Buying a cable to record ATC/intercom off GoPro

[ainokea]

What I am going to try is just sticking a small mic inside my headsets. I have the pricey cable and the setup you are putting together is basically the same thing. The problem is that you get ATC but no outside engine noise (see my KTMB landing on my YT). I would like to have some engine noise for "atmosphere".

Stick the mic in your ear cup and you'll get the engine noise and all of your dialog between you, ATC, and your passenger. You can turn your headset volume up in that ear where you stuck your mic if you want the dialog to be louder.

 

[Palmpilot]

But isn't the issue that the output from the panel that drives the headset is designed for high impedence = higher power than the camcorder can handle or ???

I'll try to make this understandable without making my EE colleagues on the board gag.

My headset's impedance is in the neighborhood of 600 ohms, so the impedance of an aircraft audio panel's headphone output would be in that ballpark. (The spec sheet for my headset says that it will work with a source impedance anywhere from 150 to 1200 ohms.)

The camera microphone inputs that I've dealt with have all been higher impedance than that, in the thousands or tens of thousands of ohms.

Usually, higher impedance does not equal higher power. Power is roughly the voltage squared divided by the impedance. (I say roughly because phase angles also enter into it.) Engineers usually use a low impedance circuit when they need to deliver significant power to a load, because it takes less voltage to produce the amount of power needed, and less voltage solves some design problems. That's why loudspeaker impedances tend to be in the 4 to 16 ohm range. Headsets don't need as much power as loudspeakers, which is why it's practical to use an impedance around 600 ohms.

It's true that the audio panel is designed for higher power than a microphone input needs or can handle, but when a low impedance output sees a high impedance load, it simply delivers less power than it is capable of. On an emitter follower output circuit, for example, the output transistor usually doesn't care what load impedance it sees as long as the power delivered is not greater than the output circuit is designed for. However, if you encounter an output circuit design where that is not true, that's where you would need to put a load resistor or a headphone in parallel with the microphone input of the camera.

 

[denverpilot]

http://www.barnstormeraudio.com/IRC.html

The IRC0014 series intercom recording cables addresses the problem of attempting to use a standard microphone interface to record a signal intended to drive a 600 ohm aviation headset. The integrated electronic circuitry steps the signal down to levels expected by the recording device, preventing oversaturation of the recording device and thereby eliminating any distortion.

Additional protection is provided via AC coupling, ensuring that only the audio signal is passed while DC power remains isolated to the respective equipment. At low levels, DC power interference can reveal itself as a high-pitched squeal in the recorded audio. If enough voltage is present, irreparable equipment damage can occur

So a $.10 resistor and a $1.20 1:1 audio transformer biscuit. In low quantity. Could stock 100 of each at a time and get that biscuit transformer below $1.

Impressive description for $1.30 worth of components.

I love Marketing.

 

[alfadog]

I'll try to make this understandable without making my EE colleagues on the board gag.

My headset's impedance is in the neighborhood of 600 ohms, so the impedance of an aircraft audio panel's headphone output would be in that ballpark. (The spec sheet for my headset says that it will work with a source impedance anywhere from 150 to 1200 ohms.)

The camera microphone inputs that I've dealt with have all been higher impedance than that, in the thousands or tens of thousands of ohms.

Usually, higher impedance does not equal higher power. Power is roughly the voltage squared divided by the impedance. (I say roughly because phase angles also enter into it.) Engineers usually use a low impedance circuit when they need to deliver significant power to a load, because it takes less voltage to produce the amount of power needed, and less voltage solves some design problems. That's why loudspeaker impedances tend to be in the 4 to 16 ohm range. Headsets don't need as much power as loudspeakers, which is why it's practical to use an impedance around 600 ohms.

It's true that the audio panel is designed for higher power than a microphone input needs or can handle, but when a low impedance output sees a high impedance load, it simply delivers less power than it is capable of. On an emitter follower output circuit, for example, the output transistor usually doesn't care what load impedance it sees as long as the power delivered is not greater than the output circuit is designed for. However, if you encounter an output circuit design where that is not true, that's where you would need to put a load resistor or a headphone in parallel with the microphone input of the camera.

Boy, you do keep things complicated.

How can an output have an impedance? I thought impedance was the AC analogue to resistance in a DC circuit. In DC, output is volts, amps is dependent on the resistance of the "receiving" circuitry, I=E/R. I would not say the "impedance of an aircraft audio panel's headphone output", I would say an audio panel that delivers a range of potential (voltage) designed to drive headphones of a given impedance or impedance range.

Do I have it wrong, there?

When we talk about a speaker, we are talking about the power required to move a magnet of a given mass that will move a given mass of air so as to create a sound. More air moved, more sound. It takes a given amount of power to move a given mass of air at a gven frequency.

You did not address my speaker question: If I have a speaker with 8 ohm impedance and one with 80 ohm impedance and connect them to a simple splitter off the same mono audio source, won't one sound a lot louder than the other?? The 8 ohm would be louder, no?

So how would that same affect recording into a camcorder with an output designed to drive the headsets of different impedance?

 

[bkspero]

You did not address my speaker question: If I have a speaker with 8 ohm impedance and one with 80 ohm impedance and connect them to a simple splitter off the same mono audio source, won't one sound a lot louder than the other?? The 8 ohm would be louder, no?

So how would that same affect recording into a camcorder with an output designed to drive the headsets of different impedance?

If the signal source was capable of delivering all the current needed to drive the 8 ohm load, then the 8 ohm speaker would be louder at equal output voltage. If the signal source was only designed to provide enough current to feed the 80 ohm load at peak voltage, then you would likely damage the signal source if you tried to drive the 8 ohm load at near peak output voltage.

The camcorder problem, I believe, is less one of impedence matching and more one of matching input signal levels (voltages). If the recording device has a line level input it is designed to operate at relatively high signal levels and I think people have relatively good success recording from their panels with simple cables to adapt the connections. Audio recorders typically have such inputs.

However, if the recording device has a microphone level input (such as my camcorder does), it is designed to accept much lower voltages than an audio panel will normally output, and it will be overdriven to distortion (and possibly damage) unless there is some circuitry in the camcorder or cable to lower the voltage to an acceptable level.

Earbuds are pretty inefficient microphones, so they output relatively low signal levels and may require that the sound level be relatively high to drive even a mic level input well. They will not, I believe, provide enough signal to drive a line level input. Fortunately our cabins are noisy enough that sound levels are pretty high even inside an earbuds with 30 DB sound attenuation.

 

[Palmpilot]

Boy, you do keep things complicated.

I wish I knew how to make it simpler!

How can an output have an impedance? I thought impedance was the AC analogue to resistance in a DC circuit. In DC, output is volts, amps is dependent on the resistance of the "receiving" circuitry, I=E/R. I would not say the "impedance of an aircraft audio panel's headphone output", I would say an audio panel that delivers a range of potential (voltage) designed to drive headphones of a given impedance or impedance range.

Do I have it wrong, there?

Outputs do have impedance. That's what my headset's spec sheet is referring to when it says that it works with a source impedance anywhere from 150 ohms to 1200 ohms.

I'll try to explain what is meant by the term "output impedance" (which is synonymous with "source impedance").

If the output of the aircraft's audio panel were an ideal voltage source, then the output voltage would be the same regardless of the load impedance. However, in real life there is no such thing as an ideal voltage source. Output impedance is a measure of how the output voltage changes when the impedance of the load changes. If you measure how the voltage changes when you connect a known load resistance to an output, then you can calculate the output impedance.

When we talk about a speaker, we are talking about the power required to move a magnet of a given mass that will move a given mass of air so as to create a sound. More air moved, more sound. It takes a given amount of power to move a given mass of air at a gven frequency.

You did not address my speaker question: If I have a speaker with 8 ohm impedance and one with 80 ohm impedance and connect them to a simple splitter off the same mono audio source, won't one sound a lot louder than the other?? The 8 ohm would be louder, no?

I agree, and since the 80 ohm speaker is not as loud as the 8 ohm one when driven with the same voltage, that means that the power delivered to the higher impedance speaker is lower.

So how would that same affect recording into a camcorder with an output designed to drive the headsets of different impedance?

The microphone input of my camcorder had a much higher impedance than headsets do, and I'm assuming that camcorders are still designed that way, because using a low impedance microphone would introduce other design problems. So, just like with speakers, the power delivered to the higher impedance load (the microphone input) is much less than the power that would be delivered to the lower impedance load (a headset).

Of course, bkspero is correct in saying that for a microphone input, the important thing is to get the voltage in the right range. He thinks that the voltage a headset sees would be too high for a microphone input. I don't remember doing anything to reduce the voltage when I made video recordings in the cockpit, and there is no noticeable distortion on the recordings. However, this was probably fifteen years ago, so it's possible that I could be remembering the connection details wrong.

 

[flyingcheesehead]

Hi. I just tested a pair of iPhone earbuds as mic by recording while:

1. holding the earbuds quite close to my mouth to simulate being inside a headset and speaking quite loudly.
2. Speaking the same tone into the laptop mic which was almost two feet away.

The laptop mic, even though 20x distant, recorded quite a bit louder. Obviously it takes a lot less energy to drive the dedicated mic than to reverse-drive the earbuds.

Is that your experience? Does inceasng the volume in the edit process cause distortion issues in the finished vid?

Thanks

Doesn't surprise me, as headphones are designed to be optimum for sending sound, not receiving it... But I've never had to make any adjustments to the levels to make it sound good, either. (See post #7 in this thread.)

 

[flyingcheesehead]

Why do you want engine noise in there?

Which would you rather listen to:

(Dedicated cable)
Tower: "Diamond 9DS, runway 32, cleared for takeoff."
Me: "Cleared for takeoff runway 32, 9DS."
*a minute of nothing but silence*
Tower: "9DS, contact departure."

(earbuds/mic in headset)
Tower: "Diamond 9DS, runway 32, cleared for takeoff."
Me: "Cleared for takeoff runway 32, 9DS."
*engine revs a little as I pull onto the runway*
*engine moves up to full throttle as I begin the takeoff roll*
*Tire noise increases*
*air stream noise increases*
*Tire noise goes away as I lift off*
*engine pitch decreases a bit as I pull the prop back*
*flap motor adds a subtle whine as I retract them*
Tower: "9DS, contact departure."

The first one is very sterile. It's not much fun to listen to. The one with the engine/tire/air noise will be EXACTLY what you heard when you were flying the flight, thus it's much easier for your listeners to put themselves in the cockpit with you and a lot more fun to listen to.

 

[denverpilot]

I plan on doing a proper mix down to include both "ambient" sound and direct intercom sound in my videos this summer.

 

[alfadog]

Doesn't surprise me, as headphones are designed to be optimum for sending sound, not receiving it... But I've never had to make any adjustments to the levels to make it sound good, either. (See post #7 in this thread.)

Well, I can certainly give it a try next time I fly. I also do not particularly like just straight audio panel. It is better than overdubbing Kenny Loggins, though. By a lot.

 

[CRAZEDpilot]

Wow you guys make things sound so complicated to save $20. :wink2: We sell a similar cable - it uses a circuit board to match up the impendence difference and protect the aircraft COM system. The big question the OP asked was "why is $40SOME dollars so necessary"?

Part 'quality' and part 'risk':

1. This is a matter of personal taste, but if you wish to use your audio for anything semi-quality, a good manufactured cable with a proper circuit design and shielded wire in an electronically noisy invironment (RF) will yield the BEST results. Fred, a recent customer, just sent us an email claiming it's a "..much better sound clarity than my cobbled-together Radio Shack solution". When impedance is properly matched the levels
in the audio are near perfect, without being distored from overdrive.

2. Stabbing custom cabling into a $3000 com system in a rental plane (or any plane) is not worth the risk of damage if you ask me. Using factory soldered and tested cables is much safer - that's why I use one of our own cables for audio recording.

I really think the risk point is the biggest point that hasn't been covered here. I'm sure it's debatable, but the fact is no one is as good at custom wiring a cable as a manufacturing team - what would you tell your FBO (or your wife) if their $3000 Garmin com decides to fail while your custom cable just happens to be in use? Plus a $39 cable is an instant success too without running around 'building' something new.

If you guys want to read details about our cables, both are here if interested:

CRAZEDpilot GoPro/ContourHD/Camera Recording Cable

CRAZEDpilot iPhone Audio Recording Cable

Safe flying and audio!

~Brendan

 

[denverpilot]

Let me start by saying I'd happily use one of your cables if I needed one, but mostly out of laziness not some of the stuff below...

1. This is a matter of personal taste, but if you wish to use your audio for anything semi-quality, a good manufactured cable with a proper circuit design and shielded wire in an electronically noisy invironment (RF) will yield the BEST results. Fred, a recent customer, just sent us an email claiming it's a "..much better sound clarity than my cobbled-together Radio Shack solution". When impedance is properly matched the levels
in the audio are near perfect, without being distored from overdrive.

And why would I care what Fred says? What are his audio engineering qualifications? Haha. Marketing is fun.

Impedance can be matched a whole bunch of ways. A "circuit board" probably isn't necessary unless you're snagging the DC-bias and driving an OP amp. That's a $1.00 in low volume parts, about $0.18 high volume. Makes it easier to manufacture with a surface mount OP amp these days, I suppose.

There's a number of passive ways to do it, but levels can be low or high. High is easy to fix with resistance, low... back to the OP amp.

Impedance matching audio sources isn't hard, but it does require basic AC electronics understanding.

Shielded cable... Useful in some applications, totally dumb in others... depends on what noise you're trying to remove. Without a bypass capacitor of correct value, doesn't work at all for induced RF noise, for example... Just makes a better "antenna" for the big pop/click at each key up of a nearby transmitter.

2. Stabbing custom cabling into a $3000 com system in a rental plane (or any plane) is not worth the risk of damage if you ask me. Using factory soldered and tested cables is much safer - that's why I use one of our own cables for audio recording.

Heh. Yes if it's made by an idiot. Of course, the jacks utilized are more important than anything given the circuit isn't a dead short.

Factory soldering... Snort... I've seen some of that which would turn someone's stomach if they only knew. Had to reflow some factory solder joints over the years, too.

Factory TESTING is far more useful... Sometimes one simply doesn't want to take the time and discipline to design, construct, and TEST a cable or cable harness. Or uses simple continuity testers only that don't measure crosstalk in the cable, etc.

Hell, airline manufacturers can't even keep their 400 Hz hum out of at least one in ten of their aircraft's transmitted signals, judging by what I hear on the scanner and LiveATC. It's impressive how many jet radio systems are buzzing away with that.

I really think the risk point is the biggest point that hasn't been covered here. I'm sure it's debatable, but the fact is no one is as good at custom wiring a cable as a manufacturing team - what would you tell your FBO (or your wife) is you blow up a $3000 Garmin stack because of a stray ground wire??? Plus a $39 cable is an instant success too without running around 'building' something new.

The latter being a bigger problem than the former.

Unless I'm mistaken, Garmin has short protection on their audio outputs... Jacks make and break all sorts of inappropriate connections when sliding in and out.

The latter, however... Is a good reason to save yourself some time.

Hopefully since we are members here on the forum you'll cinsider our cables instead of the other links above. If you guys want to read about our cables, both are here:

CRAZEDpilot GoPro/ContourHD/Camera Recording Cable

CRAZEDpilot iPhone Audio Recording Cable

Safe flying and audio!

~Brendan

I definitely would, but not for the "audio cables are black magic, there be dragons here!" high pressure marketing talk.

I bet you can dead short any modern audio panel or radio's mic input with DC bias to ground, with no ill effects, and you certainly can short across the headset output, even turned all the way up to the audio amp limiter with a signal present, and not a damn thing will happen...

But I'll admit, since the manufacturers no longer provide schematics, I wouldn't forcibly try it.

It's a reasonable price for a reasonable product.

Don't go crazy over-selling it on some of the merits above. Start making claims it'll "never blow up an audio system in a rental" and a better idiot will be along shortly (pun intended) who's done something so screwy to their audio panel install that they'll sue your pants off when their direct line to the battery to give your gadget "more juice" is connected to the mic input. Haha.

Better to just say it works well, matches impedance, and wasn't assembled on a kitchen table...

Not to mention,,plenty of homebuilts with great audio panels, done right... made of kitchen tables...

"We've done all the work for you," probably suffices.

 

[CRAZEDpilot]

Thanks for the follow up Nate glad to see you here as well - yes it's not rocket science and many pilots are quite the builders and engineers but the original poster did not understand why it took $39 to make a cable when they incorrectly understood a straight wire with connectors would do the trick. That's the beauty of asking questions and learning.

Your followup with details supports it further; you have experience or knowledge in electronics and you didn't need the explanation Likely, you'd build your own cable, but most people don't, or find them selves experimenting with rather expensive radios until it works, which I wouldn't recommend typically without a high level of knowledge. You mention circuit boards, ours actually does implement a small PC board for the level matching circuit within a sealed and strain-relief housing to protect the components from the environment and to prevent wear or shorting from aircraft vibration environments.

It all woks out in the end - I could build my own plane too but I choose not to as I'd rather build electronics Then again, I'd rather just fly and do none of the above if I didn't have to earn a living! :wink2:

~Brendan

 

[thegazelle]

This should do the job

 

[CRAZEDpilot]

The 'mic-in-the-earpiece' trick is lack-luster at best. It's highly variable and unreliable. The levels are never the same from one flight to the next as it will varry based on position in the ear. If you want a quality and reliable audio recording, don't go that route just for the $20 you save. "Make a memory" and record something worth listening to!

 

[cocolos]

I was told this was a viable option:
"First: Split the connector with this: http://www.monoprice.com/products/p...=10429&cs_id=1042907&p_id=7221&seq=1&format=2
Then, convert one of the 6.53mm jacks to 3.5mm with this: http://www.monoprice.com/products/p...=10429&cs_id=1042903&p_id=7139&seq=1&format=2

Then, from the 3.5mm jack to the recorder, your favorite selection from here:
http://www.monoprice.com/products/subdepartment.asp?c_id=102&cp_id=10218

While the $45 connector is prettier, this should get the job done just as well. "

 

[CRAZEDpilot]

That simply won't get the job done at all I'm sorry to say - many people look at this as an 'adapter' problem but it's not - it's a SIGNAL problem. The MIC input on cameras/audio recorders or even your iPhone mic INPUT is at a different impedance and the audio out of the aircraft must be electronically altered with an inline circuit to match the expected input of the recording device. This is why the cable is $44 instead of $15.

Therefor, cable adapters simply don't cut it - not saying this cause we happen to sell the proper cable, I'm simply here to help educate that you don't want to spend your money in the wrong direction, and to help fellow pilots be successful in recording quality, usable film, ATC, or training audio.

We keep hoping to squash this misinformation that's been spread around that a few adapters will meet the needs. While you might 'hear' hummy overdriven garble with that solution, pilots deserve inteligable audio quality, considering we all spend well over $100/hr in most cases to fly we should record audio that we can understand later.

~Brendan

 

[flyingcheesehead]

The 'mic-in-the-earpiece' trick is lack-luster at best. It's highly variable and unreliable. The levels are never the same from one flight to the next as it will varry based on position in the ear. If you want a quality and reliable audio recording, don't go that route just for the $20 you save. "Make a memory" and record something worth listening to!

I've never had the variability problems you describe using that method.

In addition, many of us believe that audio that has the "color" of the slight bit of engine noise and wind noise that your headset doesn't eliminate is much more "worth listening to" than sterile audio panel output.