It's odd how a straightforward answer to a straightforward question can throw up more questions in its wake.
I commented in 'Is there any audio quality difference between bouncing to disk and burning directly to a CD or recording to an external CD recorder?' that it is my preference to bounce a mix internally on my computer, then burn a CD, rather than record it to a CD recorder.
But that supposes that I am content with ordinary CD quality – 16-bit, 44.1 kHz in other words.
Professionally I am. My business involves publishing music to the broadcast industry, and they are perfectly content with CDs. In fact, they seem to be frightened of anything else. Mind you, it took a while to convert them from vinyl.
Artistically though, if I were making a recording to challenge Sgt. Pepper and Pet Sounds as the world's all-time classic favorite (one can dream!), then I would want to master it in the best possible format, so that it will sound at its absolute best to future generations.
Oddly, I wouldn't be so bothered about the multitrack recording system. I would regard that as an intrinsic part of the creative process, as much as guitars, amplifiers and microphones.
But when it comes to mixing into stereo, artistically I aspire to the best.
So what is the best?
One answer could be to make the multitrack recording in 24-bit, 192 kHz resolution, and mix it to that same standard.
That would have to be a pretty damn good mix, from a resolution point of view.
But something about that is making me unhappy. The mixed track that now resides on the hard disk of my computer isn't quite the same as what I heard through the loudspeakers when I was creating the mix (even assuming that the software handles the bounce perfectly).
No, the mix I heard went through a digital-to-analog converter, the mix on my disk didn't. Therefore, they are different. Not by much, but if I were aspiring to the best, then it would make me unhappy.
So what is the alternative?
The alternative is to take an analog output from the audio interface, and feed that to a very high quality stereo master recorder. Not a CD recorder of course.
And then, and here's the big thing, monitor from the outputs of that device. That way, you can hear any effect it is having on the sound quality and incorporate that into the artistic process.
So that's where the new Korg MR1 and MR1000 come in. They record digitally onto internal hard disk drives. But not ordinary digits…
They record in DSD. Direct Stream Digital.
So what is DSD? I'll answer that by explaining how conventional PCM (Pulse Code Modulation) works. I'll keep it simple…
A conventional PCM converter first samples the audio at a very high rate, typically 2.8 MHz (2.8 million times a second). For each sample, it decides whether the signal is low or high.
That results in a signal that is 1-bit, 2.8 MHz, compared to the 16-bit, 44.1 kHz of CD.
It is a mathematical fact that a higher sampling rate can compensate for fewer bits. So the quality at this point is better than CD.
Next, the signal goes through a process called 'decimation'. Silly word because it doesn't at all give the flavor of what's going on. It seems to imply that something is being thrown away. No, decimation is the process of converting the 1-bit, 2.8 MHz signal to 24-bit, 96 kHz, or whatever PCM format is required. It doesn't necessarily involve loss.
So there are two processes involved. The first is sampling, the second is decimation. That results in conventional PCM audio.
DSD does something very interesting however. It stops short of the decimation process and leaves the signal in its 1-bit, 2.8 Megahertz form. Why overcomplicate?
So arguably, DSD is the most pure form of analog-to-digital conversion one can have. And if you record that data stream, then you have the world's best digital recorder.
Granted, you can't do much with DSD other than edit it. But you don't want to do that, do you? You have created the perfect mix and you want to keep the perfect recording for posterity.
The Korg MR1 does standard DSD; the more expensive MR1000 does double-speed DSD at 5.6 MHz, making it currently one of the best possible options as a master recorder.
So with a Korg MR1 or MR1000, your master recordings are indeed ready to stand the test of time. (I wonder about the hard disk they are recorded onto though!)