Prepping Diane for the Field Season
Diane’s new post-doctoral position has to do with acoustics and sage grouse. The idea is to go to Wyoming and record noise sources and also the sage grouse themselves during the mating season. Male sage grouse display for females in a restricted area, and each male has his own small patch of territory that doesn’t have obvious food or other resources. This sort of arrangement is called a lek, and the term for having this phenomenon of males gathered into a restricted area pretty much solely for the purpose of finding a mate is called lekking.
The principal investigator on the project is Dr. Gail Patricelli at U.C. Davis. Gail had arranged last year for several custom-built “automatic recording units” (ARUs) to be available for the field season. These were to have a set of nice features: 24-bit audio capture, four channels, battery-operated, weather-resistant, using removable hard drives, able to record continuously (with a large enough hard disk), and able to be programmed to do sampling on a user-defined schedule. All of that for $2,500 a pop, a veritable acoustic bargain.
Yesterday, Diane and Gail got word from the manufacturer that the ARUs would not be ready in time for field season this year, which is now only a couple of weeks away.
So now the project needs to find audio recording systems that can do at least part of what the ARUs were going to do, and do so within a very short timeframe.
I’m helping find some options on this.
So far, we’ve identified two candidate approaches. One is to use the PDAudio sound system from Core Sound. This is a stereo 24-bit/96 kilosamples per second sound acquisition system that interfaces to a PDA via a Compact Flash slot. Taking into account the cost of a PDA, the PDAudio-CF card, the Mic2496 preamp, cables, batteries, and software, this works out to about $1,500 per unit. We got very good assistance on the technical side of things in a phone call to Len Moskowitz, the owner of Core Sound.
The other approach would be to start with a recorder and figure out how to control it to sample sound on a schedule that we set. Gail has a Marantz PMD670 Compact Flash recorder, which has a “Remote” jack. In a simple test with a microphone from an old dictation system, the recorder can be set to turn on and record when the remote is switched on, and the stop recording and power down when the remote is switched off. The difficulty here is coming up with a controller that works off of battery power and allows us to control the state of the remote jack. So far, everything we’ve found is going to require at least some basic engineering and programming, and the choices run from stuff like $30 PIC modules with battery-backed real-time clocks to a $700 touch-panel controller.
We’re trying to figure out if a TTL digital output will permit control of the Marantz remote jack, or if we need to drive a relay instead. If we need a relay, it’s just that much more that needs to be done in a short amount of time.
If anybody has a better, or at least another, suggestion, we want to hear from you. The desired daily routine would be to visit each deployed unit in the field, swap in a fresh battery, swap out digital recording media, and do whatever (hopefully minimal) adjustments that have to be made to schedule the next day’s recordings. Audio of at least 16-bit depth at 44.1 kilosamples per second needs to be recorded to removable media. We will be doing spectral analysis on the resulting data, so no lossy compression can be done on it. We will be using XLR microphone connections. The whole system needs to run off batteries, and the less massive the battery system, the better.
Update: Well, I am trying a low-tech approach. Take a wall clock. Tape a small but strong magnet to the minute hand. Affix a normally-open magnetic switch at the periphery of the clock. Wire the magnetic switch leads to a 2.5mm mono plug, which is plugged into the remote jack on the Marantz. It seems to work. The clock should run for half a year on the 1.5V AA battery. The magnetic switch needs no power. I got about a 3 minute recording on the Marantz in a test. So that’s less than 90 minutes of record time per day, and a Marantz rechargeable NiMH battery pack should handle that just fine.
