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Testing the PAQRAT: A Case Study of Computer Hell

When Rane sent me a PAQRAT for review, I hooked it up like the instructions said and tried to make a recording. Didn't work very well. Channel 1 had a steady succession of peak-overload ticks 'n pops, and the other channels all had intermittent ticks 'n pops plus some low level impulse noise in the background. This grunge was all audible when listening to the input of the ADAT, and went onto the recording as well. Definitely not 20-bit acceptable. Tom Bates, who'd dropped around to see how the PAQRAT worked, figured something was wrong with the clock in the ADAT. We tried a different ADAT. Same thing happened. Uh-oh.

We called Rane's customer support and walked through it with them, including all of the patching, etc. We all sadly concluded the unit must be defective - a serious embarrassment. Rane immediately rushed a new unit to us and we returned the offending one.

Well, I hooked up the replacement unit and got the same result. Uh-oh again. After some serious head-scratching and consultation with the publisher, I got in touch with the PAQRAT's designer, Bob Moses. We concluded that something definitely weird was going on. My ADATs all worked fine, but not with the PAQRAT. My converter worked fine. Rane knew the replacement PAQRAT was good. They'd never encountered this before, etc.

After some discussion, we decided it was time to go at this the brute force way. Bob Moses sent me a road case loaded with an ADAT, a PAQRAT, and an Apogee 20-bit converter, all patched and working. This permitted me to compare, one stage at a time, the behavior of my test PAQRAT/system versus a working reference PAQRAT/system, and to interconnect the systems as needed to figure out what was going on.

Took about an hour. Without boring you further, turns out the offending agent was the Big Remote Control (BRC). When you are using the BRC, it supplies the word clock to all the ADATs (that's how they get sample accurate sync). The provision Alesis makes for external control is a clock input to the BRC which is supposed to patch to their AI-1 A/D converter set (which I don't own, so I never bothered to read that part of the manual). Once I disconnected the BRC sync lines from the ADAT, everything worked swell, just as advertised. (Note from Dave in March, 2000: After this article appeared Alesis got in touch with me to complain about my description of the BRC as an "offending agent," and to point out that the AI-1 is not an A/D converter, but a digital audio interface. They were right on both counts, and I apologize for the sloppiness in wording here. In fact, the problem was user error - mine - I had not thought through the word clock problem. I'm older and wiser now!)

The ADAT/PAQRAT makes a Really Nice Stereo Recorder!

This misadventure really isn't anyone's fault, except maybe mine for not reading the part of the instructions that didn't apply to my system. Alesis quite reasonably never planned on the PAQRAT coming along. And, as is usual in this sort of computer hell case, when Rane checked the PAQRAT with an ADAT/BRC hookup, they did so in a rush with a borrowed BRC and everything seemed to work fine. In retrospect, they speculate that they powered up the ADAT 'n PAQRAT prior to the BRC and that the ADAT had already locked to the PAQRAT clock. Meanwhile, I've found that the BRC does not work right if it is powered up looking at some pre-loaded ADATs, but that it appears to be running OK for a while, particularly with Slave 1.

Anyway, the upshot is that you need to disconnect the BRC and use the front panel or an LRC (which comes with each ADAT even when you get a BRC) with the ADAT you're using for 20-bit. I tried taking the word-clock out of the Apogee and using it to run the BRC, but the system still didn't work. The manual says you've also got to patch the AI-1 to ADAT's optical bus and I assume that the BRC/ADAT knew it wasn't present. Whew!

The greater wisdom to be gained when dealing with digital devices and signals going between them is this: "Thou Shalt Know From Whence Thy Word Clock Cometh, or Else Thou Shalt Be Relegated To Computer Hell." The clock signal is as important as the data signal! Don't just assume it must be working OK.