Feeding External Audio Into Android Cell Phone

It seems like smartphones will do anything.  But do they make effective sound recorders?  That depends on what you are looking (listening) for and what type of phone you have.  Below I describe ways to record on your smartphone, with examples of products that might help.  Most of this discussion is about Android phones and iPhones; tablets are for another day.

There are 4 basic ways to use your phone as a recorder:

1. The built-in microphone(s).
2. Using a microphone plugged in through the headset port.
3. Using a microphone plugged in through the charging port.
4. Via Bluetooth.

The built-in microphone

If you are looking to use your phone as a voice recorder, for recording personal notes, meetings, or impromptu sounds around you, then all you need is a recording app.  I would highly recommend getting a third-party app, as the apps that come with the phone are pretty basic.  Important things to look for in an app are the ability to: 1) adjust gain levels; 2) change sampling rates; 3) display the recording levels on the screen, so you can make any adjustments necessary; and, perhaps not as important, 4) save the files to multiple formats (at least .wav and .mp3).  Also very handy is the ability to email the recording, or save it to cloud storage, such as Dropbox.

Microphones on various models of phones vary quite a bit.   Newer phones have two or three microphones, but differ quite a bit in their sound recording abilities.  Especially problematic seems to be recording loud sounds, such as concerts, although even those capabilities are improving.

External microphone through the headset port

Most iPhones and smart phones these days come with a TRRS port for the headphones.  If your headphone jack has 3 lines (4 rings) on it, it's a TRRS, which means it can act as a microphone as well as headphones.   Before you attempt to connect an external microphone via the headset port, make sure it is a TRRS port.

Note the 3 (white) lines in the plug for the ear buds from my Samsung Galaxy S3, compared with the 2 (black) lines in the plug for a lavalier microphone.  The color is irrelevant, but the number of lines is not.

Because of the differences in jacks, you cannot plug in any old microphone with a 3.5mm plug and expect it to work.  Luckily, several manufacturers have developed microphones that plug right into the headphone jack.

Note that this does not appear to work on all devices and microphones, apparently there are some differences in impedance levels of the microphones that the phones can't deal with.   [GEEK NOTE:  TRRS jacks typically supply 1.5-2.5v, with 1.0-1.6KΩ impedance, which varies by phone model and manufacturer.]  Some adapters are for microphones with batteries, and others specify microphones with no batteries.  Some of these connectors also allow simultaneous monitoring if you plug ear buds or headphones into the other jack.  This is very helpful in making sure you are recording what you want, otherwise you need to watch the visual input displays (if your app has them) or wait to play back the sounds.  Even if you get the proper adapter, the microphone may not work properly with it.

Note that the power to these microphones is pretty low, so they are probably not capable of recording quiet or distant sounds without adding a lot of microphone noise.  The TRRS port allows only one microphone input, so the signal will be mono no matter what type of microphone is used.  Some apps split the signal into two mono signals, but it will not be true stereo. It is not possible to get a stereo input through the TRRS port. Some companies are selling fancy-looking setups with two mics that are supposed to be stereo, but there is only one input in the jack, so it is still a mono signal.  They appear to function quite well in office and studio settings, but are probably not suitable for nature recording.  A pre-amp, such as the Tascam iX2 would help, but is only for XLR mics.  I would love to hear about any experiences using smartphones with external microphones.

Recording through the charging ports

There are fundamental differences between Apple and Android in how they handle recording through the charging ports.  Basically, iOS includes audio support; Android does not.  Google farmed audio support out to the device manufacturers, resulting in much confusion about which devices are compatible and which are not.

External microphone plugged into the micro-USB port for Android

Some smartphones, including my Samsung Galaxy S3, LG G4, and Moto G5S+come with a USB host, which means the mini-USB port (charging port) is capable of sending power.  To check if your phone has a USB-host, either Google "USB host" and your phone make and model.  You can also search "USB host" and it will list current phones with USB Hosting ability. There are also several apps in the play store that can check if your phone has a USB host (search for USB OTG).  If you phone has a USB host, you can use a USB OTG adapter to plug in a USB mic (you must have the correct adapter).  Again, this is low power, but is quite suitable for recording podcasts or narration overlays for video.

Below are some examples of USB microphones that reportedly work well:

It is also possible to plug in a USB audio interface, which greatly increases the options for adding multiple microphones, instruments, and MIDI devices.  However, not all devices will support USB audio.  According to the developers of Audio Evolution:

"Some Android devices have USB host but lack certain kernel features that are needed for USB audio.  These are usually cheap 'Chinese' tablets, but also the Samsung Note 1 and Galaxy S2 lack it.  When your device has a Rockchip cpu inside, chances are very high it will not work."

In addition, some USB microphones and audio interfaces need more power than the phone can supply, and so may need a powered USB hub to function properly.

It is possible to plug a microphone with a 3.5 mm jack into the USB port, using something like an iMic 3.5 to USB adapter, or USB mixer with 3.5 mm mic inputs.  I have tried this with a couple of different lavaliers, one powered, one not (mic to iMic to USB-OTG to phone).  The signal was a little noisier than my dedicated recorder, but comparable to the TRRS port of the iPhone and much better than the Samsung's TRRS port.

It is also possible to plug a professional mic into a smart phone, using something like the Blue Icicle (these convert an XLR to USB and provide phantom power).  Some also include gain controls so you can control the level of the recording.  I have not tried these setups, but there is information on the web about them.  They primarily seem to be used for podcasts and studio work.

Note that for the adapters shown above, you are going from mic to usb adapter to USB-OTG to phone.  That creates several potentially weak links in the chain and more places for problems.

Using the lightning port of iPhones

Several manufacturers have developed microphones that plug into the power port of iPhones and iPads.  If you want to record in stereo, this seems to be your best option.  These microphones have helped turn iPads into miniature sound studios.  Because different Apple devices have different configurations for their charging ports, make sure the mics are compatible with your device, although adapters may be available.

There are also converters available to allow 30-pin and lightning ports to accept USB devices, including microphones, mixes, preamps, MIDI devices, etc.

Recording via Bluetooth

Because most iPhones and Android devices are equipped with Bluetooth, which allows wireless connection between devices, they can receive signals from Bluetooth microphones.  For this, you need a microphone capable of transmitting a Bluetooth signal and an app capable of receiving the signal.  Most applications of this technology have been focused on the video industry, with most Bluetooth mics being lavaliers that allow wireless transmission of dialogue.

Examples of Bluetooth microphones that couple with iPhones and Android devices:

There appear to be a lot of problems with Bluetooth microphones connecting with smart phones, in terms of microphone and signal quality.  It may be a little early for this technology yet.

Tips for recording with your smart phone

1. Recording via USB is a better option than TRRS is your phone supports it.
2. If you are connecting an external microphone, make sure the connectors are compatible with your phone.
3. Watch your sound levels to make sure you are picking up enough sound, but not overwhelming the microphones.
4. Simultaneously monitoring the recording helps get the recording levels within range.
5. Getting close to the subject picks up the sound you want and minimizes background noise.
6. Avoid windy situations and/or protect the microphones.
7. Sound files can be large, depending upon your sampling rate, so make sure you have enough storage space.
8. If sound recording is going to be an important use of your phone, consider an iPhone over an Android or Windows phone.

Smartphone or Dedicated Recorder?

Although smartphones are very convenient, for field recordists they are not a replacement for a dedicated recorder.  Dedicated recorders allow adjustment of gain and the ability to apply filters, and have more powerful pre-amps.  They have more settings for recording, including setting the sampling and bit rate.  And for nature recording, where you may want to set up your recorder and leave it record for a while – who wants to do that with their phone?

But if you use your phone for shooting video or for recording conversations, an external mic will be a great improvement over the on-board mics.  For podcasting or recording quick conversations, a small microphone added to a smartphone would be convenient and adequate.  Some of the microphones made for use with iPhones and via USB host are capable of recording in stereo; overall, iOS seems way ahead of Android when it comes to sound recording.

With the rapid gains in technology in smartphones, they may overtake recording they way they have overtaken photography.  Now if they could just improve the quality of the sound in a phone call….

Last modified September 20, 2021.

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