or other timecode-based transports.

The chunky transport controls are laid out logically, and there are a number of button combinations which provide useful extra functions, including a 5x spool speed (complete with audio chattering just like spooling tape against the heads) to aid in locating portions of a recording. There is also a jog/shuttle dial (with an on/off button to disable it if required) which feels very good to use. The audio scrubbing afforded by the jog wheel is excellent — a facility finely honed through generations of Akai's post-production machines — although the slightest touch of the wheel while playing causes the machine to stop immediately and enter the jog mode. This caught me out on several occasions, particularly when reaching for a screen soft key and accidentally brushing against the wheel. It soon becomes clear why Akai felt it necessary to include the jog/shuttle on/off button! The shuttle wheel makes spooling back and forth through a project a breeze, with fine variable speed control.

A better way of working, though, is to set locate markers at the key points throughout a project, and the DPS24 provides up to 100 memory locate points per project. These can be recalled directly by pressing the Goto button followed by the relevant locate number, or by naming each point and selecting from a list. Alternatively, specific timecode points can be typed in.

There are also several buttons within the transport section to determine the way the machine behaves in relation to selected edit points or locate positions. These include Play To, Play From, Play Over, In-Out (play between the In and Out points), and Loop (cycles continuously between the In and Out points). Pressing the Goto button in conjunction with some of the transport controls also provides some handy features, such as Goto + Rewind which relocates to the start of the project.

Mixing Topography

The heart of the DPS24 is clearly its 46-input, eight-group mixer. This is designed to operate in a very traditional way by default, although the actual source for each input channel, group and multitrack input can in fact be derived from any physical input on the machine, (or from an internal metronome). Akai have not included a line-up oscillator function. The complete collection of 46 inputs comprise 12 input channels, 24 disk tracks, four stereo effects returns, and the stereo auxiliary input. There are twenty mix busses: the eight groups, four internal effects sends, four external aux sends, the main stereo bus and a stereo solo-in-place monitoring bus.

The standard default configuration of the mixer is with the 12 input channels receiving signals from their corresponding analogue input stages. The input channels can then be routed either directly to the main outputs or to one of four stereo groups which, in turn, are hard-wired to feed the multitrack recorder's tracks in repeating blocks of eight — much like a conventional analogue multitrack setup. Alternative input configuration presets are also available, such as a direct mode where analogue inputs feed 12 tracks directly.

The multitrack outputs are normalled to their corresponding mixer return channels (on two further fader pages), and the mixer's main stereo output can be dispatched to an external recorder or to the internal hard drive as required. There are also four dedicated stereo channels to return the four internal stereo effects processor outputs to the mix buss.

One particularly nice aspect of the machine is that most routine channel and track assignment, signal processing and recording functions can be controlled entirely from the mixer's front panel without recourse to any LCD screens or menus at all. The control and selection buttons are all illuminated and change colour or provide steady and flashing modes to indicate their status. This is all arranged in such a way that, once familiar, the mixer is very fast to set up and operate, although I have to say I found it initially slightly less intuitive than I was expecting.

DPS24 Automation Facilities

The machine is equipped with a conventional automation system, including both static and dynamic functions. The dynamically automated controls include all the faders, on/off switches, pans and aux/effects sends, while the static facilities also cover things like the EQ, dynamics, and effects processes.

The system uses the first Scene memory as its channel parameter starting point for an automation pass, so keeping that scene memory up to date with the required static controls is paramount to a successful mix. Everything else is reasonably intuitive. You can arm the system to automate effects/aux sends, channel switches, pans and faders individually, or you can record everything at once, and there is a comprehensive 'record safe' mode to prevent automation data from being overwritten on specific channels. There are various drop-out modes too, including an automatic function for when the faders are released. If a pass is stopped, the automation can be set up to revert to the previous parameter values over a preset time, or to hold the new settings until the end of the project. The fader motors can also be disabled if you don't want to see them moving about.

Channel Facilities

The mixer feels very professional and 'grown up' with its 13 touch-sensitive motorised 100mm faders. Each channel has its own assignable encoder knob, On and Select buttons, plus banked track-arming and edit-selection buttons. The faders are allocated to control various channels and functions through five pages. These accommodate the 12 input channels, 24 track returns (1-12 and 13-24), group masters and effects returns, and a user-configurable bank which can be programmed to access various other facilities such as the aux send masters or MIDI messages to control external equipment.

The assignable channel encoder knob defaults to operating as a conventional stereo pan control, but it can also be assigned to adjust the level of each of the four aux sends or four internal effects sends (depending on how the channel is configured). The collet around the base of the knob carries an arc of rectangular orange LEDs to indicate the current setting. There is also a red LED at the bottom centre which illuminates when the parameter is normalised (ie. centre pan, zero EQ gain, and so on) — another thoughtful inclusion.

The orange LEDs are illuminated in different ways depending on the function assigned to the control knob at the time. Panning is indicated by a single LED illuminated at the appropriate position around the control; aux send level is indicated by a growing block of LEDs anchored from the seven-o'clock position; EQ gain is shown by a block of LEDs growing to the left (cut) or right (boost) of top centre; and EQ bandwidth by a block of LEDs which builds symmetrically either side of top centre. The description sounds complex, but it's all perfectly obvious when seen in action.

All of these different display modes come into play when the Q-Channel mode is activated. This handy facility is similar to that used on several other digital consoles, and it reassigns all 12 channel encoder knobs to provide simultaneous access to the principal parameters of any one selected channel. The arrangement provides channel pan, three-band EQ (high and low shelves plus a parametric mid-band) and four effects/aux send controls.

All of the input channels and tape returns are equipped with a useful array of permanent facilities. Aside from the parameters already mentioned, there is also polarity reversal, input attenuation, and metering selection (pre-EQ, pre-fade and post-fade), plus a comprehensive dynamics section with a compressor/expander and separate noise gate. There is no provision for side-chain access to the dynamics, perhaps to allow key control of the gate, for example. Unusually, there is no channel delay facility either.

The dynamics functions are controlled through LCD menus, and there are two dynamics pages per channel (compressor/expander and noise-gate) arranged so that all six parameters in each section can be adjusted directly and simultaneously through the screen's Q-Link controls. Although the pan, EQ and aux settings can be controlled directly through the Q-Channel, they can also be adjusted using the LCD and Q-Link knobs as well, although the arrangement here is that a parameter must be highlighted using the cursor buttons, and then adjusted with the bottom Q-Link control. Although most users will probably stick to the Q-Channel most of the time, I found this alternative mode useful on occasions.

Stereo linking between odd/even channel pairs is performed cleverly. Linking is activated by pressing and holding one channel's Select button followed by that of the adjacent channel in the usual way — but the clever bit is that first channel's settings are copied to the other.

A point worth noting is that although all 12 channel inputs, the 24 track returns and the effects returns have the full complement of pan, EQ, dynamics, and routing facilities, the groups do not. Thus it is not possible to allocate a number of sources to a group to apply overall compression, for example, and you can't easily route a group back to another input channel — only to a record track. You can get around the problem, but it's not pretty...

Conclusions

This is a very well designed personal recording system with more professional features than many of its competitors. It is fast, intuitive, and easy to use, and offers fine technical and operational performance in its current form. However, the system is relatively expensive and its operating system is still at the stage of development where some significant features are not yet available. The DPS24 shows signs of becoming the class-leading machine, but users will have to wait for further software updates before it reaches its true potential.

Published May 2002