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Respberry Pi Field Recorder
Old 27th October 2016
  #1
Here for the gear
Respberry Pi Field Recorder

First time posting but not the first time recording!!!

I am very close to completing my field recording unit. This is a hard shell back-pack setup with a Behringer 4-channel UMC404HD mixer that can output up to 192k sample rate/channel. That mixer will be connected via USB to a Raspberry Pi via running either Audacity recording at 24 bit depth or a wonderful command line program called Rotter. I have a Sound Devices USBPre 2 on order and also a set of Audio-Technica AT4022's coming within a few weeks. I will be building a few holders such as an Olsen Wing or Crown SASS hack for ambient soundscape recording.

With my rig I have tested recording at full 192k sampling-rates for the UMC404HD, over 4 channels, and am happy to report that the Raspberry Pi swallows up that data to a USB stick without missing a beat. It's quit impressive really how these little computers can handle this kind of data. Post production on the Raspberry is slow so I opt instead to bring the data over to my more capable laptop and clean it up there. I can use the command line program SOX to run spectrograms and other things as needed in the field.

My field recorder backpack has a Lilliput 7” HD monitor, connected by HDMI cable to the Pi, as a display into the Raspberry and a BlueTooth combo keyboard/touchpad to access the whole works. For power I have 2 Li-Ion battery packs at 12 volts, 9800 mAh capacity and a 180 kHz, 5 amp buck converter dialed down to 5.4 volts for USB power for everything. The interesting thing is that I can see the noise from the converter above 90kHz in spectrograms of audio data recorded at the limits of the mixer – far beyond anything I could ever record, except if I were recording bats perhaps (which I might).

All in all, I am quite excited about this portable rig. I have tested it during an 8 hour run for which I recorded only the nearly dead silence of the Behringer's pre-amps at full 192k sample rate for 4 inputs and the Raspberry swallowed it all running at about 28%CPU load using Audacity as the recorder. Part of that load was the GUI showing the waveform output in Audacity. Total amount of data recorded during that period was 23 GB. No evidence of any lost data.

I have been running a Raspberry-Rotter recorder in various locations throughout my house for quite long time now and have found that it will record without missing a beat as long as it has a stable power supply to back it up. I have captured an earthquake and a mysterious “hum” that we notice in our house but, as yet, have not been able to identify the source. The point being that these tiny little low-powered Linux computers (under 4 watts) are quite capable in this application. I ran a 30 minute test in the field recording wind rushing through a juniper tree near my home. It sounded decent despite using consumer grade CAD GXL1200's and a double wrap blanket wind-screen. I have powered this recorder for over 2 weeks straight using deep cycle batteries that I swapped out with a 3rd 7 Ah deep cycle Harbor Freight emergency car battery charger as the backup supply, and again, it recorded without missing a beat. If you feed it power, it will record whatever you throw at it.

Looking forward to some long term recording projects with this setup. I think the results will be impressive to say the least.
Old 27th October 2016
  #2
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Tommy-boy's Avatar
 

That is interesting. I wouldnot have thought of using a Raspberry as a recorder. But it sounds like you have a neat rig worked out.

Tom
Old 27th October 2016
  #3
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Recording on location

This was the setup and recording for the 30 minutes wind recording. Mic's under a milk crate with a blanket draped over the top. It worked but need better rig for Mic's.
Old 28th October 2016
  #4
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Quote:
Originally Posted by tvkas View Post
...with a Behringer 4-channel UMC404HD mixer that can output up to 192k sample rate/channel...I have a Sound Devices USBPre 2 on order...

With my rig I have tested recording at full 192k sampling-rates for the UMC404HD, over 4 channels...
Very cool.

So if you decide to record 6 channels, will you add another Raspberry 3pi; or does your type of JACK let you use multiple USB devices?

And have you tried wav32 yet?

best, john
Old 28th October 2016
  #5
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I have not thought of ever using more than 4 but now that you mention it, it does appear that it can be done with some coding to create pseudo-devices which are any mounted devices and defining inputs, etc. Normally, because I am not really a coder, I use a GUI (QjackCTL) to setup jackd to run whatever device I am using. Rotter will then run with the settings in jackd and it all just works. Now that I have both USB Mixers, I may have to try out the pseudo-device setup just to see if it can in fact be done

I have heard of Wav32 but thats about it. Not too familiar with it beyond that. I pretty much record using FLAC at 24 bit depth.
Old 29th October 2016
  #6
Gear Maniac
 

This is cool, and yet I wonder what practical advantage this holds over something like the Tascam DR-70D (or similar/better).
Old 29th October 2016
  #7
Quote:
Originally Posted by Bixby View Post
This is cool, and yet I wonder what practical advantage this holds over something like the Tascam DR-70D (or similar/better).
Well when it's not being a field recorder it can be something else...
Old 29th October 2016
  #8
Lives for gear
I'd love to see a pic of your rig in development.
Old 29th October 2016
  #9
You seem to have good DIY mojo, so here's a suggestion: Build a buck converter that can synchronize to 192 kHz (or 384 kHz if you use a clock doubler). That will alias all the switching noise to DC, where it won't bother you. You can use the S/PDIF output on your USB Pre 2 as a sync source. Convert it to word clock with a circuit like this to recover word clock from S/PDIF:
CS8416 S/PDIF decoder
One candidate for the buck converter would be the LTC3600:
LTC3600 - 15V, 1.5A Synchronous Rail-to-Rail Single Resistor Step-Down Regulator - Linear Technology
There is a demo board for this available, since you won't have an easy time soldering it yourself. Unfortunately, it's expensive, although your local FAE might comp you one if you talk a good line.

Once you solve the buck converter switching noise, you'll only have the Raspberry Pi to worry about.

David L. Rick
Seventh String Recording
Old 29th October 2016
  #10
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Quote:
Originally Posted by tvkas View Post
...
I pretty much record using FLAC at 24 bit depth.
Did you have to edit the source of Rotter to allow you to use 24 bit?

best, john
Old 29th October 2016
  #11
Here for the gear
That's actually a good question. I looked at the setups others have used for field recording and one many were doing was using a recorder as mostly a bit-box to dump and store data. They all were using a separate mixer with superior sound quality to preamp the signals and digitize it for transport to the recorder.
The Raspberry Pi that I am using does that as well but at a $35 price tag (verses $229), it suddenly becomes an attractive alternative to get in to recording without breaking the bank. In fact, Raspberry, Li-Ion Battery pack and USB memory stick all together cost ½ what the Tascam cost and exceed the capabilities of the Tascam in just about every aspect that is important to me.
So, in thinking about it here are the benefits I like about my setup:
  • I made it myself – that is jut cool and gives me a sense of accomplishment.
  • Massive storage!! I have a 256 GB USB stick I am using currently. That is double the listed maximum specifications for the Tasam's memory expansion. If I wanted, and provided I could power it, I could record terabytes on an SSD. That probably doesn't matter to most people but I do like to do long term, unattended recording.
  • Battery life – I have run for 8 hours on one of my battery packs and I have 2 of them that I can parallel. I have set up deep cycle batteries that will run for weeks at a time.
  • Format, bitrate and depth – I can record to practically any format I want at up to 320Kb/sec and from 1 to 192k sample rate. I have sampled at 400 Hz for extended time periods – makes really nice small files for those times when I only want to hear/see frequencies below 200 Hz like seismic and atmospheric noise. Being able to record at 192 kHz is a plus for the times I want to be able to record bat sounds, which I want to do.
  • I have a GUI – I can see the audio being recorded as it is being recorded. My mixer has lights, yes but, for me, seeing the audio waveform spool out before me is a plus.
  • Everything is there, I have all of my normal audio applications that I use on my laptop right there on the Raspberry. So, if I want to run a spectrogram on a sample of sound, I can do it. Who doesn't want to run a spectrogram out in the field???
  • If I get bored of doing this, I can indeed re-purpose the Pi and turn it into a garage door opener.
Old 29th October 2016
  #12
Here for the gear
Quote:
Originally Posted by jabney View Post
Did you have to edit the source of Rotter to allow you to use 24 bit?

best, john
I have not edited Rotter to do that. I am a very novice coder - I really do not have that skill level. Rotter really is not the recorder but rather is the controller/interface into JACK and whatever storage medium you have. All settings for JACK, which ROTTER calls to record, can be set using something like QJackCTL - a GUI for the JACK command line audio program. You can also write your own jack settings file.

I use QJackCTL to set up my audio device and I can use ROTTER once that is all running. Rotter doesn't seem to support anything other than 16 bit or 32 bit float. I use Audacity for the 24 bit stuff but it would be interesting to get ROTTER to do some 24 bit work.
I might have to take a look at this and maybe expand my coding abilities.
Old 29th October 2016
  #13
Here for the gear
Quote:
Originally Posted by David Rick View Post
You seem to have good DIY mojo, so here's a suggestion: Build a buck converter that can synchronize to 192 kHz (or 384 kHz if you use a clock doubler). That will alias all the switching noise to DC, where it won't bother you. You can use the S/PDIF output on your USB Pre 2 as a sync source. Convert it to word clock with a circuit like this to recover word clock from S/PDIF:
CS8416 S/PDIF decoder
One candidate for the buck converter would be the LTC3600:
LTC3600 - 15V, 1.5A Synchronous Rail-to-Rail Single Resistor Step-Down Regulator - Linear Technology
There is a demo board for this available, since you won't have an easy time soldering it yourself. Unfortunately, it's expensive, although your local FAE might comp you one if you talk a good line.

Once you solve the buck converter switching noise, you'll only have the Raspberry Pi to worry about.

David L. Rick
Seventh String Recording
This is very good information. Although the only place I can actually see the buck converter noise is when I record at 192kHz - the spectrogram shows a nice line right at about 92 kHz. I have not even thought about any additional noise beyond that. Certainly I do not see any other noise lines in the spectrograms, even when recording nothing but silence. I have thought to add a simple common mode filter to my buck converter. The one I am using is HERE. It fits nicely into the battery pack case and for my load runs cool.

This I will definitely have to look into - it will be my next upgrade to this project.
Old 30th October 2016
  #14
Gear Addict
 

Raspberry is pretty amazing and has plenty of power to do a lot of audio related tasks for a ridiculous low price. I always wonder why not more people utilize it here.
Old 30th October 2016
  #15
Here for the gear
 

Interesting idea - I already use an RPi for audio streaming

One question - is the idea of the SD USBPre2 for when you only need 2 inputs rather than 4? Interested as I already own one of these also and not thought about plugging it into the RPi!
Old 30th October 2016
  #16
Here for the gear
 

Another question - have you considered whether it's worth including some kind of USB power conditioner between the Behringer and the RPi? Not sure such devices are necessary myself but there are a number around, eg:

A Collection of USB Audio Enhancement Products | AudioStream
Old 30th October 2016
  #17
Here for the gear
I got the SD USBPre really based on recommendation of other field recordists. It has a reputation for being a very clean preamp and so far in the few minutes I got to play with it I am not disappointed. That plus the various outputs it has works very well with the already made field recorders. The Behringer seems to also have pretty clean preamps and the 4 inputs will make it ideal for recording comparisons on different boundary mic configurations. I can't afford (yet) to get 4 AT 4022's so I may opt for a much cheaper alternative like 2 more of the CAD GXL1200's I currently have. They are noisier but that will be fine for comparing boundary configurations.

In thinking about it, I may even be able to compare the sound of the SD's preamps with the Behringer over S/PDIF just to see if there is a great difference. I got the Behringer on eBay for $120 if I remember. The SD was much more!

As for USB filters, I have spent many hours researching many different devices and I have read many articles that express support for them and others that suggest that they do absolutely nothing at all because USB is digital, not analog. So, for now I am going to wait before looking into these items because I need more experience recording and processing audio to find issues with the sound that these devices might solve.

Besides simple common mode filtering that I will be doing for now, I will only be investing in David Rick's suggestion of synchronizing the power supply with the preamp - this one thing will do more than anything else to mitigate power supply caused noise. I had read about this previously but didn't pay too much attention until he mentioned it and suddenly I got it - so I will get it.
Old 30th October 2016
  #18
Gear Addict
 

All the golden USB cables and other snake oil stuff is *mostly* a waste of money. In the end it's just ones and zeros.
Old 31st October 2016
  #19
Gear Addict
Wondering if the 'zita-j2n' tool works on raspberry pi.
Then a pi could be used to transport the [multichannel] audio over a local network (works fine with regular pc's).
Old 2nd November 2016
  #20
Here for the gear
Spectrogram

I ran a spectrogram comparing the audio from the Behringer and USBPre2 just to see what things look like. The test is very subjective, not quantitative in any way. I discovered a few things.
  • The Behringer exhibited less apparent noise than the USBPre2. This may be because the USBPre2 has greater amplification capabilities. Further testing will need to be taken here.
  • The USBPre2 has some sort of issue I have not been able to sort out in that it has a low click or low pop that appears occasionally. It may be a power supply issue but I have seen it on both my laptop and on the Raspberry.
  • The USBPre2 has a remarkably even noise profile. It's not heavier on the low end like the Behringer.
  • The USBPre2 is a class compliant device so in Linux it will only sample at 48k @ 24 bit depth or less. This despite the fact that it can be manually set to other sampling rates. This was something I did not know when I bought it.
  • The Behringer will sample up to 192k in Linux.
  • The Behringer does not have S/PDIF output. The only digital output is USB.
  • The Behringer has noise bands that do not appear in the USCPre2. They are outside the sampling band. This may be power supply noise.
Attached Thumbnails
Respberry Pi Field Recorder-test.png   Respberry Pi Field Recorder-pop.jpg  
Old 2nd November 2016
  #21
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Quote:
Originally Posted by tvkas View Post
I ran a spectrogram comparing the audio from the Behringer and USBPre2 just to see what things look like. The test is very subjective, not quantitative in any way. I discovered a few things.

...
[*]The Behringer has noise bands that do not appear in the USCPre2. They are outside the sampling band. This may be power supply noise.[/LIST]
Have you tried using the Behringer UMC404HD without its power supply (using one of the USB ports on a computer more powerful than the Raspberry Pi), and then taking your measurements?

I didn't try all 4 inputs at one time, but one input of the UMC404HD with a Shure Unidyne III (it's like an SM57) into a Mixbus 3 at 48k worked for me. And it made some decent noise powered only by an HP Workstation USB port, (if I remember correctly). Of course you're not supposed to do that. But it did work - IIRC.

best, john
Old 3rd November 2016
  #22
Gear Addict
 

Holy cow this is fantastic!

I'd never heard of Raspberry Pis, but you just sent me on a long, fruitful journey.

I'm intrigued with this on so many levels (not all to do with remote recording...but that's OT...), but as it pertains to recording, I think this is so worth pursuing.

I would LOVE to see some picturs of your setup; your Raspberry Pi enclosure...etc.

Have you looked at the 7" touch screen that integrates with the RP? It integrates physically, and is connected via ribbon cable.

If I understand correctly, any USB A/D converter should work on this...correct? So my USBPre2 should just plug right in and mount?

Also, I'd love to know which brands and models of parts you used for your power supply. I've been looking at the Remote Audio system, but I know there are less expensive options, like the RAVs I think.
Old 4th November 2016
  #23
Here for the gear
Quote:
Originally Posted by jabney View Post
Have you tried using the Behringer UMC404HD without its power supply (using one of the USB ports on a computer more powerful than the Raspberry Pi), and then taking your measurements?

I didn't try all 4 inputs at one time, but one input of the UMC404HD with a Shure Unidyne III (it's like an SM57) into a Mixbus 3 at 48k worked for me. And it made some decent noise powered only by an HP Workstation USB port, (if I remember correctly). Of course you're not supposed to do that. But it did work - IIRC.

best, john
I have only powered both mixers from USB only - the USBPre2 is only powered by USB anyway, there is no external power. As an addendum to the testing I have done, the USBPre2 is a vastly superior product to the Berhinger. As I suspected, with the mixer turned all the way up the Berhinger is noisier and sound levels not as loud. The USBPre2 is far, far less noisy!

As for how I power the Field Kit - a Li-ion 12volt 9800 mAh power pack feeds a 180 kHz buck converter set to about 5.4 volts. That is routed to an 8 port USB hub. I have run a few different configurations with that and what I find is that it seems to work better plugging the mixer into the Raspberry directly and power the raspberry from the USB hub so that the raspberry and mixer talk directly with no middle man. I plug the memory stick in the Raspberry as well.The only other things I might plug into the hub is Keyboard or mouse on the rare occasions I need them. Most times I can remote into the Raspberry and do whatever I need or, in the field, a bluetooth mini keyboard/trackpad does the trick.

One thing is for sure, and now that I have 4 mics I can fully test, is that the raspberry will handle all 4 inputs at 192k sample rate and not miss a beat. The USBPre2 only has the 2 inputs and, as mentioned earlier, on Linux will only sample at 48k and that works fine.... except for one little bug I noticed, an occasional "click" in the right channel when recording. I am pretty sure it's a transport issue but I am still testing that. I have been sitting listening to the output through headphones with the USBPre2 powered directly by the hub and with nothing else running (the Pi isn't even plugged in). It's just headphones and preamp and mics. In this test everything seems to be performing flawlessly. I have heard the right channel click on both my laptop and on the raspberry.

I have an older Raspberry 2 recording in my basement running as a simple geophone recorder. Basically, it's an inertial seismophone being sampled at 8k using ROTTER to record the data. It easily picked up the compression roller in front of my house as they were grading the road. Cool!!
Old 4th November 2016
  #24
Here for the gear
Quote:
Originally Posted by pieter k View Post
Holy cow this is fantastic!

I'd never heard of Raspberry Pis, but you just sent me on a long, fruitful journey.

I'm intrigued with this on so many levels (not all to do with remote recording...but that's OT...), but as it pertains to recording, I think this is so worth pursuing.

I would LOVE to see some picturs of your setup; your Raspberry Pi enclosure...etc.

Have you looked at the 7" touch screen that integrates with the RP? It integrates physically, and is connected via ribbon cable.

If I understand correctly, any USB A/D converter should work on this...correct? So my USBPre2 should just plug right in and mount?

Also, I'd love to know which brands and models of parts you used for your power supply. I've been looking at the Remote Audio system, but I know there are less expensive options, like the RAVs I think.
If you know a little Linux then this is the geek project for you. If you know Windows, there are little mini computers out there that also run windows but they are a little more expensive. I'm good with Linux so this was the best option for me.

I have recorded with any number of sound cards and self powered microphones. Most are crap – even my USB powered Yeti Blue has garbage for sound compared to a pair of AT4022's hooked up to the SD mixer! What a difference.

I did see the touch screen but opted for the 7” HD display because it was totally self powered and did not increase the current draw of the Raspberry. Once recording starts, I power it off, walk away and come back when I am done. I may investigate one later but with the raspberry powering the mixer directly, I prefer to keep it's workload down as much as I can.

The power module is available on eBay for about $6 for the one I got. In testing I cannot hear any noise or see any noise below 80khz from it in spectrograms. For now that is good enough for me but, as mentioned in a previous post, a better option would be to synch the power supply to the mixer for the cleanest results. The battery box was also an eBay find that I modified to put the buck converter in the case and run a cord out from there to the USB hub. You can search

Yes, if you have a USBPre2, you should be able to simply plug it in and start recording with something like Audacity. That is what I am using currently when I am not using ROTTER, which is a little more complicated and requires command prompt entries. I have those in a text file that I can copy and paste to speed things along. You can also create a menu item to start something like that going.

2800mAh 6800mAh 9800mAh DC Rechargeable Li ion Battery Pack for 12V Devices | eBay – Battery Pack
DC to DC 4V-38V to 1.25V-36V 5A Step Down Power Supply Buck Module 24V 12V 9V 5V | eBay – Buck Converter

I just finished up my first boundary mic holder and it actually works pretty good. It is sort of a combination of an Olson Wing and Jecklin Disc. I got the idea from a site that showed a cardboard box, called a BriniBox as a stereo boundary setup and THAT worked, but was too big for my liking and cardboard would seem to absorb some sound energy. So I combined all into one wooden project. It was crudely put together with glue oozing out of the seams and all but it actually worked! I'll post pictures of that once I get a better set-up going for that. It's a good start but I have more ideas to pursue in this area.

In the attached pictures is the whole thing running out on some property we own. The mic's are under a milk crate and are just sitting a few inches apart. The recorder is about 20 feet away safely tucked away in the hard shell backpack case. That has a rain-fly so if it was nasty weather, it could still run. Think stormy weather!!
Attached Thumbnails
Respberry Pi Field Recorder-fieldkit.jpg   Respberry Pi Field Recorder-s-l1600.jpg   Respberry Pi Field Recorder-raspirec.jpg  

Last edited by tvkas; 4th November 2016 at 07:37 AM.. Reason: Ad picture
Old 4th November 2016
  #25
Gear Addict
 

tvkas, thank you. This is such excellent stuff.

Admittedly, my interests here--and seeing what you're recording (sub-audio and supra-audio with varying sample rates; i.e., construction vibrations and bats)--are leading me to places outside of the bounds of this forum, but this is hugely inspirational, unorthodox stuff...and it's great.

Let me see where this leads me and I will report back with development.

I'm surprised there isn't more interest here in the solutions you're proposing, even if for no other reason due to economy.
Old 4th November 2016
  #26
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Quote:
Originally Posted by pieter k View Post
I'm surprised there isn't more interest here in the solutions you're proposing, even if for no other reason due to economy.
Speaking only for myself, I am an old fart who has overcome his addiction to soldering irons. I built some nice gear but now I just listen to it. ;o)
Old 5th November 2016
  #27
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Tvkas's Brinibox is by Dave Brinicombe an ex BBC recordist
Dave had many devices, an auto start Nagra than ran when the Camera produced Neopilot, and the origins of Rycote high wind covers and Hairys
Its amazing what tinkering with cardboard can produce with a fertile mind.
Old 5th November 2016
  #28
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Credit where credit is due

Quote:
Originally Posted by Rolo 46 View Post
Tvkas's Brinibox is by Dave Brinicombe an ex BBC recordist
Dave had many devices, an auto start Nagra than ran when the Camera produced Neopilot, and the origins of Rycote high wind covers and Hairys
Its amazing what tinkering with cardboard can produce with a fertile mind.
That's correct - I fell on his web site when I was researching boundary and pressure zone microphones for soundscape/earthscape recording and I thought it was brilliant. I saw all the designs sort of come together at once and I definitely wanted to give him credit for the inspiration he gave me - I did link his web site.
Old 5th November 2016
  #29
Here for the gear
Quote:
Originally Posted by pieter k View Post
tvkas, thank you. This is such excellent stuff.

Admittedly, my interests here--and seeing what you're recording (sub-audio and supra-audio with varying sample rates; i.e., construction vibrations and bats)--are leading me to places outside of the bounds of this forum, but this is hugely inspirational, unorthodox stuff...and it's great.

Let me see where this leads me and I will report back with development.

I'm surprised there isn't more interest here in the solutions you're proposing, even if for no other reason due to economy.
Pieter,

What REALLY got me started in this was a desire to actually record the Schumann resonances. I was surfing the interwebs, looking at nothing in particular, when I came upon a web site about this phenomenon. I never knew such a thing even existed. There are dozens of web sites where people made antennas and recorders that would work for a few hours or maybe a day, but not much longer. I started thinking that with a Raspberry, I could record that to a USB stick and while I was at it, I could add to that a small seismometer to see if there are any precursors to earthquakes that I might be able to detect or if the propagation of Rayleigh/Love waves can induce a piezo response that could be picked up. I found designs for the antenna and a super simple seismometer and all the while I kept thinking “I wonder what the Schumann resonances sound like?”

I haven't made that antenna yet – too difficult to find the very high permeability iron I need for the core material. But I am dreaming of the day I can record it and listen to it and perhaps even share it with whomever wants to listen. That's what drives me now – the wonder of what it sounds like.

The inspiration for me to record in general came from a most wonderful book called Pulse of the Planet by Jim Metzner. You may have heard of him from NPR where he used to play a daily sample of something he recorded. Anyway, I found his book in a store and it had a CD in it. Each track had it's own chapter in the book that you could read about the recording. He describes using something like a using a phonograph cartridge to record leafcutter insects – brilliant!! If you can find this rare book, GET IT! Listen to it. It will open doors to expanding creativity.

https://en.wikipedia.org/wiki/Schumann_resonances
Pulse of the Planet : Sounds of science, nature and culture
Old 5th November 2016
  #30
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