Another question no doubt sparked by our 9/2 TTOTD:
“Is there any standard that evaluates the quality of A/D and D/A converters? I know that the “difference” between a low priced and a high priced DAT is in part the conversion, but what’s good? And if you’re buying a pre-amp with digital out, what’s to tell a good one from a bad one? I figure that a poor conversion DAT coupled with a good pre with digital out can give the best of two worlds… price and quality.”
Three good questions that don’t necessarily lead to the conclusion you drew. First, other than things like bit depth, sample rate, and maybe clock type there isn’t much in the way of published standards (specs) for measuring the qualitative differences between converters. In fact, it is often so tweaky, and the results so subjective that there sometimes isn’t even a direct correlation between the objective cost (quality) of a given converter and the subjective sound quality of it. Things like linearity, jitter, noise shaping, and digital filtering would reveal more about the subjective sound quality to expect, if people would publish them. But even if there were tons of published specs (which there should be, by the way) it would still be like trying to determine if a U87 or a C414 was going to sound “better.” There’s just not a clear, across the board agreement about what “better” is. As said in here before, often a big part of the difference is actually in the quality of the analog components. Traditional specs like signal to noise, distortion, crosstalk, and dynamic range are as important as ever.
At the end of the day the bottom line is ultimately, “What does it sound like?” Specs have never been an ideal way to determine this critical factor on most equipment. They only provide clues. That’s why dialing up a Web site and putting some product in a shopping basket based on its marketing hype is not always such a great idea. That’s also why we encourage our customers to speak to a Sweetwater Sales Engineer, because they get to hear and use this stuff and make relative assessments.
Another thing to consider is that companies rarely get a reputation for quality unless they deserve it. While not foolproof, this can be a great clue about what to buy. The U87/C414 example applies again. Both have an excellent reputation. You’re not going to go wrong with either one (though I would argue that if you’re serious you should have both). When it comes to converters you can look at a company like Apogee, and the reputation they have. Obviously something is going on there and if you want to be among the best you should at least check out their stuff. Aside from sheer quality, Apogee adds unique features like Soft Limit and UV22 that are worth learning about.
The conclusion about plugging a good preamp/converter combination into a cheap DAT with (allegedly) poor converters only holds up as far as the converters. There’s still a lot going on in a DAT after the signal leaves the converters. These other things are very tweaky and subtle, but making the common assumption that “once it’s digital it’s all the same” is not always safe. Not all DAT machines are equal. Some produce tapes with far more errors than others, and of course some eat far more tapes than others. These days the differences are mostly pretty minor, but for the discriminating user there are still valid reasons to spend more.