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Alesis HD24

Multitrack Recorder By Paul White
Published February 2002

The new tapeless ADAT provides 24 tracks of hard disk recording at less than the price of the original eight‑track.

Alesis HD24Many years ago, I tried to convince Alesis that it might be a popular move to build a tapeless ADAT, but at the time hard drives were still expensive, so all I was envisaging was a simple eight‑track system. I argued that, by incorporating the nine‑pin sync and optical connectors of the original tape machine, ADAT tape and ADAT hard drive could be mixed within the same system, enabling Songs to be archived to ADAT tape via the optical digital link when finished. At the time, Alesis chose not to go that route, but last year the company announced the HD24, which meets my wish list and more. Since that announcement, Alesis has been bought by DJ company Numark, but, happily, Numark saw fit to include the HD24 in their marketing strategy.

First Impressions

In some ways the Alesis HD24 looks rather basic compared to some of today's hard disk recorders, but it offers up to 24 tracks of 24‑bit recording at 44.1kHz or 48kHz (or 12 tracks at 88.2kHz or 96kHz with the addition of a forthcoming optional converter card). Unlike some systems, where I/O cards add to the basic cost, the machine comes with balanced jack analogue audio I/O for all 24 tracks, plus three pairs of ADAT‑format optical I/O. The HD24 also features the nine‑pin sync and remote control compatibility of its tape‑based predecessor, which is extremely good news for existing ADAT owners, as it makes it very easy to transfer projects from tape to disk and vice versa, even though tape‑based ADATs are limited to 16‑ or 20‑bit recording depending on the model. Up to five HD24s can be sync'ed to give 120‑track capability with single‑sample accuracy, and the machines may be controlled directly from their front panels, from the included LRC (Little Remote Control) or from a regular Alesis BRC (Big Remote Control). Basic transport operation is also available via MIDI Machine Control.

The unit ships with a somewhat modest 10Gb hard drive fitted in a removable caddy (around 45 minutes of recording over 24 tracks at 48kHz sample rate) and there's a second slot that will accept a second caddy‑mounted drive of your choosing. Recording can be to either drive, but not to both at the same time, though you can back up from one drive to another, either on a per‑Song basis or the whole drive.

Alesis HD24 removable drive caddy.The HD24 utilises a proprietary formatting system to optimise disk access speed from low‑cost IDE drives, so a drive speed of 5400rpm is adequate — most large‑capacity hard drives are now faster than this. However, a downside of this is that track‑minutes are wasted if tracks are not recorded on, just like tape. At one time this would have been a tragic waste of valuable storage space, but given that you can now buy IDE drives up to 100Gb in capacity for less than the VAT I paid on my original 600Mb drive, this isn't such a big deal. Based on track minutes, hard disk is now as cost‑effective as ADAT tape. What's more, you can set the number of tracks on a per‑Song basis to two, four, eight, 12, 16 or 24 to minimise wastage, so if you select 12‑track mode and record 10 tracks, you only waste the disk space for two tracks, not for 14. This formatting system, known as FST, keeps the audio tracks from a Song in adjacent sectors, which provides a very fast seek time and allegedly reduces fragmentation quite significantly. Certainly I experienced no problems when performing multiple drop‑ins across all 24 tracks, even when doing several in rapid succession.

Editing is limited to basic cut/copy/paste operations, across multiple tracks if necessary, and, to facilitate this, 72 track minutes of drive space (calculated at 48kHz) are 'ring‑fenced' for use in editing. Edits can be undone up to 99 steps, space permitting, but recording operations can't be undone, which could be a bit nerve‑racking when you're doing tight punch‑ins. On the other hand, it does mean you can do multiple drop‑ins without stopping the transport, which I find essential for patching up vocal takes and so forth.

When the undo drive space is full, or if the number of edits exceeds 99, old operations are automatically discarded and replaced by the most recent. The capacity of the reserved drive space allows for one copy operation of up to 90 seconds long across all 24 tracks, though you can disable the paste undo facility to double this capacity when copying long sections of multitrack audio.

Nuts & Bolts

Physically, the Alesis HD24 occupies the same rack space (3U) as the previous ADAT machines, and the front panel is set out in a similar way, making it very easy to operate. Above the two drive bays are 24 bar‑graph meters with user‑selectable peak hold options, and beneath each is a rather small track selection button. The drives must be unmounted using their respective Drive buttons before they can be removed from the machine, and an LED beneath the currently active drive flashes alternately red and green. Basic software drive repair tools are included within the system, so minor damage caused by unplugging a mounted drive can usually be fixed.

The right‑hand side of the panel is given over to the plasma time display, the edit/locate controls, the transport keys and a number of other buttons dedicated to setting the metering and monitoring modes, the input source, clock source and so on. Though somewhat small, none of these buttons are multi‑function, other than the cursor up and down buttons, which double as Yes/No buttons. Like the ADAT, a red segment comes on at the bottom of the track meter when a track is armed for recording and, to simplify editing, a blue box appears around the bar‑graph meter of any track selected for editing.

Around the back are 24 balanced jacks for the analogue ins and outs, and there's a user‑configurable normalising system for the inputs, so that if you only ever use, say, eight inputs, these can be left connected and will feed all 24 tracks in banks of eight. This system can accommodate mixers with two, four, eight, 12 or 14 outputs. Each of the ADAT optical connector pairs can handle eight tracks at regular sample rates or four tracks at the higher sample rates, so the three pairs always provide full access to all available tracks. Similarly, the ADAT nine‑pin sync has both inputs and outputs to enable the Alesis HD24 to be used as part of a multi‑machine system. When connected to a BRC, the input sync source is automatically selected so that the BRC is master. Where one or more machines in a system is an ADAT tape machine, the tape machine should be made the master due to its considerably longer locate and lock times.

Another piece of ADAT legacy is the varispeed control, which offers ±200 cents of pitch change at a sample rate of 44.1kHz or +100/‑300 cents at 48kHz. As this works by varying the sample rate, it can only be used when the machine is running on internal sync, not when it's sync'ed to other devices that have a fixed clock rate.

Alesis HD24 rear panel connections.An Ethernet connector enables the HD24 to function as an FTP server to allow audio files to be transferred to or from a computer (see 'Ethernet Facilities' box) and, unlike the original ADAT, there's also MIDI In and Out, making it possible for the machine to follow or generate MMC commands, and to output MTC. A word clock input BNC connector is also fitted, along with a jack that accommodates any momentary‑action footswitch for remote drop‑ins. A second jack hooks up to the included LRC, which is the same as that supplied with the tape‑based ADATs, providing basic transport control and a limited number of locate points.

A hard power switch is mounted next to the IEC mains input. When powered on, the machine can be switched into standby mode from the front panel. This switch parks the drive heads, so should always be used before shutting down via the rear‑panel mains switch. A large grille gives away the presence of an internal cooling fan.

Onboard Ethernet Facilities

The HD24 uses Ethernet to allow it to share audio files with a computer or network of computers. Once a connection has been established, tracks may be exported as either AIFF or WAV files. Similarly, audio can be transferred from the computer to the HD24. There's even a password system that allows you to hook up the HD24 to the Internet so that anyone with a password can access its audio files, though I have to admit that this isn't something at the top of my priority list. When Ethernet is active, the machine can't be used to record or play as it essentially functions as an FTP server, and audio transfer can be slow. For example, even with a following wind, a four‑minute, 24‑track Song will take at least 16 minutes to transfer.

Before the HD24 can be connected to a computer, you need to set the IP address and subnet mask and put it into server mode, a task that can be accomplished via the Utility button and menus. If you're on a network, then the IP address needs to be set up accordingly, but if you're working with a single computer, the manual provides default address and subnet mask values that will work in most cases. Files may be transferred via a common web browser such as Microsoft's Internet Explorer or Netscape's Navigator, though dedicated FTP software is advised for optimum speed. Suitable packages for both Mac and PC are recommended in the manual. Using a browser, it is necessary first to type in 'ftp://' followed by the IP address set up for the HD24, after which the audio can be downloaded into a folder as AIFF or WAV files. From there, the files can be imported into a suitable audio software package. To be honest, unless you're into networking, this all looks a tad heavy going, and piping audio into the computer via a soundcard with an ADAT port will almost certainly be simpler and faster. I'd also have appreciated a digital camera‑style drag‑and‑drop mode where the HD24 mounts as an additional hard drive, enabling Songs to be dragged across as folders, but sadly, it isn't that simple.

Firing It Up

Each new recording to the Alesis HD24 requires the user to create a new Song. Each Song can be set up with its own sample rate, track count and name. Up to 64 Songs can be created per disk, though there's no rule that says you only have to record one musical song into each of them. In HD24‑speak, a Song is simply a chunk of recording time along with its track count and sample rate parameters. Time starts from zero (unless you enter an alternative value) for each Song and the Song end is defined once the first recording pass has been made, so it's important to allow for any overdubs that may overhang the end of the Song by recording extra time on the first pass. There's no way to pre‑roll before the beginning of a Song and Songs can't be extended once started, though a possible workaround is to set up a new, longer Song and then copy/paste the Song you want to extend into it, copy buffer size permitting. Note that if you're planning to sync to a tape ADAT, for backing up or combined tape/disk recording, it's advisable to leave at least ten seconds of blank space at the start of each Song to give the tape enough time to lock properly.

The smaller LRC remote is supplied as standard with the HD24.The smaller LRC remote is supplied as standard with the HD24.When connected to a BRC, the HD24 behaves like three of the earlier ADATs. Most of the BRC functions work normally, though the HD24 can provide both negative and positive track delays (±170mS) which the tape version obviously couldn't, so negative delays have to be dialled in from the HD24 front panel. Furthermore, the BRC can't be used to set up pre‑ or post‑roll times that fall outside the Song boundaries. It's also important to note that the BRC is designed to provide a 48kHz clock rate — it can just about manage 44.1kHz if you use the pitch control function, but it can't be used if you're working at the higher 88.2 or 96kHz sample rates.

While tape fast winds in a well‑known and predictable way, hard drives can locate in an instant, so the transport controls function slightly differently to those of a tape recorder. Stop, Play and Record work normally, though it must be noted that you can only enter record by pressing Play and Record together, at which time any armed tracks will go into record mode. You can't work the other way around, by putting the machine into record first and then using the track arming buttons to punch in.

Rewind can be pressed momentarily to make the playback jump back by five seconds, or it can be held down to achieve an accelerating rewind in much the same way as tape. Forward wind works in the same way, though it's also possible to use both forward and rewind in conjunction with Stop to achieve low‑speed audio scrubbing.

Monitoring works in the same way as on a tape ADAT, with dedicated buttons for All Input or Auto monitoring. Auto mode is generally used after the initial recording has been made, so that the monitoring automatically switches from the track to the input source when punching in.

To help with navigation, each Song can make use of up to 24 time locations (if you include the Edit Start/End and drop‑in markers). Markers one and two are used by default when setting up a loop, which you may want to do when rehearsing a specific section of a Song. Locate points one to 20 are general purpose and may be stored on the fly or when the transport is stopped, just as with a tape ADAT. Locate times are referenced to the Song start time and move relative to it, so that they stay at the right location within the Song. If you've used a BRC before, you'll find the system very similar indeed, right down to the ability to directly edit locate times. The Locate button takes the transport to the currently selected locate time.

Various automatic functions can be achieved using the locators in conjunction with the Auto Return, Auto Play and Auto Record buttons. When Auto Return is active, playback jumps to the loop start marker as soon as the loop end marker is reached, while in Auto Play playback begins from the locate position as soon as the Locate button is pressed. Auto Record handles automatic drop‑ins based on locate points 21 and 22 (with a rehearse option) while points 23 and 24 function as the Edit Start and End markers. It's also possible to combine automatic recording with looping if you need to keep going over a specific section, though my own preference is to punch in manually using the transport controls, or to use a footswitch if I'm playing guitar at the same time.

The Specs

Though figures don't tell you everything about how a piece of equipment sounds, the spec of the HD24 is impressive. Recording uncompressed PCM audio, the HD24 has a frequency response of 20Hz to 22kHz ±0.5dB with a signal‑to‑noise ratio better than 103dBA. Distortion is a minuscule 0.003 percent, while the dynamic range is claimed as being 144dB digital in to digital out, and better than 103dB via the analogue I/O. The A‑D converters use 128x oversampling as standard, and if the 96kHz optional board is fitted (a dealer installation), it replaces the existing board. Like the ADAT tape machine, the analogue I/O is calibrated so that +4dBu is ‑15dBFS.

Editing Facilities

With a tape machine, the only editing you can do without copying to a second machine is to punch in and out, something the HD24 does extremely smoothly using the same default 10mS crossfade as the original ADAT. However, we expect more from hard disk than mere tape emulation, and there are several buttons dedicated to editing, all of which revolve around the use of the Edit Start and Edit End locators. To set these times, it is necessary only to hold down the Locate button and then press the Edit Start and Edit End buttons at the appropriate times. These edit points may be adjusted in the same way as other markers by manually entering or changing time values.

By using the Track Edit button in conjunction with the track record enable buttons, it is possible to select one or more tracks as editing sources or paste destinations. There's a useful audition mode that allows you to hear only the selected tracks playing back from the Edit Start point, though a more useful option would have been some means of auditioning how the paste transition would sound before actually doing it.

The basic edit moves comprise Cut, Copy and Paste (either within a Song or from one Song to another) where a paste operation will overwrite whatever audio data was previously in that location. Note that Paste Undo must be enabled in order to undo paste operations, even though cut and copy moves can always be undone. While these basic edit operations are adequate for many uses, and clearly are more flexible than working with tape, it would still have been useful to have an edit mode capable of removing a section of audio while joining up the two cut ends (for taking out excess bars for example) and for inserting sections.


I've been using ADATs, often in multiples, since the format was invented, but I've never learned to live with the slow response of what is essentially a VHS video transport. Even one machine takes a few seconds to go into play mode from stop, and trying to lock up multiple machines is like waiting for the launderette spin cycle to finish. On top of that, the odd tape gets chewed after you've spent hours working on it, and usually minutes before you were planning to make a backup!

Coming from this background, the HD24 is an absolute joy to use because you can treat it very much like a tape ADAT, but without having to suffer the indignities of endless lockup times or slow rewinding. Moving through Songs is fast and easy, even without using the locators, and being able to start playback instantly or return to the start of a Song in an instant is extremely refreshing. Unfortunately, the fan noise is roughly equivalent to the whirring of a regular ADAT transport, but you can at least use the LRC or a footswitch to record sensitive parts from the other end of the room. It's sad that recordings can't be undone, which I guess is down to the limited size of the undo buffer, but again you're no worse off than you were with tape. If you fudge a punch in, you can always record the section again, just like in the old days — it's invariably faster than using technology to salvage something!

As I commented earlier, the edit functions are very basic, especially in the light of what you can do in a computer, but, being realistic, you're most likely to need the ability to copy good vocal choruses or bits of guitar solo, and this you can do (and undo) quite easily. However, if you decide to extend a Song by copying verses, you may find that you haven't left enough space at the end of the Song, and if you're using all 24 tracks, the longest section you can copy over to a new Song in one go is 3 minutes with the paste undo buffer switched off. There are also some edit moves that are noticeably absent, and I found some of the front‑panel buttons, including those used for editing, to be rather small and quite difficult to read.


The strength of the HD24 is not its sophistication, but rather its transparency and smoothness of operation. It can function in an ADAT environment, it can make use of your existing BRC, though a good external word clock is needed to tame the BRC's notorious jitter, and (not to be overlooked) it provides full balanced analogue plus ADAT digital I/O as standard. Though the editing facilities are limited, they're better than you get from tape, while having dual drive bays provides a practical and cost‑effective means of backing up projects.

I feel the Ethernet solution to archiving is rather slow and cumbersome, but at least it's available. For existing ADAT owners, being able to move material between platforms is a real bonus. At least you can use your existing ADATs to archive HD24 recordings (albeit by compromising the bit depth) to single‑sample accuracy, making it possible to back up all 24 tracks onto three ADAT tapes in three passes using just a single ADAT tape machine. During the course of this review I transferred an entire tape‑based project to the HD24 for mixing, and, though my working method stayed essentially the same as with tape, I found it much faster and far less stressful — I wasn't always worrying that the tape might get chewed!

Sound quality is hard to define at this level, as modern converters tend to behave so well, but, subjectively, the HD24 is similar to the 20‑bit ADAT XT, though those extra four bits give it additional low‑level resolution, at least in theory. It also has a workable built‑in backup strategy and it's easy to sync multiple machines if you really need more tracks. The high sample‑rate options are available for anyone who feels they need them, but, for my money, I'd rather have the extra tracks! A high sample‑rate board wasn't provided with the review model, but I'd have thought that any sonic differences would be likely to be negligible when working in a project studio environment.

Naturally there are some things I don't like, other than the audible cooling fan and the small buttons, such as the machine's inability to play all the Songs on a drive automatically in sequence, which would have made unattended backup to ADAT tape possible. As it is, you have to recall and start playback afresh for every new Song. I also feel the edit features could have been made a little more flexible, perhaps to include insert and 'cut and join up' modes or, more importantly, a better way of auditioning paste edits before you commit to them, which is especially important if paste undo is disabled.

Ultimately, if you look upon the HD24 as a 24‑track, tapeless ADAT with a few editing features thrown in for good measure, you won't be disappointed. It works smoothly, you can tackle the learning curve in slippers, not crampons, and it eliminates the worst frustrations of its tape‑based predecessors, one of which ate a brand new tape during the course of this review! It may not have all the bells and whistles of the competition, but if you like everything about the tape environment other than the tape itself, the HD24 is a straightforward and affordable alternative.

HD24 MIDI Functionality

The HD24 responds to MIDI Machine Control messages and can also generate them. There's no SMPTE generation facility, but MIDI Time Code (MTC) is available, albeit at a fixed 30fps. The MTC start point is the same as the Song start point, so offsets can be introduced by changing the Song start time value. Additionally, the MIDI In port can be used to load in software updates, and all MIDI‑related facilities are accessed via the MIDI button and the cursor keys.


  • Up to 24 tracks of simultaneous recording.
  • 24 tracks of analogue and ADAT digital I/O provided.
  • ADAT‑compatible sync and remote control facilities.


  • Recording time not dynamically allocated.
  • Small buttons.
  • Limited editing functions.
  • Unlike edit functions, recording actions cannot be undone.
  • Audible fan.


For less money in the UK than the original ADAT, you get 24‑track recording capability, ADAT sync and optical I/O compatibility, and a very straightforward user interface. Will probably appeal most to existing ADAT users.


HD24 £1999 including VAT; optional converter board for higher sample‑rates, £tba.

Numark +44 (0)1252 341400.

test spec

  • Alesis HD24 OS v1.00