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I was messing about with contact microphones last year and very much akin area to guitar amps as high-impedance, so very much the same issues. If you run on ba
by Zenst 5y ago
I was messing about with contact microphones last year and very much akin area to guitar amps as high-impedance, so very much the same issues.
If you run on batteries you will find it works best, as with anything mains, you will want a good ground.
What I did find was that if you use peizo's back to back you can effect a balanced signal and that in itself helps immensely in eliminating much of the noise. You can also use a contact material sandwich in-between the piezo discs and effect how it works tone wise as well as become more zoned in the pick-up area.
But impedance matching is, as with guitars, very much key for pre-amps.
As for input levels and clipping - the rise of 32bit float has made a huge difference and means you can not worry about mic input levels at the ADC stage as much and normalise everything in post, sorting the levels out then without any fear of clipping at all.
Some nice low-noise preamp designs to check out here: http://www.richardmudhar.com/piezo-contact-microphone-hi-z-amplifier-low-noise-version/ http://www.richardmudhar.com/piezo-contact-microphone-hi-z-a...
Though those just unbalanced input designs, alas I'm not aware of any balanced contact mic's on the market - but can easily make them yourself using the above approach.
- klodolph 5y agoOne common solution for piezo pickups / contact mics is to put an amplifier or buffer near the pickups, powered by a 9V battery or 48V phantom power. The piezo pickup is not balanced but it's not necessary, you can make the output of the amplifier balanced. This is the same way that condenser mics work. The microphone capsule itself is not balanced, but it doesn't need to be... the output of the amplifier or buffer is balanced and that's all you need.
- michael1999 5y agoWait. We have ADCs that produce floats now? That’s amazing.
- Zenst 5y agoYip - not looked into any IC's, though kit with that functionality been trickling past couple of years and slowly picking up pace. https://zoomcorp.com/en/us/field-recorders/field-recorders/zoom-f2/ https://zoomcorp.com/en/us/field-recorders/field-recorders/z... one example.
- KeytarHero 5y agoNot exactly - Zoom stuff does a clever trick of using 2 ADCs at different gain levels (essentially the same way that HDR photography works), but ultimately it's still using fixed-point ADCs. This isn't actually a new idea - I know Line 6 has been using it in guitar pedals since at least 2006. Of course, ADCs have gotten better since then - I doubt they were getting even 24 ENOB back then.
- Zenst 5y agoAh the F6 has dual ADC and it uses that to cover a larger recording range - best explained here https://www.youtube.com/watch?v=NTuJ1fk3PsY https://www.youtube.com/watch?v=NTuJ1fk3PsY Also nicely explained by Sound Devices here for their offerings: https://www.sounddevices.com/how-is-a-32-bit-float-file-recorded/ https://www.sounddevices.com/how-is-a-32-bit-float-file-reco... Still pondering the F2, does it have dual ADC to capture that input range or is this why they sell it with a lavier mic included (hmmm).
- ansgri 5y agoIt seems we do not, not quite. A quick googling got quite a few research papers and prototypes, but nothing mass-produced.