Alesis ADAT HD24
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The Alesis HD24 is a 24-track hard-disk audio recorder. It is the successor to the hugely successful tape based Alesis ADAT. Its main advantage over the traditional ADAT is its use of IDE hard disks rather than tape, leading to faster location of specific points, better editability and easier transferability. Furthermore, hard disks are much more reliable than tapes which can be easily damaged.
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[edit] Advantages over tape-based ADAT
There are numerous advantages that the HD24 has over the tape-based ADATs. Primarily, the hard disks capability for random access allows for much better accessibility. For example, when looping on the original ADAT the tape had to rewind when it reached the end of the loop, resulting in a period of no output sound. However, the HD24 can instantly jump to any position in a song without any gap. The time saved in rewinding and fast forwarding is enormous, and returning the beginning of the song takes as long as actually pressing the button.
Another massive advantage is that the HD24 can record and play back 24 tracks of audio, not just 8. The HD24 can be considered as three ADATs in the space of one.
The built in Ethernet port allows for the easy transfer of files to a computer, which could only be done with a specific PCI card with the previous ADAT. This feature means it is now easy to transfer an imperfect track to a Digital Audio Workstation, alter it, then transfer it back to the HD24. However, transfer speed is limited to 10 Megabit per second.
The HD24 also permits 25 locate points per song, the ability to name songs and all the features of the traditional ADAT.
[edit] Advantages and disadvantages compared to computer-based recording
Although it is possible to edit audio within the HD24, computer based systems offer a lot more editing power. The additional benefits of computer based recording mean that the HD24, or any stand alone multitracker, is now not the preferred choice of many audio engineers. However stand-alone solutions are often perceived as being more reliable than computer based solutions.
[edit] File storage and transfer
Alesis developed their own method of writing to disk which interlaces the audio of the various tracks on disk. Although this does not entirely resolve fragmentation issues, it greatly reduces them. This prevents many seek operations, allowing the HD24 to use cheap IDE drives for 24 track audio storage.
Disks formatted with Alesis' proprietary FST file system are not currently recognized by today's operating systems. Therefore, to permit interoperability between computers and the Alesis ADAT HD24, Alesis offers two options. The first option is transferring the files via the built-in FTP server of the HD24. This does not require any additional hardware, but is generally considered slow, and many users have experienced dropped connections (which has been attributed to expired DHCP lease).
The second option is the Alesis Fireport, which is basically an adapter from the hard drive's IDE connection to Firewire. The Fireport is shipped with a piece of software, FST/Connect, which is capable of reading the FST file format on Windows and Macintosh. This allows for files to be transferred to and from a computer completely separately from the HD24 itself. At 400 megabit per second, Fireport transfers can in theory be done at 40 times the speed of FTP transfers. However, in reality, this rate is seldom achieved as the throughput of the hard drive itself can be a limiting factor.
File transfers have enormous potential for cutting studio costs: An artist can record at a professional studio and have the audio transferred onto his or her own hard drive. This then allows the artist to take home the audio, and edit the parts at the client's own leisure. The final result can then be transferred back to the hard drive and used for the mixdown back at the studio - cutting hours of studio time and saving a lot of money.
[edit] Compatibility
The Alesis ADAT HD24 offers good out-of-the-box compatibility, both with existing ADAT systems and PC-based solutions out of the box.
The HD24 has MIDI in and out and can transmit MTC (Midi Time Code), which allows for easy synchronization to other hardware, however it cannot synchronize to incoming MTC. The HD24 supports MMC (Midi Machine Control) in two directions. It also features three Alesis Lightpipe ins and outs (tape based had one of each), which each can transfer eight tracks of digital audio at once.
The HD24 also has 9 pin synchronization ports, dedicated to sync with other ADAT machines. An HD24 can easily be integrated into an existing tape based ADAT system, although there are a few issues with compatibility between the two; for instance, by default HD24s start each song from zero (although the zero-offset can be moved), whereas the tape based ADATs continue to the end of the tape no matter how many songs are recorded.
The software that is shipped with the Alesis Fireport is available for PC (Windows) and Mac. For Linux, a small third-party suite called HD24tools exists. Since its creation, the HD24tools suite has been ported to both Windows and Mac. This third-party software is able to read Alesis ADAT HD24 disks, but not to write them. It does however permit the use of alternative external drive solutions in addition to the Alesis Fireport.
The original Alesis HD24 drive caddies were designed by a company called ViPowER, Inc. This company also produces the ViPowER SuperRack. The ViPowER SuperRack model VP-10KFU-133 is an internal PC drive bay known to be compatible with the HD24 caddies, albeit not hot-swappable. The VP-1028LSF is a internal ADAT-compatible USB-based alternative which does offer hot-swappable operation, albeit slightly slower at USB transfer rates. ADAT Compatibility of yet another model, the VP-1528LSF, is expected but has not yet been confirmed.
The HD24tools suite also operates very well with hard drives connected via external hi-speed USB enclosure, so it is not necessary to use a desktop PC, and using USB provides a hot swappable solution (but always remember to power off the enclosure itself before swapping the drives).
It should be noted that Alesis' FST/Connect fireport software only supports drives that are connected via FireWire and will therefore not work with aforementioned drive bays.
[edit] Known issues
FTP transfers are known to be slower than real-time and not very reliable; this has been attributed to lost DHCP lease. Both of these issues can be overcome by obtaining the Fireport.
Power outages during recording may result in lost recordings, leaving the drive in a corrupt state. This is due to the allocation information of a song only being written to disk when STOP is pressed. The power loss problem can be addressed by powering the HD24 recorder via a UPS. Alternatively, one can pre-record silence with the expected length of the recording or longer. Often, it is possible to recover the audio that was lost due to power outages.
Hard drives that are kept on a shelf unused for a long period of time may stop functioning and no longer spin up. This is due to the lubricant of the drives setting, and not a problem inherent to the Alesis ADAT HD24 recorder itself. The problem can be overcome by regularly spinning up the drives and by making regular backups.
Some users have reported the HD24 recorder to fall out of record mode when used in extremely noisy environments due to sonic vibrations. This has reportedly been overcome in several ways, among others fixing the hard drive to the chassis of the recorder; placing the recorder on a soft surface (such as a blanket); or simply shielding the recorder from the loud sound.
One method that has worked successfully is to loosen the two retaining screws for the D type connector at the back of the disk caddy. There is a possible design flaw in the HD24 where the connector is firmly attached by the two screws leaving no tolerance, which means that the caddy remains in tension and can pop out spontaneously or as a result of vibration. Singer Songwriter Dino Dini had this problem and successfully remedied it by slightly loosening the two screws, allowing a little bit of give so that the caddy inserts better and the drives no longer pop out. See picture.
[edit] Support
The HD24 forum on yahoo groups is the prime source of support for the Alesis ADAT HD24 recorder. This group is also monitored by Alesis.
