First, many thanks for taking time to read my previous post (re sense of direction--whole new idea). I am very pleased that a few people found the concept useful. Below is an extension to the idea. Dave Malham alluded to this idea (sort-of read my mind), and he also mentioned a problem that deserves careful consideration. Here's Dave's post:
**Great idea, the only problem being the presence of un-synced digital electronics near ultra sensitive analogue electronics in the microphone which would necessitate some very, very careful design to avoid interference. Might be better to develop a smartphone app that took a photo of the mic, geo-tagged it and associated that with the recorded file, perhaps via a Bluetooth link to the recorder (easy if it's a computer based one, not so easy with anything else, Apart from the environmental recordings case, the situation where it would really come in handy (at least, with an attached unit rather than a photo) is for a mic suspended on a single cable, which won't necessarily stay oriented the same way all the time due to subtle "untwisting" of the cable over time. I can vouch for that from experience of suspending mics from the central tower of York Minster. Dave** First, I'll address noise and unsynced digital signals. The device I had in mind is a passive sensor with associated electronics (mixed signal). Using mu-metal or similar shielding would preclude the sensor's ability to detect magnetic poles. The electronics, however, would be shielded. Most of the requisite electronics are tiny and battery-operated. The output signal is analog (and, of course, balanced line), so no interference issues here. Briefly, a single PIC chip could do the direction-to-frequency conversion. Diodes can easily linearize a pulse-width modulated signal, thus creating a sine wave with less than 3 percent THD. A center frequency of say 3 kHz would be 0 degrees. Compass (sensor) rotation in one direction would yield frequencies less than 3 kHz, while rotation in opposite direction yields frequencies higher than 3 kHz. The problem is 180 degrees--this could end up lower or higher than center frequency. The important idea here is that the output could be recorded on a conventional recorder (such as the TASCAM D680) without need for piggy-backing a GPS unit or other DAQ hardware needed to record time/place/orientation. However, having GPS on the recorder itself would be an asset--and would easily be isolated from microphone circuitry. Next idea (re suspended or moving mics): Just after posting my idea, it occurred to me that the analog frequency (translated to give absolute direction re Earth's magnetic poles) could also be used for error correction. I believe this may be what Dave had in mind (my apology if I'm wrong here). As a mic rotates on its vertical axis, the sensor output will inevitably change. On the recorder, this is a mere change of frequency for a continuous tone with fixed amplitude. Decoded, this change of direction can be used to compute the mic's orientation. A more sophisticated approach would entail FM: The frequency deviation provides a voltage (or equivalent bits) that is proportional to direction. The rate of change is directly related to mic's rotation frequency in rad/s (probably very slow unless you're running with the mic). Taking this demodulated frequency a step further would require linking it to Ambisonic software (A- or B-format). An 'analog' approach I had considered is to apply the direction-dependent voltage to a MIDI controller I had previously built using an Arduino board. It's a simple volume controller with an analog input (voltage), but the MIDI channel can be assigned to a panpot or other function. The panpot would be mic direction (horizontal plane). A more direct approach would be to use a mathematical expression with, for example, VVMic to 'steer' the mic to its proper orientation. I'm sure others will have better ideas--I'm simply coming up with this stuff as I write. Re GPS: Along similar lines, I had posted an idea to a forum (National Hearing Conservation Association on LinkedIn): The idea relates to noise dosimetry. My idea was to use a GPS tracker in lieu of the dosimeter worn by workers to map their locations and time spent at these locations. Fixed recordings for a variety of critical locations within a workplace could be done without need for strapping a sensitive mic / electronics to the worker. In other words, recordings and SPLs are made independently of workers being at a specific place. This could result in high-quality recordings for post-processing as well as multi-channel (or Ambisonic) recordings. When combined with 'typical' time spend in locations (a la GPS), noise dose, or Leq, could be ascertained. It wouldn't eliminate need for dosimetry, but could be useful in some situations. Thanks to everyone for your help and time. Ciao, Eric C. -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20131007/1326a0d6/attachment.html> _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
