Sweet Notes Animation Q & A

Q: What is the difference between SMPTE and MTC?

A: SMPTE time code, otherwise known as LTC (Longitudinal Time Code), has been commonly used to synchronize tape decks and lots of other audio and video equipment for the past 20 years or so. With the widespread use of MIDI in the mid-1980s, a reliable method was needed to synchronize computer MIDI sequencers to tape machines (many of which already had SMPTE recorded on one tape track for other reasons). MTC (MIDI Time Code) was developed to facilitate this and for all practical purposes can be thought of as SMPTE Time Code in MIDI form.

Where LTC is an audio signal usually recorded to tape and decoded by a synchronizer, MTC is specifically for MIDI equipment and is only transmitted over MIDI. Most modern MIDI interfaces (such as a MIDI Time Piece) can convert LTC to MTC for the purpose of synchronizing your computer sequencer to tape.

Q: What is DAE?

A: DAE (Digidesign Audio Engine) was developed by Digidesign as an application that provides a foundation for digital audio recording on the Macintosh computer. This program, which runs in the background whenever you run a digital audio program on a Digidesign-equipped Mac, contains the programming code that basically provides all of the nuts and bolts for allowing software programs to interface with Digidesign hardware in the computer. The result of this common foundation is that all of the third party programmers just have to make their programs interface with this code (as opposed to the Digi hardware itself).

Since the advent of DAE people like Opcode, MOTU, EMAGIC, Steinberg, and others have had a much easier time of updating their software for increased compatibility and features as Digidesign has made hardware changes. There are quite a few different versions of DAE in use with different systems. The version of DAE (and the very important corresponding version of the Digi System Init) is specific to different kinds of hardware that you may have in your system. For example: DAE and Digi Init version 3.0 will ONLY work on PCI Macs. Never install this version on a Nubus-equipped Macintosh. For more information about specific versions, please contact us here at Sweetwater.

Q: Why do I hear about DAT machines not being compatible with other DAT machines or other equipment? I thought all DATs were the same.

A: In the early days, not all DAT machines recorded to tape in exactly the same way. This could cause compatibility problems between machines. Sometimes a tape made on a Panasonic SV3500 would not play on the Sony PCM2500 at the mastering house for example.

These days are as gone as most of those old machines, so you are probably referring to subtle differences between the types of digital inputs and outputs modern m/achines may have. There are a number of digital formats for data transfer: AES/EBU, SPDIF, IEC type II, etc. We don't really have room to go into detail about what all of these are and their differences. If you are a professional in this industry and making a living working with digital audio, it's vital to know this stuff. If you casually work with DATs and digital audio, it is usually safe to assume that if the digital connector on one DAT looks the same as the one on another DAT, you can probably transfer digital audio between them. Of course, like any good rule of thumb there are plenty of exceptions. There are also plenty of times where one can connect dissimilar connections and still get a good transfer of digital audio. The three most common types found on DAT machines are:

AES/EBU: Almost always found on an XLR connector. This is typically a balanced connection. It is considered the standard for pro studio equipment. It can sometimes be connected to other digital formats, but the results will vary. Some devices which appear to have only this kind of digital connector have software in their operating systems that can make it compatible with other formats (i.e. the Kurzweil K2000/K2500).

S/PDIF: Almost always found on an RCA type connector. This is considered the semi-pro standard and is unbalanced (cable runs must be short). Very similar to AES/EBU. but at a lower level and has additional header information present. Often a SPDIF output can be connected to an AES/EBU input with acceptable results. The AES/EBU receiving device simply ignores the extra information. AES/EBU to S/PDIF can also work, but not very often.

IEC type II: Found on a lot of Sony brand DAT machines. Customer service people at Sony can't even articulate what this really is, but for practical purposes it tends to be pretty compatible with both S/PDIF and AES/EBU going both directions. These are almost always on unbalanced RCA type connectors so they look just like a S/PDIF connection (and will usually work as such).

There are other issues and lots of exceptions to the above rules. Frankly there are instances where two S/PDIF devices cannot communicate properly. If you need to do digital transfers successfully and are about to make a purchase of a DAT or other digital device, you should consult with your sales engineer here at Sweetwater to make sure you get equipment that is compatible with the other equipment already in your studio.

Got a question? Well, we've got answers! Simply mail your question to Sweetwater at 5335 Bass Rd., Ft. Wayne, IN 46808 or send e-mail to "tech_support@sweetwater.com."