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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

JRE
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Dheeraj Chauhan
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  • Why do you think that the linked answer is not complete ? – AJN Apr 17 '21 at 12:41
  • 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. – Dheeraj Chauhan Apr 17 '21 at 12:47
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    @DheerajChauhan: I've started work on an adapter for your use. [I'm putting the notes to it up on my blog.](https://josepheoff.github.io/posts/androidtranscribe-toc) I want to work out a simple, robust setup that you can have made. That's going to take a little doing. – JRE Apr 29 '21 at 20:58
  • @JRE - "@JRE" - I have gone through the blog, Fantastic ! You have articulated it very well and definitely you are thinking 360 degree (volume control button etc.) Now I am sure something "Perfect" is in the way and very soon adapter will be available. – Dheeraj Chauhan Apr 30 '21 at 05:59
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    @DheerajChauhan: I have posted an [improved circuit](https://josepheoff.github.io/posts/androidtranscribe3) on my blog. – JRE May 04 '21 at 23:32
  • @JRE - loved the name you have given to adapter i.e. "Transcription Adapter", just awesome! Thank you very much for putting effort/time/energy to help the needy community. Now I understands it was not trivial task although it looks trivial from quick theory. There was a lot of explanation in the improved circuit but my take away was modification in C1 :) I have one question- can you please tell me what all components (resistors,capacitors,shields you mentioned to avoid noise ? etc.) I should have which maybe needed in future so that there will be no need to go city again and again. – Dheeraj Chauhan May 05 '21 at 05:07
  • As of now I can see the below list which I should have with some redundancy- 6 1K resistors, 6 2K resistors, 6 5K resistors, 6 10K resistors, 6 100ohm resistors, 6 500ohm resistors, 3 100nF(non-polarized) capacitors, 3 330nF(non-polarized) capacitors , 3 4.7µF(polarized) capacitors , what shall I ask to shopkeeper for shielded cable? I am afraid whether the capacitor with fractional value( I means 4.7µF not 4µF,330nF not 300nF etc. will be available? or it is kind of some customization?). Please add more, most probably I missed many. – Dheeraj Chauhan May 05 '21 at 05:08
  • @JRE - Did not hear from you since 2 days or maybe you missed my comment, I hope everything is good? Maybe you are too busy on making the adapter in the best way now ( shielding and some other things you were mentioning) for the prime time show :) I am also much excited but as lockdown is going on so can not do anything, so as of now your blog is the only thing which is making me happy. Keep posting and keep rocking ! Hope to hear from you today. – Dheeraj Chauhan May 07 '21 at 05:36
  • @JRE - just checking whether you are getting comment notification your side. – Dheeraj Chauhan May 09 '21 at 02:00
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    @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. – JRE May 09 '21 at 07:40
  • @JRE - Thanks. I am curious about 2 more additional points- 1) What is efficiency of this adater in case we want to use tue same in laptop to transcribed skype/Microsoft Teams/Zoom/google meeting etc call or some tweaks are required to make it more efficient in case of laptop? 2) The same adapter can also be used with little modification to transcribe the podcast/video/whatsapp recording etc so that second phone is not needed at all i.e. output of phone will be input to its mic itself. Sorry if I am deviating from the main topic but I strongly believe that both will make life easier for us. – Dheeraj Chauhan May 09 '21 at 09:47
  • In case you can shed some lights or can express your opinion about above 2 points it will be great. You have very good knowledge so in case you can guide on the same too that will be bonus, if required I can ask another question about the same so that things will nox mix up. I am.sure many hearing impairment people are morr dependent on computer than phone and some of them would like to listen postcad/videos/offline recordings etc to catch-up things. I apologized in case I am offending you with my junk requirements, if so please ignore and dont reply back, you are already on this noble cause. – Dheeraj Chauhan May 09 '21 at 09:54
  • @DheerajChauhan: I've put my results into an answer to your question. I've also posted a [complete guide to building an adapter on my blog.](https://josepheoff.github.io/posts/androidtranscribe4) I'm not done, but it will be a few days before I can do more. I have parts ordered, and I can't do much until I get them. – JRE May 10 '21 at 20:42
  • It would be possible to make a "loopback" adapter to transcribe podcasts, audio books, or videos using one phone. [Google's "loopback" adapter](https://source.android.com/devices/audio/latency/loopback) is where I started from. – JRE May 10 '21 at 20:44

2 Answers2

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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.

JRE
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  • 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. – Dheeraj Chauhan May 17 '21 at 04:56
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    @DheerajChauhan: I've described and tested a [loop-back adapter](https://josepheoff.github.io/posts/androidtranscribe5) on my blog. – JRE May 18 '21 at 14:24
  • look fantastic ! As always very detailed explanation ! So many things to try out once lockdown is finished , but well it seems will go for some more times , maybe for next 15 days ! Till then I can enjoy reading your blogs and knowledge. Please post something else also which may be helpful for community which maybe I am not thinking. Electronics can help us in many ways ( I am sure Google will take hell lot of time to make that solution working using software ) very quickly and that's the power of hardware and sharp knowledge like you have ! – Dheeraj Chauhan May 19 '21 at 05:33
  • Current "Transcription adapter" is good enough to transcribe the phone call in second phone. But user will required an additional adapter to connect "Transcription adapter" as well as "Mic/headset" to phone1 so that user can speak on phone1 to caller. So my question is-Can we enhance the design of our "Transcription adapter" so that a mic will be attached to it itself and thus no further overhead of additional trrs male to dual trrs female adapter/headset is needed and our current adapter will be a complete package ! Just a thought from my side in case you consider it is feasible? – Dheeraj Chauhan May 21 '21 at 04:56
  • @DheerajChauhan: [The adapter I described in this post](https://josepheoff.github.io/posts/androidtranscribe4) is complete. It is a normal headset that you can make phone calls with. The microphone and earphones on the headset work normally. I built it to be used that way, and tested mine to be sure the headset works like a normal headset. The second plug goes to a second phone to do the transcription. That second plug only has the voice of the other person on it. – JRE May 21 '21 at 08:29
  • The two plugs have different functions. You must plug them into the correct phone for it to work correctly. That's why I made mine with two different colored plugs. The white plug in my adapter goes to the call phone - it is connected to the headset. The black plug goes to the transcribe phone. – JRE May 21 '21 at 08:31
  • If the headset doesn't work, swap the plugs and try again. If that still doesn't work there was a mistake made in the wiring. – JRE May 21 '21 at 08:32
  • My bad ! Effect of lockdown ! Everything was a complete package and I did not notice that ! Thanks for pointing out my mistake. It seems a complete package and very efficient too. Once lockdown is removed I will try it. Thanks again ! Happy weekend ! – Dheeraj Chauhan May 21 '21 at 13:02
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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

David Mikeska
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  • 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. – David Mikeska Apr 17 '21 at 17:00
  • 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. – Dheeraj Chauhan Apr 17 '21 at 17:48
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    This approach doesn't account for the fact that microphone inputs and headphone outputs operate at significantly different amplitude levels. – pericynthion Apr 17 '21 at 18:04
  • 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. – Dheeraj Chauhan Apr 17 '21 at 18:10
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    mileage varies when interconnecting devices. @pericynthion But most phones have a way to attenuate the mic signal. Cheers! – David Mikeska Apr 17 '21 at 18:19
  • @David sir, so that means it should work and amplitude factor can be ignored? – Dheeraj Chauhan Apr 17 '21 at 18:23
  • @DavidMikeska I have added the diagram of connectivity of different adapters suggested by you. 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 do let me know. – Dheeraj Chauhan Apr 18 '21 at 07:10
  • Also can you please tell me why we needed Male to female TRSS adapter and Mono to stereo adapter? It seems setup should work without them. – Dheeraj Chauhan Apr 18 '21 at 09:21
  • @pericynthion - Can you please help ? – Dheeraj Chauhan Apr 19 '21 at 05:09