Alesis ADAT HD24 IDE Hard Drive Recorder

The Alesis ADAT was undoubtedly one of the most influential and successful recording products of all time. Today, though, hard drives and computer processing

The Alesis ADAT was undoubtedly one of the most influential and successful recording products of all time. Today, though, hard drives and computer processing are so inexpensive that digital tape makes less sense as a recording medium. Not only do hard disks permit instant random access and much easier editing and backup, but they also require less maintenance and have no mechanical tape mechanisms to get stressed.

Tape-based ADATs are still in Alesis's product line — a good thing, considering the millions of ADAT tapes that have been recorded. But digital multitrack tape's days of dominance as a recording format are probably over, and the folks at Alesis know it. With the ADAT HD24, Alesis joins the movement toward hard-disk recording.

Given the appeal of the ADAT's familiar tape-recorder-style operation, it makes sense that Alesis made the ADAT HD24, ADAT's successor, a standalone recorder that records onto inexpensive IDE hard drives. This new 24-track ADAT brings its ancestors' good points to a much better recording format. The ADAT HD24 uses the ADAT's 9-pin sync interface to lock multiple machines with single-sample accuracy and to synchronize their transports. The new unit even has the same 3U rackmount form factor, enabling it to directly replace or augment tape-based ADATs (see Fig. 1).

One interesting feature carried over from the original ADATs is the ability to slip tracks backward or forward by as many as 17 ms. (This subject could make a short article of its own, but time-aligned tracks often make a surprisingly large difference to the sound in multimic drum setups.)

Like previous ADATs, the unit comes with an Alesis Little Remote Control (LRC), which includes transport control and the essential recording and location functions. You can also control the recorder remotely using MIDI Machine Control (MMC). The MIDI I/O is also used for MIDI Time Code (MTC) output and for updating the firmware.


The Alesis ADAT HD24 has 24 channels of balanced ¼-inch TRS analog I/O, which operate at +4 dBu. You also get 24 channels of ADAT Lightpipe digital I/O (see Fig. 2). That makes the unit an exceptional value by eliminating the need for additional cards.

The Alesis ADAT HD24's analog converters operate at 44.1 or 48 kHz, and Alesis has announced an optional 96 kHz I/O board. You can run the stock unit as a 12-track, 88.2 or 96 kHz recorder using the Lightpipe I/O and external A/D and D/A converters (you need both, and I was unable to test this feature). To accomplish high-rate sampling, the machine uses a sample-splitting scheme that sends alternating samples to two channels. Each channel sounds normal when played back on 44.1 or 48 kHz equipment. Unless the receiving device is capable of reuniting the split 88.2 or 96 kHz track, however, you cannot use external signal processing that will change the data. That includes crossfades, EQs, and, in some cases, gain changes.

On the other hand, you can copy and move the audio data in a digital audio workstation (DAW) and transfer it back into the Alesis ADAT HD24 via FTP, using the recorder's built-in 10Base-T Ethernet port. If you take that approach, the 88.2 or 96 kHz track is automatically reunited, so you can edit the data and transfer it back to the HD24.


The Alesis ADAT HD24's IDE hard drives are mounted in removable caddies that slide into its two bays. One caddy comes with a 20 GB drive; the other is empty. Installing hard drives into these caddies takes approximately 90 seconds; you can use any 4-inch IDE (or compatible variants, such as the Ultra ATA/100) drive with a spindle speed of 5,400 rpm or greater, and the drives are hot-swappable. The maximum drive size is an impressive 2 terabytes (TB); that's 2,000 GB! The review unit's stock 20 GB disk performed reliably during the few weeks I tested it.

At the time the Alesis ADAT HD24 was being developed, the inexpensive IDE hard drives that were available weren't always up to handling 24 tracks of 24-bit, 48 kHz audio. So Alesis came up with a patent-pending Alesis FST hard-drive format to improve disk performance.

FST writes data sequentially rather than at random points across the drives, cutting seek time dramatically and eliminating the need for disk defragmentation. Alesis claims that this eradicates problems that have allegedly plagued other manufacturers' recorders and reduces wear and tear on the drives. A nice plus is that the system works with any currently available drive. On the other hand, this proprietary format can't be read by standard computers.

However, one could reasonably debate the degree to which the performance of other 24-track hard-disk recorders is impeded by their hard-disk formatting, and 7,200 rpm Ultra ATA/100 drives that outperform standard IDE drives are inexpensive. Furthermore, with certain notable exceptions, most hard drives have remained in service for years when formatted the old-fashioned way. Using standard PC formatting also allows you to swap drives between desktop computers and DAWs, something you can't do with an HD24. Given all that, it's reasonable to question FST's significance.

At the least, the proprietary format indicates that a serious development effort went into this recorder; it isn't just a computer and sound card in a box with some buttons and the Alesis ADAT name. Certainly, most studio owners will be delighted with not having to defragment their hard drives.


In giving the Alesis HD24 a once-over and going through its menus, I learned that it is easy to use. In addition, the manual is clear and complete. Anyone familiar with recording gear could walk in and use this machine.

Of course, you still have to read the manual to learn a few things — for instance, that the machine can store 64 songs on a drive, and that you hold Stop and Rewind/Fast-Forward on the machine (not on the LRC) to scrub audio for editing. But even deeper functions such as the MIDI and sync features and disk housekeeping are obvious.

Buttons are grouped logically by function; they may be related to file or name, editing, location, digital sync, or digital I/O. You navigate through a selection using a set of four arrows. The display guides you clearly, even when you've done something that makes no sense, such as trying to make the machine play before it has loaded a song.

Except for the lighted transport buttons, all of the ADAT HD24 buttons are made of the type of rubbery plastic found on other Alesis products over the years. In my experience, they stand up well to repeated stress.

You set levels using dedicated ten-stage peak-reading meters for each channel (the meters are calibrated at -15 dBFS). Like most recorders made today, the Alesis HD24 has no input controls, so gain must be adjusted at the source.

The unit provides 20 autolocation markers and offers dedicated buttons for seven of them. Some markers are dedicated to the in/out points for loops, punches, and edit points. One surprise is that the name in the display doesn't necessarily reflect the current location. Instead, it's set up so you can scroll to the location you want to go to before hitting the Locate button.

The Alesis ADAT HD24 doesn't provide virtual tracks — the popular “take” or “playlist” feature that lets you record and store several alternate takes for each of the 24 physical tracks. The standard auto punch-in/out and rehearsal features are included, and you can control them with a footswitch for hands-free operation.


The Alesis ADAT HD24's answer to people requesting more features is to make it simple to transfer audio into a DAW. One way of doing that is by using its built-in 10Base-T Ethernet port, which allows you to set the unit up as an FTP server on your network and transfer files to another computer for editing or processing. If you have a fast Internet connection with a static IP address, it would even be practical to share files on the Web.

Setting up the machine for networking is easy, though in practice it's probably easier and usually faster just to transfer the files in real time over the Lightpipe interface. That's especially true when you're moving lots of tracks back and forth, because 10Base-T isn't all that fast, and the ADAT HD24 sends tracks that extend the length of the song, not just selected regions. I'd love to see 100Base-T or even gigabit Ethernet in a future version of the machine.


The sync features all work reliably on the Alesis ADAT HD24. Like every ADAT, the HD24 supports Alesis's standard ADAT 9-pin sync. In addition, thanks to its MIDI Out port, the ADAT HD24 can send MTC directly to another MIDI device, such as a computer MIDI interface. It also can receive MMC — but not MTC — through its MIDI In.

Therefore, if you only want to sync your sequencer and HD24, you can do so without an external synchronizer, although the synchronization won't be sample accurate. In contrast, most tape-based ADATs require an external synchronizer to accomplish that feat. (The exceptions are the Alesis M20, the Fostex RD-8, and the Otari V-Eight, all of which have been discontinued.)

Integrating the ADAT HD24 with MMC-compatible sequencing software is satisfying, and it isn't difficult to get it working with Emagic Logic Audio and Mark of the Unicorn (MOTU) Digital Performer. The HD24 simply appears as three ADATs in the Digital Performer Machine Control window, for example, letting you record-enable all 24 tracks.

In this setup, the MIDI sequencer uses MMC to tell the ADAT HD24 to find a given location and then play back; after that the sequencer locks to incoming MTC from the ADAT HD24. The effect is much like having the digital-audio tracks in the computer alongside the MIDI tracks: go somewhere in the sequencer, and the ADAT HD24 is right there with you. That also works with tape-based ADATs, but it's much slower.

Depending on your setup, however, you might need an external synchronizer. Fortunately, any standard synchronizer that can provide ADAT 9-pin sync can be used with the HD24, including the original Alesis BRC. I tested the unit with a MOTU MIDI Timepiece AV and a MOTU Digital Timepiece synchronizer.

Except during some of the converter listening tests, I tried out the HD24 while it was connected by Lightpipe to a Panasonic DA7 digital mixer. It's usually better to clock multiple digital-audio devices from a common source, and in my case, the DA7 mixer is the clock master; its word clock drove a MOTU Digital Timepiece, which in turn sent word clock to the HD24.


For those who do more than the most basic editing, the HD24's destructive cut, copy, and paste editing features are probably best viewed as handy extras. Using them is certainly easier than assembly editing using offset tape machines, but you need to transfer the audio to a computer for serious editing.

Using the onboard editing features is simple. Select the tracks to be edited and then define the in and out points with the aid of the HD24's scrubbing function. An Edit Preview function with a fixed 5-second preroll is useful for fine-tuning the edit points. Then, you can cut or copy the audio between the edit points to the machine's clipboard, answering, “Yes, I'm sure,” a few times along the way. Next, define the new in point and paste the data from the clipboard to replace the previous track contents. If you don't like what you've wrought, 99 levels of undo are available from backups that are automatically written to disk.

A 10 ms crossfade is applied automatically to both ends of the edit region. That's a good one-size-fits-all setting to hide edits, but it would be useful to be able to adjust the length or even disable the crossfade feature. You don't always want to crossfade into a big crash, for example, because it can smooth out the attack.

Alesis plans to release a new Medium Remote Control (MRC) that will include a jog wheel. That will be useful; scrubbing on the ADAT HD24 is difficult to control.


In a setup with a digital mixer doing the A/D/A conversion, the Alesis ADAT HD24 obviously has no sound of its own. But it has onboard converters. Judging their quality called for recording several instruments directly through a high-end signal path (using Millennia Media STT-1 channel strips) and recording several CDs. I compared the ADAT HD24's converters to several other converters in various price ranges, using the HD24's internal clock and an external clock (which didn't make any difference worth mentioning). Frankly, it's confounding that Alesis is able to include 24 pairs of converters of this quality. Subjectively — highly so — what you get back is pretty much what you put in.

Do they sound as good as converters that cost several times the price? Of course not; at least, not in all cases. Each A/D and D/A conversion is likely to cause some audible loss, especially with highly dynamic material. But the HD24's converters stand up surprisingly well. There's no reason to be afraid to use them.


Yes, the HD24 rocks. Alesis has done an excellent job of carrying forward what made tape-based ADATs so appealing — simplicity, clean sound, and value — into a workhorse hard-disk recorder. The ADAT HD24 is a viable, solid, ready-for-prime-time performer that integrates well into any studio setup right out of the box.

Nick Batzdorfwrites articles, composes and plays music, and works as a general project-studio and audio rat.

ADAT HD24 Specifications

Physical Tracks24 (at 44.1/48 kHz)Virtual Tracks0Simultaneous Record Tracks24Editing Featurescut, copy, paste, move, insertAnalog I/O(24) balanced ¼" TRSDigital I/O(3) 8-channel ADAT Optical (24 ch. total)A/D/A Converters24-bit, 128x oversamplingRecording Resolution24-bitSampling Rate44.1, 48 kHz (stock); 88.2, 96 kHz (with optional I/O)Additional Connections(1) MIDI In; (1) MIDI Out; (1) BNC 75• word-clock input; (1 pr.) DB9 ADAT sync I/O; (1) 10Base-T Ethernet; (1) unbalanced ¼" footswitch (punch in/out); (1) unbalanced ¼" for LRC remoteInternal Storage(2) hot-swappable drive bays, configured as (1) 20 GB IDE drive and (1) empty bay; maximum addressable drive size 2 TBEffects Processors0Frequency Response22 Hz-22 kHz (±0.5 dB), analog in to outSignal-to-Noise Ratio103 dBA, analog in to outTotal Harmonic Distortion + Noise<0.003%, analog in to outNominal/Max. Operating Level+4 dBu/19 dBuDisplays(1) 24 ch. × 10-segment LED peak-level meter; (1) multipurpose LED status displayDimensions3U × 13.5" (D)Weight21 lb.


modular hard-disk recorder


PROS: Solid construction. Easy to operate. Networkable. Built-in analog and digital I/O. Good sync features. Better than original ADATs. Excellent value.

CONS: Editing functions are basic. No virtual tracks. FST drive format incompatible with PCs. Ethernet port is relatively slow 10Base-T. No effects option.


Alesis Distribution LLC
tel. (800) 5-ALESIS or (201) 225-3222