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Redbone

A Place To Share Audio Files

68 posts in this topic

I guess Audio is going to be my thing.

 

I have embarked on an audio recording project, mainly because the quality of my recording efforts has been very poor for the last few years. After a lot of trial and error I think I am getting it figured out. Long story short, since I don't care about higher frequency sounds (above 1500 Hz) I have modified microphone pre-amp boards with a built in low pass filter. It allows me to clip out much of the mic and amp noise before I record it and also limits the sounds of bugs and birds. This makes the audio much clearer and easier to work with in Audacity. Now that the bugs are worked out (pun intended) i needed a place to share some of this audio. All of my stuff is battery powered and is easily deployed in the field. I'll share what I've done so it can be copied. I've also managed to do this in a very inexpensive way. That's a huge plus...

 

I'd like this thread to be a place where all of us can share audio, and discuss tips, and techniques.

I'll get started with a few clips of owls and coyotes Ive collected in the last few weeks. I will also have clear recordings of rocks being hurled at myself and my friends last week. I can't share all of it because many of the rocks triggered a barrage of cuss words, and I need to protect the location and participant's private conversations. I still have plenty to share though and will do so in the coming days.

 

For now.... here's a few clips to get us started:

 

 

This one is from a side by side mic test. It's a tree break that highlights the before and after quality of my recordings. You can really tell how much the noise has been reduced.

And... the first rock hurling incident that I can share :) (I had to bleep a bad word)

 

Edited by Redbone
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A good place to start is to explain just how these microphones and recorders work. My career is in electronics so it seemed silly that I had not delved into it earlier.

All of these portable recorders have their own internal microphones. The internal sound processing circuitry is specifically designed around this internal mic. Some have great features that allow you to customize tone and/or recording level to suit the environment you are recording in. For my purposes and on my recorders, these internal mics did not suit my needs.

 

My first step was to buy a plug in external microphone. This is where the problems begin...

These omnidirectional microphones (they get sound from every direction) are typically constructed using electret microphone elements. The benefit is that they are small, cheap, and perform reasonably well. Of course some are better than others.

Electret Construction.jpg

 

These microphones are basically capacitors that change value based on air pressure. You cannot amplify capacitance so they require an internal transistor amplifier circuit to make them give a larger electrical signal that can be sent to the recorder. For this transistor to operate, it needs a supply voltage. This voltage is fed through a bias resistor. This resistor is very necessary but it also causes a loss of potential voltage to the microphone element. (I'll explain that all in better detail if asked but it's not important at this moment)

 

Good mic elements need a few (maybe 1.5 to 2) Volts to operate. Some with better signal to noise ratios need a higher operating voltage. This is a problem. Audio recorders may differ but all of mine operate using 2x AAA batteries, that provide only 3 Volts total. The recorder will provide an internal resistor to that 3 Volt supply to power your external plug in microphone. Without going into all the silly details, I'll just say that your recorder very likely does not provide enough voltage for your good quality microphones to operate to meet the best specifications possible. You'll find some microphones have their own battery source built in. This is a great solution to that problem. If you don't want to dive into the deep end of the pool with me, you could stop here. Get powered plug in mics to replace your cheapo plug in mics and you get a slight improvement. I wanted more...

 

"More" for me, meant providing a pre-amp circuit with the microphone to boost the signal up to the same levels needed to power your headphones. This is referred as "audio In" with some recorders as opposed to "mic in". The "Audio In" setting bypasses the recorder's internal pre-amp circuit. Not every recorder allows this setting so I'm going to focus on the ones that I know can do it. It's the setting taht would allow you to plug your cell phone directly into your recorder.

 

I specifically use the Sony ICD-PX333 and I now have five of them. Sadly, they are obsolete and getting harder to come by. I pick one up every few months used from E-Bay for $30-$40. You can still find one at Amazon that includes an SD card for about $70.

 

The good news is that the newer models of Sony ICD series recorders can all do this function. I created a chart that shows the features of each. Note that the ones that record the internal mic in "mono" (not stereo) may still record in stereo mode when you use the audio in or microphone input. My ICD-PX333 does.

 

Here is the chart:

Sony Recorder Chart.jpg

 

The ICD-PX370 is a close replacement for the ICD-PX333 and is inexpensive. If you don't plan to use the internal mic, then the ICD-PX440 is extra money spent for no real benefit (that I am aware of). I am no fan of the flip out USB connector, but I also have not worn out my USB cable port on any of my recorders yet. If you use SD cards you'll always be able to access your files, even in the event of connector failure.

 

This post is already long enough so I'll continue later on....

Edited by Redbone
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Looking forward to seeing more on how you did this!  Those recordings are far better than the usual cricket symphony.

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The ol' px333. I personally have 11 of them. Not even going to guess how many our research team owns all together. It's our preferred recorder. With lithium batteries i get a solid 5 days and nights of continuous recording until the batteries die. I triangulate three of them myself with each being about a mile apart. This way i can easily tell and pinpoint exactly where within my field a sound came from. And I use the sony external stereo mic on all of them.

 

I just recently made a quick start video tutorial for people on using Audacity for Bigfoot audio research. I only made it for the new people in our research group to get them started. But I will post the youtube link here  tomorrow so it will help people on here get started using Audacity for their own audio research. It will also have some tips for those already using Audacity on cleaning up bad audio. I don't use Audacity myself, I use Nuendo 8 Pro, which is what we use in the main room in our recording studio to record bands. If i hear something good, I'll then run it through a special spectrogram software made by Izotope.

 

 

 

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I'm a little frustrated at the moment. I went and grabbed my recorder last night that I had left at the rock throwing location.

1. Something chewed the wind muff off of my microphone (i can replace it)

2. The bug symphony caused clipping. Clipping is what happens when the sound is so great that it causes the amplifier to reach max voltage. When this happens, it basically introduces strange noise at ALL frequencies that cannot be filtered out. My mics don't have a gain adjustment so fixing this may not be too easy. I left that mic in the field with a new recorder so troubleshooting will be a few days away.

 

I bought mic elements with higher sensitivity and put it on some of these. That might be the problem. There's been too much trial and error but I keep getting closer.

 

Side note: I heard two tree breaks, and movement above me up a ridge when getting the recorder. I saw "something black" although not very big. This was all followed a few minutes later by growling and a whimper. Of course I didn't have a recorder on me except the one with dead batteries that I just retrieved. I won't know if the recorder I left will have captured it because of the way it is positioned. I'll know in a few days.

Edited by Redbone
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My Project continued...

 

My goal was to find a suitable preamp to use with the clip on microphones I already had so that I could bypass the recorder's internal preamp. Early searches yielded on high end pro audio microphone preamps, which cost a few hundred dollars. That was not going to work for me. Then....paydirt!

 

There is a market for security microphones. They are made with the pre-amps built in and are supposed to be powered by a 12V DC source. It turns out that these mics work great using a 9V battery. I started with one bought on Amazon for about $8 from TNTE which is really CT-MIC002 from a Chinese company called Centro Technology. These links show a microphone with gain adjustment. They must be old pictures because there's no adjustment now. Overall these are pretty good microphones, just as they are...and cheap (cheaper in quantity of 5).

 

To use these microphones you need a 9V battery and battery cable with a 5.5mm power plug.  You also need an RCA Male to 3.5mm female audio cable/adapter. I bought a few for my testing that were more expensive than the mic, so I started making my own. Shown is the mono cable, which connects the single RCA connector to both the left and right pins of the 3.5mm cable (headphone jack style connector). I also made a few adapters that are true stereo, which takes two microphones.

 

IMG_20170928_085533270_HDR[1].jpg

 

Changing to these microphones was an improvement over the Sony clip on microphones I had been using, but still not good enough. Before I continue I'll try to dig up a few recordings that I made with these unmodified microphones.

 

I've covered this in another thread in this forum somewhere, but my field deployment setup is about as cheap as they come. I use $1 sealed drinking cups from Dollar Tree, covered in Camo Duck tape, with the mic fastened to the bottom. I used elastic hairbands to hang them (also from Dollar Tree). This setup has been tested extensively and has been found to keep my microphones dry. They are also hard to find if thought is given during deployment. I usually tuck mine behind a tree of similar diameter so that it cannot be easily noticed by anybody on the trail. I've walked people to within a few feet of one I had deployed and told them it was there and they still didn't find it.

Camo Cup 1.jpgStereo Setup.jpg

to be continued...

Edited by Redbone
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I use the slightly older ICD PX820s. I have 4 of them I think.  My research partner has the ID PX312 in between.  The only thing I've done is switch to an external Olympus mic for each.  

 

Clipping .. yeah.  I had a tree squirrel apparently sitting on top of the branch I'd connected the recorder to "go off".   It's very hard to crank the volume listening for faint things in the far distance knowing that dang squirrel chirp is coming and it's going to be so loud it pops my eyeballs out of the sockets.    Oh well ... " a (mad) man's gotta do what a (mad) man's gotta do " I often say. 

 

MIB

 

PS: thanks for the note on mics ... I'll have to look into those.

Edited by MIB
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There are several styles of these security mics. I like the one mentioned above because the mic element is pretty good. I have cheaper ones that have a better amp circuit, but have a poor mic element and poor workmanship on hand soldered parts. No problem for me because I can fix that. I've replaced the mic elements with high signal to noise ratio mics that I got from digikey. I think that may be what's causing my clipping problem. They are just too sensitive, and in my opinion the original mics are not sensitive enough. My next batch of mods will include a different mic element that is hopefully in between.... OR I need to work out a resistor change that fixes the gain, to prevent clipping. Hopefully I can find the perfect happy medium. These elements only cost about $3 apiece.

 

Here is one with heatshrink cover removed and some 'low-pass' mods in place.

They've gotten better since these pictures were taken. The newer ones use surface mount resistors instead of the axial lead 1/8 watt resistors seen below. If you look close you can see where I had to replace PCB traces with wire because I had burned the traces off trying to rework them. This one is basically scrap (even though it still works).

IMG_20170830_151404152_HDR[1].jpgIMG_20170830_151412061[1].jpg

 

Edited by Redbone
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Still at work and no time to post audio info, but here is a video I made for our research group few months ago. Audacity is okay for audio listening but it's not very good for removing noise from an audio file. It's a free download so can't expect much from it like a more costly professional audio software.. It will help anyone wanting to get started listening to their own audio. Even people already using it will find needed info on noise removal in the video also...

 

 

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I'm skipping ahead but this clip was the grand finale for our very eventful week. As this was happening  I was leading a night hike elsewhere so I was not present, but my audio recorder was hanging nearby. This all happened from 9:30 to 9:45 PM on Satiurday, Sept 23rd, 2017.

 

I do not know why these three guys decide to start chucking rocks into the water, but they did and the response was dramatic. Prior to this time they had done some knocks, whoops, and a very impressive howl. You can tell who threw each rock into the water by the response. The cussing starts only after the two rocks that came out of the forest. Because they ended in the river, we have no idea how big the rocks were but the splash was substantial. The only editing done for this audio clip was to clip out the dead time between splashes and to bleep the cuss words out. I also quieted the yelling after the 2nd response rock. The first response rock came at 9:33 and the second was at 9:45. Despite hearing them say "It's time to go" these 3 guys stayed until 10:56. My son was one of the 3.

933pm 092317 Bridge Rock.jpg

 

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I'm not going to share this sound (it's quite annoying) but here is what the spectrogram looks like when something chews the wind filter off of your microphone.

I presume it was a small rodent. This happened Monday Sept 25th morning at about 3:41 AM.

Wind filter chewed off.jpg

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Here are 3 more rock throwing incidents.

The first happened at 10:50 PM on Tuesday, September 19th. This rock actually hit me before hitting again behind and to my right (the aim was spot on).

 

This one happened the next night (Sept 20) at 11:25 PM after we did two knocks and a whoop. Another recorder also caught this audio (below)

 

This is the same rock at 11:25 on September 20th as caught on a recorder that belongs to one of the people I was with.

 

This one was 11:44PM on September 20th. My recorder was off as I was checking to see if it was still recording. Luckily another person had a recorder going. We made sure one of was going at any time when we checked our own recorders. At the time we didn't find the rock. After listening to this audio I could tell it hit a large chuck of cement below the bridge and found it there a few days later. There were no other rocks that were big enough to make this sound in that area.

 

Edited by Redbone
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note the error above. The first rock came Tuesday at 11:09 and not 10:50. The10:50 rock actually came on Friday. That's the one linked in the original post.

I'll have 4 more rock throws to share and a stick, if I can edit out the conversation happening at the time of the stick. It's not as noticeable as the rocks anyway.

 

And so I don't waste a good post only correcting my own mistake, here's a daytime knock recorded in an Iowa forest this spring (2:21 PM on 05/06/17)

This was recorded before I was very far into my big microphone project. It's just a regular Sony plug in mic. The first pass through is filtered for noise. The second pass is as it was recorded.

 

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I still have more rock throw events from a few weeks ago to share and hundreds of hours of remotely recorded audio to go through, but when squatching activity is happening and I can get out in the woods, I'm going! This owl call happened last night at 10:40 PM (central time) and followed a scream that we did about 4 minutes earlier. We were very close to it, I just wish I had shut up and let the recorder do it's thing.

1007 1040 cool owl call.jpg

 

Edited by Redbone
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Here is something crying in dark and creepy woods. This went on from 5:28 am to 5:56 on Sunday morning, October 8th, 2017.

My recorders were there for an investigation into a scream that was heard from these same woods a week earlier. Opinions? A dog and an owl can also be heard.

 

Edited by Redbone
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