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This question is to help the "hard of hearing community" so that they can READ the phone/mobile call because they can not hear it.

Android has some really good (and free, too) apps which can convert voice to text with high accuracy and in many languages (Google Live Transcribe, SpeechNote etc.) Unfortunately as of now there is no feature to transcribe a phone call on Android (Google is working on it but it has a lot of complexities ranging from technical to privacy.)

To transcribe phone calls, I need help from experts.

A hard of hearing person will get call on his mobile phone. (Let us call this mobile "Mobile1.") A mobile headset will be connected to Mobile1 which will have left and right audio and a microphone.

Something like this:

enter image description here

How can I remove Output2 and feed this output to another Android mobile (Mobile2) microphone as input so that Mobile2 can transcribe the caller's voice successfully? A picture of that case is given below where Google Live Transcribe on Mobile2 is translating the voice (which it gets it from its microphone) to text.

enter image description here

I read on the internet and learned some basic terminology about the headset, so based on my limited knowledge, please guide me on how to connect the left or right audio channel wire from one headset to the microphone of another mobile.

Can you please give me a YouTube video demonstrating the making of that adapter or cable or some photos of how to make it so that I can connect with some local shopkeeper for the same because I am not an electronics engineer. I just want to help the deaf community around me and want to see happiness on their faces.


The answer to an old question gave me that idea that we can achieve what I was thinking but that I think the answer is not complete.


If I did not explain myself clearly please ask so that I can do my best to clear it. Please help to support the noble cause of making someone happy.


Edit 1 - Adding a rough diagram as per the suggestion by David.

@David - Can you please confirm whether my understanding is correct about the connectivity of different adapters from source to target mobile? If anything needs to be changed please let me know.

enter image description here

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  • \$\begingroup\$ Why do you think that the linked answer is not complete ? \$\endgroup\$ – AJN Apr 17 at 12:41
  • \$\begingroup\$ As I said I am not expert on circuit, and linked answer is related to line out. Maybe I am too much novice user for you but if you can please help to get the answer, I am doing this for a noble cause. \$\endgroup\$ – Dheeraj Chauhan Apr 17 at 12:47
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    \$\begingroup\$ @DheerajChauhan: I've started work on an adapter for your use. I'm putting the notes to it up on my blog. I want to work out a simple, robust setup that you can have made. That's going to take a little doing. \$\endgroup\$ – JRE Apr 29 at 20:58
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    \$\begingroup\$ @DheerajChauhan: I have posted an improved circuit on my blog. \$\endgroup\$ – JRE May 4 at 23:32
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    \$\begingroup\$ @DheerajChauhan: I'm getting the notifications. I'm writing a post which will include a parts list. 4.7 microfarads is a standard value and should be available anywhere. \$\endgroup\$ – JRE May 9 at 7:40
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I have had a look at the Google headset specifications.

You will not be making a transcription adapter using a pile of standard Y-cables and other adapters. That will not work.

The Android microphone input requires a certain resistance between the microphone and ground pins so that the phone can recognize the connected microphone. Simply cobbling a bunch of plugs and cables together won't make an adapter that the phone will recognize as an external microphone.

You will have to make an adapter that the transcribing phone will recognize as an external microphone, and that reduces the electrical level of the earphone outputs to something that is appropriate for the microphone input.

Google recommends this adapter for loopback testing of Android audio circuits.

enter image description here

Instead of connecting the headphone input of one phone into its own microphone input, we can modify that circuit to connect the headphone output of one phone to the microphone input of a second phone.

Like this:

enter image description here

You will notice that I changed the value of the capacitor. I made some measurements, and found that the circuit Google recommends attenuates the lower frequencies:

enter image description here

The red (earphone output) and blue (microphone input) lines should have the same shape, but with the blue line 20 dB below the red one. The 100nF capacitor that Google specifies does terrible things to the frequency response.

The 4.7µF part in my diagram has a frequency response that looks like this:

enter image description here

You could build the circuit I've drawn with a 4 pole CTIA plug at both ends, then use a 4 pole Y-adapter to plug it and a headset into the phone you use for making the call. The other end of the adapter goes to the transcription phone.

That would work, but it would be easy to plug in backwards - that wouldn't break anything, but it would be a nuisance to get properly plugged in.

Alternatively, you can build an adapter that plugs into both phones with a socket for the headset.

Finally, you can do what I did to try things out and build a headset with a transcription output.

This is the gadget I built to test the circuit:

enter image description here

I butchered two headsets and combined them into one unit to be certain that things will work properly before suggesting that you use my circuit.

It does work:

enter image description here

The same adapter could be used to transcribe phone calls or other audio from a laptop or PC - provided the laptop or PC has a 4 pole CTIA socket for the headset. Many of them do, these days. The signal levels should be close enough for it to work properly. I have not tested it, but it should work.

It would also be possible to make an adapter that would do transcriptions from the older, separate microphone/earphone plugs that many PCs have.


The same circuit could be used with a 3 pole socket to provide a line-in input to an Android phone for recording audio from other devices. It will mix a stereo input to mono, and attenuate it to an appropriate level for the phone's microphone input.

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  • \$\begingroup\$ Thank you very much again for all the time spent and I am really sorry for the late response as I was busy in work. I really appreciate that. Lockdown is still going on my side so everything is on hold my side. I will definitely give it a try. Would you like to please provide just a diagram of optimized loopback adapter so that the adapter can be used to transcribe audio/video using single phone itself ? Although you mentioned google loopback adapter but I think that also not optimized. \$\endgroup\$ – Dheeraj Chauhan 17 hours ago
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The easiest way to to it would be using a trrs y cable (1 male TRRS to two female TRRS) then one of the frmale TRRS could attached to a headset, then a TRRS to headphone breakout cables and attach to the other phone.

so One of these trrs male to dual trrs female:

MUY1MFFS

Source: https://www.startech.com/en-gb/cables/muy1mffs

Plug one into the existing headphones, the other into a headphone /mic break out cable:

MUYHSMFF

Source: https://www.startech.com/en-gb/cables/muyhsmff

Then plug another breakout cable in your other smartphone. install a mono to stereo 3.5mm on the mic side+smartphone unit :

PSG08563

Source: https://cpc.farnell.com/CN21107

Then link the headphone out put on the source to the mic input that has the adapter with a cable: MU15MMS

Source: https://www.startech.com/en-gb/cables/mu15mms

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  • \$\begingroup\$ Granted, if you have the solder skills you could build your own, but if a customer came into my store I would just sell them that solution. \$\endgroup\$ – David Mikeska Apr 17 at 17:00
  • \$\begingroup\$ Dear David sir- Thank you very much for your time which you spent on writing the answer. I will go through all the adaptors which you mentioned and will try to understand as well will try to find out all these adapters in local market. Blessings of Deaf community will be with you. It is possible for you to share link of this adapters online (Possibly on Amazon) ? I am new to this platform - Is there anyway to connect one to one sir? Thanks again sir. \$\endgroup\$ – Dheeraj Chauhan Apr 17 at 17:48
  • \$\begingroup\$ This approach doesn't account for the fact that microphone inputs and headphone outputs operate at significantly different amplitude levels. \$\endgroup\$ – pericynthion Apr 17 at 18:04
  • \$\begingroup\$ Dear Peri - Can you please suggest what else can be done? Although today a local shopkeeper tried to connect output2 of headeset (refer picture 1 in my post and ) to input of mic but it did not work. So somewhere that amplitude level must also have some role which needs to be taken care although i dont understand that term. Your input please. Please help to spread the smile on the face of needy. \$\endgroup\$ – Dheeraj Chauhan Apr 17 at 18:10
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    \$\begingroup\$ mileage varies when interconnecting devices. @pericynthion But most phones have a way to attenuate the mic signal. Cheers! \$\endgroup\$ – David Mikeska Apr 17 at 18:19

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