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So far, I thought it was a firmware error, but now I just found a 2nd device that has two internal microphone capsules but only yields a monophonic signal (1st one was the S2 Plus GT-I9105P with Android 4.1.2 and now the HTC One M7; the Nexus 10 with Android 4.4.2 has only one mic).

I tested with:

bufSize = AudioRecord.getMinBufferSize(44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT);
ar = new AudioRecord(source, 44100, AudioFormat.CHANNEL_IN_STEREO, AudioFormat.ENCODING_PCM_16BIT, bufSize);

and set source according to How avoid automatic gain control with AudioRecord?

I also tested some apps if they were able to produce real stereo recordings but did find none (I tested the standard Camera/Camcorder, Audiorecorder, and RecForge Lite).

So my question is: How to enable stereo recording on tablets/smartphones yielding only mono albeit having two internal microphones?

Add on question if there is no way to achieve real stereo recordings: Could you name other devices with also two internal microphones but only mono recording capability?

Is there any API or trick to find out programmatically?

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Hartmut Pfitzinger
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  • I don't know the answer to your question, but I thought you might want to consider either using the audio headphone jack to plug in a stereo microphone, or using bluetooth 3.0/4.0 to use a bluetooth microphone. http://android.stackexchange.com/questions/19368/how-do-i-use-an-external-microphone-with-my-galaxy-nexus If you really want to get creative, you could even try using a micro-usb to usb on-the-go (OTG cable), or try using two different android devices recording at the same time and later recombining the two channels. – Stephan Branczyk Feb 16 '14 at 13:00
  • The audio jack is only for [mono mics](http://stackoverflow.com/questions/14812579/line-stereo-2-channel-recording/15115249#15115249). Anyway, I was interested in doing stereo recording via the built-in mics. – Hartmut Pfitzinger Feb 16 '14 at 13:20
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    The primary use for multiple mics on mobile phones is to get improved noise suppression. Some vendors also add support for stereo recording since they have the necessary hardware anyway, but there's no guarantee that a device supports stereo recording just because it has 2 (or more) mics. Also, keep in mind that there will be very little difference between the left and right channels since the mics often are very close together. As far as tricks go, there are none that I know of. On the devices I've worked on that supported stereo recording it was just a matter of requesting 2 channels. – Michael Feb 16 '14 at 14:53
  • Hartmut, You're totally right. I had not read the actual customer reviews on those Android/iPhone mics claiming to be stereo. http://www.amazon.com/Opteka-VM-1000-Calibrated-Directional-Microphone/dp/B006BF0N6O/ That being said, if you have products like Square, https://squareup.com/ capable of using the analog input jack in undocumented ways, it should be possible to cram a stereo sound through a mono channel, and then take it back out again. This is essentially how 3D phones with 2 back cameras cram stereo images into existing 2D formats (at the cost of losing half the information density). – Stephan Branczyk Feb 16 '14 at 18:14
  • On a side-note, there is a company in San Francisco that makes Android piano devices that were showcased at Google IO two or three years ago. Those specialty devices may have what you want. If you're interested, I should be able to find the name of that company, I have their business card somewhere. – Stephan Branczyk Feb 16 '14 at 18:21
  • Actually, I try to make available stereo recording via the internal microphones with as many different devices as possible. Special solutions are interesting but not what I am looking for, here. Actually, I just recall that the HTC ONE is also a candidate! – Hartmut Pfitzinger Feb 16 '14 at 18:24

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See what worked for me in the Motorola Moto G. I understand it is very dependent on the vendor/model, but I tried many combinations until I found that only with 48000 Hz I was getting stereo recording in that particular phone:

Recording stereo audio with a Motorola Moto G (or Moto X)

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jimijazz
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