Yamaha D24 MO

The eight‑track digital recorder has become a standard building block at virtually every level of the recording industry, and a wide range of tape and hard disk‑based devices is available. Now Yamaha have extended the choice with a machine built around a 640Mb magneto‑optical drive. Hugh Robjohns takes it for a spin...

The concept of the Modular Digital Multitrack or MDM has been widely adopted across the professional and semi‑pro recording industry. It all started back in the early 1990s with Tascam's DTRS and Alesis's ADAT formats. DTRS has become the mainstay within professional circles whereas ADAT reigns supreme in the MI business, and both formats have been adopted by other manufacturers — Sony in the case of DTRS and Studer for ADAT. Both of the original systems have also seen upgrades to higher resolutions recently.

However, ADAT and DTRS are far from being the only MDM formats on the market. It seems that virtually every significant pro audio manufacturer has something similar to offer, and many are based around hard‑disk formats rather than tapes — for example, the DAR, Genex and Akai systems, to name just three. Yamaha have recently joined this competitive marketplace with their own contribution, the D24 Digital Multitrack Recorder.

Mo Moves

The D24 introduces a new multitrack recording medium, the 640Mb MO disk, and yet another proprietary file structure.

This latest eight‑track MDM introduces yet another new recording format, the removable 640Mb magneto‑optical (MO) disk, and uses a completely proprietary disk structure. By using removable disks, Yamaha's design negates the requirement for lengthy backup and restore processes, but the limited capacity of the current MO disk will significantly restrict the applications to which the D24 is suited — at least in its intended form. However, Yamaha have equipped their new machine with a great deal of flexibility, enabling it to be used in many different ways and across a range of disciplines, including project‑studio music recording and certain audio‑for‑video applications.

Like all disk‑based recorders, the D24 offers instant random access to any point within the recorded material, and recordings are organised into projects which may be titled for easier recognition. The audio recording format is uncompressed with 16‑, 20‑ and 24‑bit resolutions and 44.1/48kHz or 88.2/96kHz sample rates. Both standard MO disks and the more recent Direct Overwrite disks are supported (see box): Direct Overwrite MO disks provide eight‑track recording at 44.1/48kHz across all bit resolutions, and four tracks at 88.2/96kHz. Standard MO disks, by contrast, provide only six tracks at 20‑ or 24‑bit resolutions, dropping to three tracks at elevated sample rates! A 640Mb Direct Overwrite disk allows 15 minutes of eight‑track recording at 16‑bit/44.1kHz, decreasing to 10 minutes for 24‑bit/44.1kHz and nine minutes for 24‑bit/48kHz. For the ultimate in fidelity, four tracks of 24‑bit/96kHz will also last nine minutes. Up to 99 projects can be recorded per disk, with sample rate and bit resolution established on a per‑project basis.

The limited capacity of current MO disks inherently restricts the applications in which the D24 can be used — it will be fine for recording one or two music tracks per disk, but of limited use as an audio‑follower in video post‑production! To overcome these limitations, the machine has a SCSI port on the rear panel allowing up to five external hard drives to be connected, increasing substantially the maximum recording time, the internal MO disk effectively becoming a backup medium.

Alternatively, recording capacity can be expanded by interconnecting up to eight D24s to give sample‑accurate 64‑track recording: in this arrangement, word clock and timecode are distributed from the master machine to seven further slave recorders. A serial connection mode can also be used to allow extended recording durations. This mode arranges for a second machine to take over recording at a specific timecode value when the first machine nears the end of its disk capacity. This typically involves allowing a 30‑second overlap between one machine starting and the previous one stopping. Both machines will of course require identical input signals. The D24 supports and generates SMPTE/EBU and MIDI (MTC) timecodes and responds to both standard RS422 serial control protocols (the Sony 9‑pin standard) along with MIDI machine control (MMC).

In addition to the eight physical tracks on the disk, the D24 provides eight 'virtual' tracks for each real one. This provides considerable flexibility, allowing alternative takes to be compared and compiled into the final track. The D24 also provides a solo monitoring function enabling selected tracks to be auditioned in isolation. A comprehensive punch‑in/out system has the ability to repeat punch‑ins for up to 99 takes, each stored pending selection, with a rehearsal mode which switches the monitoring to input on record‑enabled tracks automatically, allowing the timing points to be checked and fine‑tuned before committing with the big red button.

A video‑like shuttle ring control permits audible locating through a track and a cue point can be set precisely to sub‑frame accuracy with the jog dial control. There are 99 locate memories per project, A‑B repeat loops, record in and out points, as well as a user‑defined zero‑locate point and a ±6 percent varispeed facility. There is also a very handy rollback feature: on the press of a button, the project rolls back a user‑defined amount between five and 30 seconds before playing over the section again.

One of the advantages of a disk‑based recording system is the ability to provide non‑destructive editing — not only familiar features such as cut, copy, paste, delete and erase, but also track slipping, the insertion of space, and track swapping. On‑board DSP also allows time compression or expansion (between 50 and 200 percent) and pitch‑shifting (±1 octave). These last processes can be auditioned on‑line but are recorded off‑line.

The machine is fitted with comprehensive synchronisation, timecode and remote‑control interfacing, but only rudimentary audio I/O (a single S/PDIF interface and a headphone socket to be precise). Buyers can configure the audio I/O to their own requirements by installing up to four optional mini YGDAI cards allowing flexible, user‑configurable digital or analogue interfacing.

The Tour

Although labelled 'Analogue In', slots 1 and 2 can also be used for digital I/O cards; slots 3 and 4 have to be used for outputs.

The controls are laid out conventionally, and experience of other eight‑track MDMs will translate easily to the D24. The basic layout is right‑handed with transport controls occupying the right side of the front panel below the disk drive slot. Various setup and utility buttons are located in the centre of the machine above the multi‑function jog/shuttle wheel, and a large fluorescent display dominates the left‑hand side. Associated with this display are the usual track‑select and monitoring buttons, together with a numeric keypad for time and data entry.

The bottom row of large buttons in the transport section are illuminated and provide the usual rewind, wind, stop, play and record functions. The first two buttons in the middle row provide a return‑to‑zero locator and the rollback function (with a cue beep when it enters play). Next are A and B memory buttons, each with a red LED illuminating when a time value has been stored — this is done by simultaneously pressing the SET button in the top row with the appropriate A or B button. The Repeat A‑B button activates this function with a very short gap between the end of the loop and its restart (hence the need for the cue beep). Another red LED warns when the repeat function is active. The last button of the middle row is labelled REHE (better to use the first four letters of 'rehearse' than the last,I suppose!). This enables automatic punch‑ins and ‑outs to be practised and fine‑tuned; once again, a red LED warns when this feature is active.

The first pair of buttons in the top row are used to scroll forwards or backwards through the projects on a disk: the active project is the last one selected. The next pair of buttons operate like the A and B buttons directly below, in conjunction with the adjacent SET button. These buttons store the punch‑in and ‑out points (labelled Rec In and Rec out). The last button activates the Auto Punch mode, again with a red status LED.

The MO drive above these transport controls has an Eject button which doubles up as a disk‑activity light. Yamaha supply a special tool which, in the event of a problem ejecting the disk, can be inserted into a small hole under the disk slot to force a mechanical ejection. To the right of the disk drive and transport controls are a mains power button and a headphone level control and socket. Even‑numbered tracks are allocated to the left headphone channel and odd tracks to the right: individual tracks can be auditioned through the track solo buttons under the metering display.

The multi‑function Jog/Shuttle control at the centre of the panel is used both for transport operations and for data selection and modification. The associated 'Jog On' button (with LED) allows the control to determine the position through a project. The outer shuttle wheel is spring‑loaded and effectively 'spools' the audio material to allow audible cueing. When not selected for transport duties this ring moves the cursor on the various menu displays, for example to select virtual tracks or characters during project titling. The inner Jog dial allows fine time adjustments and scrolling in the transport mode, or selection and modification of selected data in the on‑screen menus.

During certain editing functions — for example, setting time‑compression or pitch‑changing settings — the jog dial allows ultra‑precise adjustment of the relevant parameter to 0.01 accuracy. However, trying to dial in a time‑compression factor of, say, 0.88 (to reduce 34 seconds of track to fit a 30‑second slot) takes several days of twirling to achieve! The relevant value can be entered directly through the keypad, but it would be more intuitive if you could grab the shuttle ring and twist it in the appropriate direction to make the numbers scroll quickly. This is not currently implemented, but as the shuttle ring is not used for anything else in these modes, it would make ergonomic sense if Yamaha updated the control system to provide this additional functionality.

A block of nine buttons above the jog dial provides various utility functions. The bottom row accesses the virtual tracks, edit modes and an undo/redo function to clear or reinstate the last recording or edit. The middle row activates varispeed and accesses the utility and setup menus. The top row is used in conjunction with the time display, capturing the current time for storing in a locate memory, and switching the display between absolute, relative, used or remaining times.

The Edit modes include the copying, erasing and titling of projects; copying, moving, erasing, swapping or slipping complete tracks; and copying, moving, erasing and inserting parts (subsections of tracks). The Edit button also provides access to the time‑compression and pitch‑change functions, the former having three user‑selectable algorithms optimised for vocals, rhythm or general material. Both of these functions can be used on an individual track or pair of tracks — the relevant section is identified via the Rec In and Rec Out points. The processed result is stored as a virtual track(s) which can be moved back to the main track if satisfactory.

The Utility menu allows the user to configure the range of the audio metering (‑60 or ‑26dBFS), rollback time, pre and post‑rolls for the autopunch, edit crossfade durations, and edit‑point nudge amounts. There are also facilities here to select a specific disk (when using external SCSI drives), format new disks and defragment old ones.

The Setup menu establishes the word clock source, timecode source, frame rates, offsets and chase mode (see below), and is also used to handle input source selection. There is, incidentally, a trap concerning the S/PDIF input selection: it overrides any other audio input (ie. the analogue or digital inputs via the YGDAI cards). The problem is that there is no warning of this condition, resulting in a lot of confusion when an input signal selected through a YGDAI card fails to materialise. The operating software really should prevent selection of a Slot 1 or 2 input if the S/PDIF port is already enabled.

The numeric keypad is used to enter specific locate points or data values during menu functions and has associated Cancel and Enter buttons. The latter also accesses selected submenus and confirms parameter changes. The right‑hand column of the keypad contains dedicated buttons to access projects directly by number, store and recall locate memories, and locate to a time value shown on the display (either through capturing a time or by recalling a previously stored memory).

Two rows of buttons below the metering display provide track arming and track solo monitoring, and both features are entirely intuitive. Below these, five further buttons (all with LEDs) enable Peak Hold, switch the monitoring between conventional all‑input and auto‑input modes, and activate chase synchronisation. Another button carries out a high‑level format on the selected disk, in other words erasing the table of contents from previously used D24 disks. Brand‑new disks, or disks not complying with the Yamaha format must be low‑level formatted, a function accessed from the utility menu.

Round The Back

Three of the miniature YDGAI cards used to provide the D24's I/O: (left‑right), the ADAT digital I/O card, the four‑channel D‑A, and the four‑channel A‑D cards.

The rear panel contains a wealth of interfaces, including four slots for optional mini‑YGDAI cards. The top row includes video and word clock interfaces (both with In and Through sockets, plus termination switches), a trio of MIDI sockets, a 50‑pin half‑pitch SCSI port (see SCSI box), an RS422 9‑pin serial port, and a pair of 15‑pin D‑sub sockets labelled Remote/Sync In and Sync Out. These are used to interface the optional remote‑control unit, and also to connect multiple D24s together in various configurations using 15‑pin sync cables.

The lower left quadrant contains a reasonably quiet cooling fan along with the usual IEC mains inlet, timecode In and Out sockets (on XLRs) and a pair of S/PDIF digital I/O connectors. These can be assigned to individual pairs of tracks, all tracks (allocated on a left‑odd, right‑even basis), or turned off completely. The S/PDIF input accepts 16‑, 20‑ or 24‑bit signals, as determined by the current project settings. However, there is no facility to redither 24‑bit input signals if you are recording at 16‑bit, for example, and care must be taken to set the correct dithering options at source. The S/PDIF output resolution is the same as that of the recording, and it is disabled for elevated sample rates.

The D24 supports all the usual timecode formats including 24, 25, 30‑drop and non‑drop frame rates. It contains its own internal timecode generator but can also slave to external timecode or timecode via the Remote/Sync‑In connector, as well as accommodating MIDI Time code (MTC). The synchronising timecode source (internal or external) is also output through the same array of ports, including MTC, and with an offset if required.

Four slave chase modes provide a continuous chase lock, a sync and free‑run operation, and two variations on this last mode which cause the transport to stop if the code becomes unreadable for either 1 or 2 seconds. These modes are very useful, for example, when the master timecode disappears during tape shuttling. Under this condition, the continuous chase‑lock mode will abort and stop the transport, whilst the free‑run mode will carry on regardless! The two last modes, however, will stop and then resync as soon as stable code appears.

The bulk of the rear panel is given over to four removable blanking plates, permitting a variety of analogue and digital interfaces to be installed. These mini‑YGDAI cards (as used in the O1V digital mixer) are fitted easily into side rails and retained by thumbscrews. See the Optional Interfaces box for more information.

In Use

I found the D24 to be a fast, reliable and largely intuitive machine. Recording quality was superb in all settings, but particularly with higher bit resolutions. The curtailed recording time at the elevated sample rates makes the machine rather impractical for many applications, although the addition of external SCSI drives helps in this regard, even if the number of tracks remains restricted to just four.

Performing the usual kind of music recording functions — synchronising to a sequencer, recording basic tracks, overdubbing and so forth — was all exactly as expected with no operational problems apparent at all, save the S/PDIF input trap! There were no sync problems during overdubs or when listening to the recorded material, and the auto‑punch system worked smoothly and flawlessly. The off‑line DSP time‑compression and pitch‑shifting processes are both very effective, with minimal glitching even at extreme settings — a useful facility in audio‑for‑video applications.

In video post‑production environments the provision of video sync, 9‑pin control interfacing and pukka timecode facilities make it easy to install the D24 but, once again, the limited recording capacity is a problem when dubbing typical half‑hour programmes. However, the comprehensive chase sync modes and remote control options permit superb integration, and a machine fitted with an external hard drive would function well in this environment. It is, therefore, a great shame that Yamaha have chosen not to support any kind of file interchange with the established formats (SDII, BWAV or AES31, for example). The industry has been fighting for years to achieve reliable interchange of disks between systems (hence the latest AES standard) which virtually every other manufacturer now supports in one form or another. You might be able to handle a Pro Tools disk on an Akai, for example, but a Yamaha disk will be no use to anyone else... yet!

All in all, the D24 is impressive. It is one of those machines which does exactly what it says on the box. However, potential users will need to think carefully about the best configuration for their particular application in terms of YGDAI cards and external drives, both of which will add to the basic machine's list price. The inherent limitation of the 640Mb MO disk is a double‑edged sword; it will appeal to those who don't need long recordings and don't want to worry about backing up or restoring. However, anyone wanting greater recording times may overlook the potential of the machine if they stop reading at the 640Mb line! I highly recommend closer inspection of the D24 if you are looking for a disk‑based modular digital multitrack.