Zen & The Art of D/A Conversion Page 3

Reader's Letters in Vol.9 No.8 (December 1986) in response to the footnote question:

Thiotimoline #1 Editor: In response to JA's request for the name of Isaac Asimov's "mythical chemical substance" ("Zen and the Art of D/A Conversion," Vol.9 No.6), it is thiotimoline, a supposedly ultra-hydrophilic molecule. It was first reported in "The Endochronic Properties of Resublimated Thiotimoline," published in the March 1948 issue of Astounding Science Fiction and reprinted in The Analog Anthology #1 (Davis, 1980). Thank you for this opportunity to combine two of my interests, audio and science fiction. Now how about that free year's subscription to Stereophile?---Will Chamness Ann Arbor, MI

Thiotimoline #2 Editor: I am probably the 789th person to remind you that Dr. Asimov's endochronic substance was thiotimoline. I couldn't locate the article that first reported on it; probably it has crumbled away completely. The enclosed copy of a later article on the micropsychiatric applications of thiotimoline, however, though by now a deep yellow, could be duplicated. May you enjoy it as much as I did 33 years ago.

One reason you probably have received more answers than you really wanted is the high correlation between audiophiles and readers of science fiction. I used to read Asimov and the others while waiting for the soldering iron to heat. Then someone invented circuit boards, transistors, and computerized design, spoiling all the fun. About the same time (causal or reciprocal relationship?), science fiction went off in the opposite direction and became indistinguishable from fantasy.

Anyhow, my thanks to JA for "Zen and the Art of D/A Conversion"---incidentally, is he familiar with Pirsig's Art of Motorcycle Maintenance?---and to all of the other editors and contributors who brighten the pages of Stereophile.---A. Elgin Heinz San Rafael, CA

Thiotimoline #3 Editor: In JA's article on D/A conversion (Vol.9, No.6) he mentioned a substance which dissolved before the addition of water. The name of this substance is thiotimoline and its properties were first accurately described in Isaac Asimov's paper "The Endochronic Properties of Resublimated Thiotimoline," which was published in the March, 1948 issue of Astounding. (Asimov published a total of four papers on thiotimoline, which can be found in the following Asimov compendiums: Only a Trillion, Opus 100, Buy Jupiter and Other Stories.)

Because of the temporal extension of their carbon bonds, thiotimoline crystals dissolve approximately 1.12 seconds before the introduction of a solvent, usually water.

The most common use of thiotimoline's endochronic properties is in the construction of "telechronic batteries." The principle behind the telechronic battery is easy to understand and home experimenters will have no trouble constructing their own. A test tube containing properly purified thiotimoline is placed between a low-powered laser and a photoelectric cell. When the thiotimoline dissolves, 1.12 seconds before the addition of water, the formerly opaque thiotimoline becomes transparent and the photoelectric cell is tripped. This in turn results in water being added to another test tube containing thiotimoline. The thiotimoline in the second test tube will, of course, dissolve 2.24 seconds before water was added to the first tube. By cascading these "endochronometers" it is possible to create a telechronic battery of any desired time constant. Cascading 3215 endochronometers, for example, results in a battery in which the last tube's thiotimoline dissolves about 1 hour before water is added to the first tube.

The enjoyment of music is, of course, the end to which all audiophiles aspire. Unfortunately, most of our time is spent comparing components in order to decide which ones would give us the most enjoyment if only we had the time to listen to them in a relaxed manner. Proper use of the telechronic battery would enable us to make valid decisions without ever having to do any auditioning of the components in question.

Suppose, for example, that you wanted to decide whether to buy a dobler-smith President 5 or a David Goldblume DG20. Proper evaluation of the two components would not take more than 16 hours, including breaks. So you prepare two telechronic batteries with 16-hour time constants. Just before beginning the comparison you vow to add water to battery A if you prefer the President 5 and to battery B if you prefer the DG20. At this point the last photocell in one of the batteries will trip and you will know the results of your comparison test without ever having had to perform it. If neither photocell trips you will know that 16 hours wasn't enough time and you'd have to try again the next day.

By a modified use of this technique it would be possible for audio reviewers to evaluate equipment without wasting their time listening to the components, giving them far more time to investigate methods for taking ten paragraphs to communicate one sentence's worth of ideas.

Experimenters should be warned that thiotimoline can be dangerous. Last week, in the presence of a telechronic battery with a 10-hour time constant, I instructed an assistant to add water to the battery 10 hours hence. Because of the assistant's long history of accuracy, the last photocell tripped immediately. In an effort to show that the telechronic battery could be fooled I then locked the battery in the basement and melted down the only available key. Well, as you probably know, the Chicago area last week suffered the worst flooding in its history...---Scott Soloway Skokie, IL


hollowman's picture

(Correct me as necessary...)

The "low-pass filter" in JA's above discussion is not the "oversampling digital filter" (which is, in all reality, optional) nor is it the SAME as the output low-pass filter (e.g., analog, multi-pole).

Rather, the "low-pass filter" in JA's above discussion, is a mathematical (on-paper, or theoretical) concept of digital-to-analog RECONSTRUCTION.

To put it plainly, if all you had was a bare-bones DAC chip (take one of the first-generation CD players with a chip like Philips TDA1540) -- so, no oversampling -- the above discussion of "low-pass filter", and (sin x)/x curve and impulse response would STILL apply.

I think the confusion comes from the rather liberal way the term "reconstruction filter" is used. I.e., sometimes used as an alternate to oversampling (e.g, 4x, or 8x) ... as well as the textbook terminology (as JA notes above), or here...


(Wiki seems to suggest that the RF can ALSO be the output analog filter, e.g., brick-wall, multi-pole, etc. AFTER the DAC chip)

Again I might stand well corrected!!