Alesis AI-1

Digital Interface/Sample Rate Converter

As an ADAT user, one of the things I appreciate most is the ability to mix directly onto two tracks of one of my ADATs. Though this doesn't, at first, seem to offer any advantages over mastering directly to DAT, the perfectly seamless punch‑in and punch‑out of ADAT means that if you mess up part of a mix, you can simply go back and drop in — unlike DAT, where you have to run the whole mix again. If you think about it, this offers nearly all the advantages of mix automation without any of the hassle or extra expense.

Unfortunately, because ADAT records at 48kHz, and because ADAT's optical interface carries all eight tracks at once, you can't simply plug in a DAT machine and clone your master mix — you have to go via the analogue domain. At least, that was the case until the AI‑1 came along.

The Alesis AI‑1 is a straightforward 1U box, at the heart of which is a two‑channel sample rate converter. You can feed a 48kHz stereo digital signal in at one end and a 44.1kHz version comes out of the other — or vice versa. Aside from sample rate conversion, the AI‑1 is also able to convert between S/PDIF, AES/EBU and ADAT formats. When working with ADAT, the AI‑1 is able to send or receive pairs of ADAT tracks as stereo signals, and the selection of track pairs is made using the AI‑1's front panel. The AI‑1 is also compatible with the Alesis BRC, and in multiple ADAT systems, the BRC may be used to provide remote control of the AI‑1's functions.

Alesis have striven to make the AI‑1 as intuitive to use as possible; the front panel hosts buttons for selecting the signal source, the signal destination and, if an ADAT is involved, which pair of tracks is concerned. The AI‑1 automatically recognises the source signal's sample rate, and a pair of buttons allow the user to select a destination sample rate of either 48kHz or 44.1kHz. All the buttons include status lamps but, other than the power switch, there's nothing else on the front panel.

The rear panel is, if anything, busier than the front, with in and out connectors in all three digital formats: optical for ADAT; optical and phono for S/PDIF; and XLR for AES/EBU. There's also a BNC connector, which provides a 48kHz clock output, and a pair of ADAT 9‑pin sync sockets for use when the AI‑1 is hooked into a multiple ADAT/BRC system. In a BRC‑driven system, the 48kHz clock feeds into the BRC and the AI‑1 is also linked into the ADAT chain using the 9‑pin sync connectors. Power comes in via a mains IEC socket, which makes a nice change from the dreaded wall‑wart!

Applications

The fact that the AI‑1 is designed as a companion for ADAT doesn't preclude its use as a sample rate converter between two DAT machines; most home users work with domestic DAT recorders which offer a fixed sample rate of 48kHz, but using the AI‑1, tapes can be cloned onto a second machine at 44.1kHz. When working with the BRC, the AI‑1 is largely controlled from the BRC, and when transferring data from an external source to ADAT, the destination track pair is set up using the BRC Record Enable buttons.

As intimated right at the start of the article, ADAT users who like to mix onto a pair of ADAT tracks rather than direct to DAT now have a way to digitally clone their work. Similarly, any part‑finished work which exists on DAT may now be loaded onto two ADAT tracks for overdubs to be added on the remaining tracks. This alone is food for thought when it comes to writing material 'by post'. Now, instead of sending a cloned ADAT tape to your songwriting partner, you can simply send a finished DAT mix of the song so far, over which the appropriate vocals, solos or whatever can be overdubbed once the DAT contents are transferred to ADAT, again using an AI‑1.

Summary

The AI‑1 is a very straightforward unit that performs the complex task of sample rate conversion with almost casual ease. I could detect no difference in sound quality between the input signal and the sample‑rate‑converted output, nor did I expect to. The only problem might arise when transferring material from a DAT machine that records with pre‑emphasis; although the AI‑1 passes on the de‑emphasis flag, it doesn't actually de‑emphasise the data. The outcome of this is that transferring tapes made on a Casio or Tascam portable DAT machine to ADAT will result in the ADAT playing back the material un‑de‑emphasised, so although the recording will play OK, there'll be far too much top end.

Most of the applications of the AI‑1 are pretty obvious, but the slightly less commonplace uses might include transfer to and from hard‑disk recorders, use of ADAT to back up stereo DAT masters, and transfer of CD sound effects material to ADAT. Ultimately, not every ADAT owner will feel a burning need to own an AI‑1, but I can think of several situations where I'd have been very glad to have one around, including the times when I've wanted to sample rate convert a DAT master at the same time as loading it into Sound Tools for editing. With the AI‑1, all these things are possible. Given the quality of sample rate conversion and its ability to interface between different digital standards, I feel the AI‑1 is something of a bargain, when you consider that only a year ago you could have paid around £2,500 for a professional unit doing substantially the same job.