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Digital Intercourse

Alesis AI-1

Article from The Mix, October 1994

Digital interface


The thing about standards is there's just so many of them (as the old saying goes), but if your digital equipment isn't as talkative as you'd like it to be, then Alesis may have the answer. Bob Dormon checks out the AI-1 digital interface, and discovers it might just get those binary-coded tongues wagging.


I was a little dewy-eyed when I opened up the box containing the Alesis AI-1. It's a simple 1u rack unit of customary Alesis ADAT styling; in other words, it's very black and could easily be mistaken for something rather boring.

But 'boring' is the last word I'd use to describe what turns out be one of the most useful digital devices known to man. High praise indeed... enough to have you asking, 'How's it gonna help me, man?'

Well, have you an ADAT? Don't worry if you haven't. The AI-1 talks to ADATs and more besides. Have you got a CD, DAT, DCC or MiniDisk? 'Cos it talks to them too. Interested? Not yet, huh?

How about if I told you you could record CDs digitally, directly to your DAT machine even 'though CDs are sampled at 44.1kHz and consumer DATs sample at 48kHz? Or be able to make digital back-ups at a sampling rate of your choice?

How about being able to play sounds from the digital output of a sampler or digital audio workstation direct to an ADAT without going anywhere near a desk? And there's more - but put simply, the AI-1 is an interface in the broadest sense of the word.

It translates the digital data of one format and then sends it out again in another. The AI-1 performs the task of preserving the quality of your digital audio recordings by enabling totally digital transfers between a whole range of formats, and their associated interfaces.

There is a catch though. The AI-1 doesn't come cheap. But when you discover all the things that it can do (sample rate conversion in particular), then it starts to look like very good value.

As easy as ADC: choose the source and its sample rate, choose the destination and its sample rate, and you're in business!


Overview



The AI-1's front panel is simple, but not deceptively so. The tasks you may want it to perform may be great in technical terms but for the user, the methods of achieving them couldn't be easier.

Twelve buttons on the front panel in two groups of six control the AI-1's functions. Lime-green LEDs within each button relay the current status. The first four buttons select the ADAT tracks that will either receive incoming digital audio from non-ADAT sources, or will be sent from the ADAT to other devices.

The next two determine the sample rate: 48kHz or 44.1kHz. The ADAT itself uses 48kHz, but using the BRC (Big Remote Controller), it can be effectively vari-speeded down to work at 44.1kHz. If you start mixing up your sample rates on the same ADAT tape you're in for a headache, as it will need to operate at one or other rate.

It won't be able to tell the difference from the tape itself. The result will be stuff playing about nine percent too fast (44.1kHz played back at 48kHz) or 8 percent too slow (48kHz played at 44.1 kHz). It's the BRC in conjunction with the AI-1 that provides the timing information when sampling rates are altered.



"'Boring' is the last word I'd use to describe one of the most useful digital devices known to man."


The six buttons on the right of the front panel deal with the routing of the digital audio. The top three determine the source: ADAT, AES/EBU or S/PDIF while those below are labelled identically: they are the possible destinations. From this, you've probably gathered that you don't need an ADAT at all to make use of the AI-1.

Suppose you're in the studio and you want to make a DAT back-up on your old Sony TCD D3, but the studio has a pro-DAT machine that doesn't have the same connectors? Well, so long as you've got the cables, it'll be no problem. The AI-1 will take the pro DAT's AES/EBU output, convert it to S/PDIF and send it out at 48kHz, so your 'consumer' DAT will accept it. It's all achieved simply with just two cables and three button pushes on the AI-1: source (AES/EBU), destination (S/PDIF) and sampling rate (48kHz).

It's that easy, as the AI-1 is just a rather fancy routing device that allows you to communicate with anything that's connected to it, so long as it's an ADAT or a digital audio device that complies with the AES/EBU or S/PDIF protocols. So if you want to play birdsong from a sound effects CD at the beginning of a track and record it to ADAT, you can do this digitally.

First, hook up the digital out from the CD player to the AI-1. Second, take the AI-1's (ADAT) optical out and connect it to the ADAT recorder's digital input. Put the ADAT in digital in/out mode, and select a pair of tracks to record. Then, on the front panel of the AI-1 select S/PDIF as the source, ADAT as the destination, the pair of tracks you wish to record onto, and go!

While the front panel is simplicity itself, the back panel is serious, to say the least. The IEC mains socket accepts a voltage range of 90 to 250 volts at 50 or 60Hz. Next is a 48kHz clock output on a BNC connector, that provides vital timing information for the BRC. Basically, if you've got a BRC hooked up in your ADAT system then you must connect this word clock output to it, otherwise the AI-1 won't work.

A cluster of four (EIAJ) optical connectors accommodate the ADAT and S/PDIF optical inputs and outputs. S/PDIF is well catered for, as there are also RCA (phono/coax) connectors here too. AES/EBU has the usual male/female arrangement for its digital interfacing. Finally, there's the ADAT nine pin D-type plugs for sync in and out.

The manual only gives uses for the AI-1's sync input; it's utilised as the last of an ADAT sync chain when a BRC is in operation. The AI-1's sync out will no doubt be employed in other devices, as the ADAT system's innovation continues to mushroom.

The AI-1 back-panel makes no compromises: S/PDIF (optical and RCA), AES/EBU (XLR) and ADAT (optical) are all catered for. There's also the ADAT nine-pin D-Type plugs for sync-in and out.


In Use



The AI-1 certainly got used, and last month's CD (compression) tutorial bears testimony to that. I'd used an ADAT system to record the voice-over on the tutorial, but the music examples were on DAT. Using the AI-1, compiling a complete ADAT tape was possible without having to re-record the music to ADAT via the desk. And once I'd mixed it all to DAT, I was able to back-up the DAT on two spare tracks on the ADAT tape via the AI-1.

Using the AI-1 without a BRC is just a matter of pressing the right buttons on the front panel, yet the BRC will actually remotely control the unit for you. Sample rate changes in the ADAT format can be performed, and all tracks are available for sending via the AI-1 to another ADAT. As for the other formats, you can still only select two tracks for transmission to them, but they don't have to be adjacent pairs. It's done using the track select buttons on the BRC when it is in digital I/O edit mode.

This BRC page has a few additions when an AI-1 is plumbed in. There's the 'bounce ADAT tracks' facility as usual. This allows digital track copying within the ADAT format. A new feature is 'select tracks to output to AI-1', which allows you to choose which ADAT tracks (if any) you want to transmit out of any of the outputs. Curiously enough, you can perform an ADAT bounce, and a transfer of a couple of ADAT tracks to another format simultaneously. The tracks for both operations can be completely different too. So you can back-up an ADAT tape, and pinch a load of brass riffs or whatever to a DAT tape or some other digital format at the same time.



"The AI-1 could certainly become something that producers using the ADAT system insist on having."


More new pages on the BRC select the destination format, destination sample rate and the digital input. I did notice when swapping digital inputs that it is easy to make the ADAT recorder(s) sound very sick indeed. When an external source such as S/PDIF is selected, the BRC automatically goes in to external sync. If, while you're still in digital I/O edit mode you then choose to do some ADAT to ADAT bouncing, the BRC won't have switched out of external sync mode, and the ADATs will whirr up and down trying to ascertain what speed they should be at, changing pitch continuously while the lime green LEDs on the AI-1 blink furiously. It's awful. You eventually realise what's happening and have to exit the digital I/O edit and knock the BRC out of external sync.

Conclusion



The AI-1 is not entirely unique - Digidesign produce their own ADAT interface which is ideally suited to the Session 8 hard disk recording system. The associated ProTools hardware also provides S/PDIF and AES/EBU interfaces but alas, has no optical S/PDIF connectors. Tascam, pioneers of their own 8-track digital multi-track (DA88), also have format convertors in the form of the IF-88AE (4 in/out, AES/EBU stereo pairs plus one S/PDIF I/O) and the IF-88SD which offers the old S/DIF-2 used on the Sony 1610/1630 U-matic digital audio mastering machines. Tascam also produce an interface for Sony DASH multi-tracks.

But the AI-1 does provide sample rate conversion, a feature that has previously cost silly money. At this price plus all the other features, the AI-1 has certainly been groomed for success. It could well become something that producers using an ADAT system insist on having. Being able to take solos or vocal takes home on a DAT, and reconstruct them with a computer based, hard disk recording setup, could certainly find favour - it might even help keep the use of commercial studio time concentrated around more important things... like music! Technology or no technology, that's what it's all about.

The essentials...

Price inc VAT: £999

More from: Sound Technology, (Contact Details)

Spec check

Number of digital audio channels: ADAT (8). AES/EBU, S/PDIF (2)
Sample clock input range: 48kHz nominal. User variable from 50.8kHz to 40.4kHz (+1, -3 semitones)
Rear panel connectors:
Sync Interfacing: Two 9 pin D-Sub connectors for ADAT/Remote Sync In and Sync Out. BNC connector for 48kHz Word Clock Out.
Digital Interfacing: Two EIAJ fibre optic jacks for ADAT digital I/O. Two EIAJ fibre-optic jacks plus two RCA connectors for S/PDIF digital I/O. Two XLR connectors for AES/EBU digital I/O.
Power: IEC AC mains connector. Power requirements: 90-250V AC, 50-60HZ, 50W max.


Sampling rates - what's it all about?

The sampling rate of a piece of digital audio equipment determines the audio bandwidth (frequency range) of the system. As a typical waveform has positive and negative phases within one cycle, your sampler must be able to sample at the very least, both points. If it can't, then it won't be able to accurately reproduce the audio that is being digitally encoded. For today's digital audio systems, sampling rates more than double the highest frequencies that the human ear can detect, which is somewhere between 16-20kHz. The reason why sampling rates are available at 48kHz and 44.1kHz is because early digital recorders were based around video transports and these were mathematically convenient figures. Why there are still two rates these days is because 48kHz is considered the 'professional' standard, while 44.1kHz (which is used on CDs) is regarded as the 'consumer' sampling rate standard. Furthermore, as it was feared by paranoid record companies that everyone would buy a DAT recorder and start digitally copying CDs, DAT had a very shaky start, even though it was never intended to be a mainstream consumer product. Nevertheless, models were produced that would only record at 48kHz, whether or not analog or digital inputs were used. And so it came to pass... that only the really expensive professional DAT recorders have a 44.1kHz sampling rate and 48kHz! Now, all the consumer DAT models sample analog audio at 48kHz and won't allow digital transfers at 44.1kHz even with the SCMS (copycode) implemented. Fortunately, new formats such as DCC (Digital Compact Cassette) and MiniDisk do permit digital transfers of both rates and thank God for that! (And Amen to that - Ed)

Interfaces - making connections


It's all very well talking about theoretical digital interfacing, but when it comes to the practical reality you'll soon discover that a variety of options exist for performing this basic function. I mean, all we're asking for is to make copies of our work or to make transfers within the digital domain, but just like any bit of gear you buy these days, it'll have jacks when you've got phonos, or XLRs when all you have is jacks.

Generally speaking, the digital format that your piece of gear uses will determine the connectors employed. The 'format' in this instance, is the protocol used to exchange the digital information, and again there are a few of these. But more on that in a moment. There are three types of connector you're likely to encounter:-

1. Coaxial


This appears on consumer and professional models and supports the S/PDIF (Sony/Phillips Digital Interface) format, often referred to as EIAJ (Electronics Industry Association of Japan). Slightly improved versions have appeared and remain compatible. Coaxial is just a fancy name for phono (RCA) connectors.

2. Optical


I've yet to see a professional DAT recorder with an optical interface. Hence, optical interfaces are almost exclusively found on consumer digital products. They are sometimes called Toslink or EIAJ fibre optic jacks and utilise S/PDIF.

3. XLR


XLR (or Cannon) connectors are used exclusively for the AES/EBU (Audio Engineering Society/European Broadcasting Union) system. This is the professional format. There's no SCMS here, just a balanced cable to transmit the digital data.

One format I haven't mentioned is the ADAT format, and the reason for that is because it is a multichannel digital audio format. Those above are just stereo, and it is here that the AI-1 comes into its own. This box allows you to use any of the above formats, in any of their interconnective guises, and perform digital transfers regardless of sample rate.

The ADAT can transmit all of its eight tracks down an optical cable but with the help of the AI-1 you select any pair of tracks, and with a BRC you can choose individual tracks too. The possibilities are breathtaking. Now you can do a truckload of vocal takes on ADAT, and then digitally transfer them to a computer program like Cubase Audio to pick out the best bits, and reconstruct a definitive vocal track. You could then EQ it on the computer and send it back to the ADAT, saving hard disk space in the process, so that you can work on more tracks.



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Publisher: The Mix - Music Maker Publications (UK), Future Publishing.

The current copyright owner/s of this content may differ from the originally published copyright notice.
More details on copyright ownership...

 

The Mix - Oct 1994

Donated by: Colin Potter

Coverdisc: Chris Needham, James Perrett

Control Room

Gear in this article:

Connectivity > Alesis > AI-1

Review by Bob Dormon

Previous article in this issue:

> Through the Square window

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