Recording Aircraft Intercom
 

I know its been discussed quite a bit but there's nothing that specifically answers my questions. I have a sony px 470 voice recorder which i am planning to plug into the spare output on the passenger seat in order to record intercom audio in a PA28. Previously, i have tried the sony px240 and initially i thought it would be fine because i ran a test recording pre-flight and it sounded okay apart from a slight whining in the background. After my flight i listened back to the recording and from when the engine had started the whining was very loud and increased in pitch as RPM increased and voice was slightly overdriven. After a bit of research i have found out that overdriven audio is because i was using mic-in instead of line in/ audio in, but nothing to explain the whining (my guess is alternator or something). Since then, i have now purchased the px 470 because it has an option in the settings to change external devices to audio in instead of mic in. Here are my questions:

Is 'line in' and 'audio in' the same?

Would the whining effect be eliminated with Audio/line in input?

Has anybody had any experience with this?

I am aware that you can place a small mic inside the headset (which will be my next option if this fails), but i would prefer to have something out of the way. Also, i am aware that there are certain laws regarding ATC transmissions etc, this is purely for personal use so don't worry!

I know its a bit of a techy question so i appreciate any advice or knowledge!

Thanks
Matt

I use a splitter cable from Nflightcam.com in combination with a gopro. Good audio quality and it blocks out the engine/prop noise because your headset will take care of it.

I made up a splitter lead and put a 10k and a 1k resistors as a 'Tee', then a 3.5mm plug. This reduces the audio down nicely for a 'mic' in. Cost was less than a fiver. I use a £17 action camera from a well-known auction web site. I removed the built-in mic from the PCB and put a 3.5mm socket in the case with leads to the PCB mic input. Again, less than a fiver. The video quality is pretty poor but I use this soundtrack in conjunction with higher quality video from a GoPro when editing. The whole cost of the audio setup including the camera was less than the GoPro lead.

TOO

Was your wife on board?:ok:

I use a lapel mic (minus clip) inserted under my right ear cup. I have ANR headset, and the audio is fantastic quality without any fancy wiring.

We use this: https://www.telonics.com/products/ac...io-systems.php

I'm not connected to the company at all...

The usual 'In's' are different in electrical impedance. If you don't know what this is, you are kindly asked to get yourself educated. In such environments it is usually not advised to connect different electrical circuitry without exactly knowing of the impact of your actions! The way out is to either make yourself acquainted with the basic knowledge of electronics, or go the easy consumer way - buy an adapter which decouples the aircraft electrics from your electronics.The usual commercial adapters - due to liability - must have this feature. So, short, buy one of the cables with the boxy electronics in line to get rid of the coupling issues.

Oi, that's what I said! :)

Quite probably. Years ago there were standards for audio interconnections, but in the modern world they have all been lost long ago.
Mic in is usually a much higher sensitivity than "line-in" so will invariably be overdriven by too high a level of audio. Most modern recording devices have some sort of Automatic Level Control (ALC) to prevent overdriving the device.
The whine you are hearing is most probably alternator whine which is probably not very noticeable on aircraft headsets, but the recording device in the absense of any intercom audio may ramp up the gain and pick up the whine. My advice would be to connect your line in via a capacitor and small potentiometer, that way you can adjust the audio level for the best results and minimise the whine. A A2 uF capacitor onto the centre pin of an audio jack. Connect a 5 K potentiometer from the other end of the capacitor to ground. Take the audio from the slider (centre pin) of the pot to the recorder with the ground from the barrel of the jack. Adjust the pot for the best recording.

Or simply buy one of these: https://www.telonics.com/products/ac...io-systems.php

Thanks everyone, some very interesting ideas! I tested the recorder on another aircraft that my flying school uses and there was no whine whatsoever! I also took my gf up for a flight in the aircraft i was experiencing issues with and she plugged her headset into the same output(rear pax seat) and we could all hear the alternator whine through the headset (this is was with no recording gear), so it must be an issue with the intercom in the back!

sounds nice and cheap, i like cheap! thanks!

She was on the second flight, it was more noticeable ! ;)

Do you get any issues with the rustling of the cable moving about though or you touching your headset?

Definitely something i would like to invest in the future when im more serious about filming, thanks!

If you have dynamic headphones I used an old telephone pick which had a small suction cup to stick it on. This is basically a coil of wire which couples via the variation in the magnetic field. Records anything you hear and picks up no back ground noise.

May be find one on ebay or google telephone pick up.

I use a Garmin Virb Elite with a 3.5mm Splitter.
Pretty inexpensive used on the "Bay of Evil" ATM