Topic: unique cabling situation (cell phone)

[Gizby]

I've had an idea for a video short. Basically, I want to have a camera focused on someone talking on a cell phone. The audio heard would be what she is saying into the cell phone, while the person on the other end is heard through a regular studio microphone. The idea is kind of a disconnect between who is seen/not seen and how they are heard.

To record this properly, I thought of cell phone headsets. As far as I can tell, they are little more than a signal going to the earpiece and a signal coming from the mouthpiece, in and out of the 2.5mm jack on the phone. My recording device is the FR2-LE. So here is the signal path I envision:

1) 2.5mm (out of cell phone) > FR2-LE XLR input (left channel) > WAV
2) microphone [ > SD MixPre] > FR2-LE XLR input (right channel) > WAV > RCA monitor out (right jack) > 2.5mm (in to cell phone)

So I'm basically recreating the experience of the headset, albeit with better equipment and a somewhat more convoluted path. The first step captures what the person on the other end of the phone is saying with that oh-so-familiar tinny phone quality we all know and love. The second step records someone talking into a microphone before pumping it back into the cell phone. The additional preamp step is put in there so I wouldn't have to enable phantom power on the FR2-LE. I think the effect, when synced up with video, could be interesting.

My problem is in designing the cabling to get this done. I'd need some sort of split cable. Coming out of the cell phone, it would be "2.5mm jack > XLR" (it could be a 1/4" TS phono plug, but I don't really want to deal with attenuation). Going back into the phone would be "RCA > 2.5mm jack". It's an odd looking cable setup, to be sure.

So I have a few questions. Can this (or a similar) setup work? I'm not knowledgeable about how cell phone technology works, so there very well may be parts in a headset that I couldn't recreate in this setup. If this can work, splendid. How hard would it be to put this together? I've had some experience with soldering and splicing, but not a whole lot. And short of buying a headset and cannibalizing it for parts, I'm not sure where I would get all the parts to put this thing together. Should I try having one of the cablers around here to put together this custom cable? And if so, just who has the parts to put together such a monstrosity?

I await your replies.

[marksk]

i have a sony ericsson 810i and you can record a call directly to a file on the phone. perhaps you can look for a phone with that feature.

[rastasean]

JK Audio makes a device that would work. Cell tap
http://jkaudio.com/celltap.htm

Coming out of it, I imagine you could do 1/8" to XLR to the fr2le.

If it does not HAVE to be a cell phone, the quick tap is less expensive of an option:
http://jkaudio.com/quicktap.htm

Keep me posted because I've been interested in recording phone conversations as well.

-Sean

[rastasean]

That seems to be a transformer tap off the speaker, but not the mic.  Their FAQ says:

I just purchased one of your Cell Taps and the headset jack doesn’t seem to work. The only thing we can record is the incoming audio, not our own. What can we do?
!
   

Unfortunately, we are seeing this more often with the newer generation of cell phones. Many of them do not provide sidetone, which is your own audio at the headset output jack. If your audio is not present at the headset jack, it cannot be recorded as there is no other way we can access the audio on a cell phone. You might try the Cell Tap with another cell phone to see if it will be compatible. To test the phone first, connect your headset to the phone and listen carefully to the headset while you speak into the mic. If you can hear your own voice in the headset then the phone should work with our Cell Tap.

Sure, there is a way they can access the mic audio, it's just a bit more involved.

First, my 300th post!! thank you to all you tapers!

That very interesting and I didn't think to check the FAQ.

Maybe it would be easier to have the cell phone dial a land line and record the audio from the phone call. Camera pointed at the person on the cell phone with the phone audio over dubbing it. may not be a bad solution.

[Gizby]

Assuming you have a cell phone that uses a 2.5 mm plug (most, but not all, do), you also need to supply bias voltage for the microphone.  That's probably 1.5V to 2.5V.  You can probably just leave the mic connected to the phone (for the bias), but tap the cable for both signals into a suitably high-impedance input (10K ohms or more).

Interesting. I figured this would be a bit more complicated than I figured. Something like that is beyond my unfortunately limited electrical skills.

i have a sony ericsson 810i and you can record a call directly to a file on the phone. perhaps you can look for a phone with that feature.

Not an option for me, though I didn't know phones were doing that these days. Good to know.

JK Audio makes a device that would work. Cell tap
http://jkaudio.com/celltap.htm

Coming out of it, I imagine you could do 1/8" to XLR to the fr2le.

If it does not HAVE to be a cell phone, the quick tap is less expensive of an option:
http://jkaudio.com/quicktap.htm

Keep me posted because I've been interested in recording phone conversations as well.

-Sean

Both items are a tad rich for my blood, but great suggestions. They also make me realize that I am being a narrowminded. I didn't even think of using a landline phone. That would probably be much less complicated to capture the audio coming out of it. And really, I don't need to feed external audio back into the phone; I can easily mic the person who is talking on the phone. That makes things a good deal simpler.


So yeah, I just have to figure out how to capture the audio coming out of a phone, be it cell or landline. That product would do the trick, but I'm going to see if there is anything cheaper. And of anyone else has any suggestions, I'd love to hear them. +Ts all around.

[Gizby]

Me again.

So I got my hands on a headset that I could tinker with. Cracked her open, pulled out the headphone bit, and I found the below picture. So it's just those two wires leading to the headphone with one wire (I think it's just one) from the microphone heading back to the 2.5mm jack. Seems to make sense. So I need to take the red and blue-green wires, splice them into a new cable, and send them on over to an XLR connector. (I'm not going to worry about rerouting the microphone signal, I'm just going to mic the person who is talking). I don't know how those two diodes there come into play, however. That might be what mshilarious was referring to in regards to bias and impedance (again, I apologize for my lack of knowledge in this field, I've only had a little experience in basic soldering).

Does anyone have any tips on how to properly and safely reroute the headphone signal so I can plug it into my recorder and capture it that way? Thanks.

[JackHenry]

Why not just record the person talking on the cell phone via a normal 'out of camera shot' microphone?