I get the feeling is that to feed a line level signal to the 3.5mm hands free kit jack socket, one merely needs to
Capacitors should not make a difference if the source is AC coupled but it’s a good point – you might otherwise end up shorting the mike power, although that should be going in through a resistor anyway.
Looking at the PA80i that’s all it can be…
I have a Samsung Galaxy S3 and it works with that kind of setup, although it only has a mic input. (Well, at least it is called a mic input.)
The cable I use (a Pilot Communications PA80i) could have series capacitors which might make a difference.
I have now tested my adaptor and it works great. It is much better that sticking a small microphone up the headset because all sound which doesn’t break the squelch on the radio(s) is totally suppressed, so you get proper silent silences, with zero engine noise. Only when the squelch is broken do you hear engine noise, which is then dependent on how good the noise compensating headset mikes are.
It’s clear – for the devices I record with – that the potentiometer is needed because at least one of them doesn’t have enough leeway in its level control to accept the an-attenuated signal.
This is a quick and dirty video I did yesterday
There are devices which don’t have a variable attenuator so the pot is really needed. For example my Pentax K3 DSLR, under its external record menu, has a “volume control” adjustment but it doesn’t seem to do anything to the record level, and just to make it more interesting it clips horribly even for a sound level which doesn’t reach anywhere near the peak on its level meter…
What will be interesting is whether the Samsung S6 phone (which I am looking at getting) will work with it. I am very sure it won’t because it has a mike input only, not a line input. It may mean that the only way will be to cut the speakers off the hands-free kit and glue the mike switch in the ON position – that is what I did on the Nokia 808.
Your audio sounds superb – I think I’d go as far as saying it’s the best I’ve ever heard.
Great! I won’t change a thing!
I was surprised that the voltage coming out of the headset socket is probably not far off a line level (770mV rms across 600 ohms) which is why just a simple cable works OK.
If a camera has only a mike input, that’s going to be completely different especially if it is the “plug in power” electret mike sort of thing, which historically most camcorders had (all the Sony ones I had, for sure). Much more sensitive than line level. Plus you get the 4-pole jack plugs, etc.
And once it’s buggered, it cannot be recovered…
Chris, most cameras expect a microphone to be connected not a line level source. Your cable only works with your recorder because you were able to set it to expect a line-level input.
If you connect a line level source to a microphone input without attenuating it, it will sound awful (and look like Peter’s second screenshot above).
Your audio sounds superb – I think I’d go as far as saying it’s the best I’ve ever heard.
If it sounds good then it’s good 
You can see clipping in the sound track when you import the audio into your video editor.
This is non-clipped (except very brief spikes, which nobody will hear anyway)
This is well buggered and will sound horrible
It’s a bit like overexposing (washing out) parts of an image. Once the data is gone you will never get it back.
Cameras are probably more sensitive than a voice recorder so my cable is probably good enough?
I think just
I think just a cable will do the job for most people, I had no idea what sort of signal level is going to come out of those sockets, and with a camcorder which has a manual level control I don’t know what levels it can accept. And if you feed in too much, it will clip it and the whole sound track will be ruined. AGC is no good because it just winds up the gain during the periods where nobody is talking.
I should have experimented with turning the pot all the way up (i.e. simulating just your simple cable, Chris) and seeing how the manual level adjustment on the camera handles that, but I ran out of time.
Peter,
What are the advantages of your cable vs a simple plug and 3.5 mm <=>3.5 mm (that I use)?
