The Lure Of 20-Bit Audio.

As you undoubtedly know, digital audio is made up of bits o' data. You probably also know that the dynamic range or resolution of any given chunk o' digital data (called a word) is based on the number of bits used in that chunk (word), and that each bit increases the dynamic range or resolution by 6 dB. 16-bit digital systems have a dynamic range of approximately 96 dB (6 dB times 16 equals 96 dB, get it?).

Back when analog was king, recorders with a dynamic range of 96 dB looked pretty good to us, as the best analog could do at the time was about 80 dB. However, at 120 dB, the dynamic range of our ears is still a good bit bigger than 96 dB, and now that we've gotten to take 96 dB for granted we are beginning to be bugged by the fact we can still hear a little noise in the signal. So we've begun to yearn for 20-bit systems (6 dB times 20 equals 120 dB). Such systems give us a dynamic range roughly equal to what our hearing will do. Finally!

The way you get 20-bit digital audio in the first place is to have fancier, more expensive analog-to-digital (A/D) and digital-to-analog (D/A) converters that come with 20-bit resolution. Once you have 20-bit digital audio, if you want to store it you'll need a 20-bit recorder. The subject of this review, Rane's PAQRAT, provides a comparatively low-cost solution to that problem. It allows your 16-bit modular digital multitrack (MDM) to function as a 20-bit stereo recorder.

Adapting 16-Bit Recorders To 20-Bit

A 16-bit recorder requires that you have 16 data-bits available in each sampled word you wish to store, for each channel. If you have a multitrack digital recorder, you will have multiple words available (one for each track) for each sample period. Happily, these are all neatly held in sync by the word clock.

What this means is that if you are willing to take up two tracks for one signal, you can have, in theory anyway, 32 bits o' data for each sample. All you need is a device that will look at that big 32-bit word and divide it up into two 16-bit words that get loaded on each track of the recorder. This is essentially what the PAQRAT does. Clever, comparatively simple and comparatively cheap. And it comes in two flavors, so you can use it with either ADATs (Alesis 'n Fostex) or DA-88s (Tascam 'n Sony). Cool!

Downside-wise, it reduces your eight-track recorder to a stereo recorder. Still a pretty reasonable deal if ya already own one and gotta have 20-bit.

Whatever. I think the whole concept is pretty elegant and synergistic, making use of your existing cheap raw storage capacity for a different, somewhat more advanced capability.