Ultrasonic recording?

Skytree · Post by **Skytree** » Sun May 31, 2009 5:05 pm

Does anyone here know much about recording ultrasonic sounds (sounds above the typical range of human hearing)?

I'm looking for advice on techniques and gear, if anyone can help.

I was visiting my dad for his birthday, and we ended up talking about radio, sound, etc...he mentioned playing with an ultrasonic transducer years ago with a musician friend of his. But, details were unfortunately sparse.

Any assistance would be greatly appreciated.

Cheers!

P.S. I found this link, and while it's definitely helpful, it doesn't give many specifics, either: http://www.wildlife-sound.org/equipment ... sonic.html

Cupz · Post by **Cupz** » Sun May 31, 2009 5:29 pm

Thats cool...but why would you want to record at such frequencies? I mean...I can't stand dogs...but...."

Edgar · Post by **Edgar** » Sun May 31, 2009 7:56 pm

Imagine if you recorded the ultra-sonic sound and then transposed it down to a frequency that we could hear, it might not work as well as I think, but it could be pretty interesting.

Skytree · Post by **Skytree** » Sun May 31, 2009 9:55 pm

Edgar wrote:Imagine if you recorded the ultra-sonic sound and then transposed it down to a frequency that we could hear, it might not work as well as I think, but it could be pretty interesting.

I've done this for a while actually, in a limited capacity. There are pitched-down, tempo-synced recordings of bat echolocation at the beginning of this track, from my last album. Birdsong is beautiful to do this to as well, since much of the song is above human hearing. But, I've largely been limited to sounds within the 20 hz to 40 kHz range, due to limited mic sensitivity. I want to play with the higher frequencies!

Hope this clarifies what I'm looking for. Essentially, if anyone can help me find a mic or other gear that would help with this, I'd be very grateful.

Skytree · Post by **Skytree** » Tue Jun 02, 2009 3:48 pm

Hmm...some disappointing news: My Edirol R-09 is only capable of recording at a rate up to 96 kHz. According to the ultrasonic sites I've been looking at, a good rule of thumb is that your recording setup is capable of recording frequencies up to half of the processing rate (in this case, 47 kHz). That's well above average human hearing, but not quite as high as I'd like. The built-in mic is capable of frequencies up to 40 kHz, so it doesn't seem worthwhile to purchase another mic to extend up 7 kHz further.

Ah well, worth researching at least! And now I know I can safely record sounds up to 40 kHz with my existing setup.

nurthice · Post by **nurthice** » Tue Jun 02, 2009 4:52 pm

interesting! well according to the Nyquist-Shannon theorem,you'd need a sampling rate at least twice as high as the highest frequency present in the analog signal in order to avoid aliasing. 40 kHz will give you just one octave above human hearing. If you get a transducer that goes up to 48 Khz, you won't get much more except maybe some aliasing due to higher frequencies present, since roll-off is taken as 70%, not 0..
For another octave, you'd need to go up to 80 kHz. If you can find a cheap solution with some transducer that rolls off at slightly above 80 Khz and record at a sampling rate of 192 kHz it'll probably be great. Bats can go as high as 100 kHz i think. For that you'd need some really high-tech shit though, unfortunately.
Loving Muskeg btw!

Skytree · Post by **Skytree** » Tue Jun 02, 2009 5:13 pm

Unfortunately, I can't find any cheap means to record at 192 kHz. If I'd been thinking this over before buying the R-09, I probably would have gone for something with a higher sampling rate. What I'll probably do is just continue to record at 96 kHz with the built-in stereo mics (range: 20 Hz - 40 kHz), and that should at least give me an added octave.

What would be ideal, though, is a transducer that could re-pitch the signal in real-time, which I could then monitor and record directly into the Edirol. I have no idea if such a thing exists, but it would be very cool to play with. I'd love to listen to ultrasonic frequencies live. It'd make capturing good recordings much easier as well (IE: I may not even know there are bats around, unless I can do real-time monitoring).

Anyhow, glad you're enjoying the track, nurthice!

Edit: If only I had the money! This gear looks incredible: Avisoft Bioacoustics

nurthice · Post by **nurthice** » Tue Jun 02, 2009 6:34 pm

Skytree wrote:If only I had the money! This gear looks incredible: Avisoft Bioacoustics

indeed.. the mobile recording interface looks very promising. makes me wonder why the resoltion is just 8bit / 16bit - but maybe it's no big deal?

Skytree · Post by **Skytree** » Tue Jun 02, 2009 8:57 pm

nurthice wrote:
Skytree wrote:If only I had the money! This gear looks incredible: Avisoft Bioacoustics
indeed.. the mobile recording interface looks very promising. makes me wonder why the resoltion is just 8bit / 16bit - but maybe it's no big deal?

Yeah, definitely curious...though to be fair, 8/16 bit was standard up until fairly recently. Maybe their built-in anti-aliasing filter gives them some room to bring down the resolution without compromising the signal. Check out the frequency response though: 20 Hz - 460 kHz. Damn!

Edit: Stupid pun of the day...gather 'round.

Q: Why were the audio hobbyist's recordings consistantly awful?

A: Because of their 2 bit recording setup.