Add an audio input to Android

Add an audio input to Android


Android phones are great for recording through the internal
microphone, but what they lack is an external input you can plug
analogue audio sources into. That’s not strictly true because you
can add an external audio input to your phone for less than $10.
Here, we show you how to record audio directly from external
devices.

 

TRRS
Most Android smartphones are designed to allow you to make calls
using the bundled earphone set, through a small mic embedded in the
inline controls. If your phone has this ability, it’s because the
earphone socket is known as a TRRS type (Tip, Ring, Ring, Sleeve).
Basic stereo headphones only need three connection points – the
fourth point here provides the mic connection. It’s this fourth
connection we’re going to utilise.

First, you need to get a 3.5mm to three RCA socket adapter (Dick
Smith catalogue #P6575, $9.98). This adapter is normally used for
camcorders, but plugged into your phone’s headphone socket, the red
RCA socket becomes the external audio input. (The 3.5mm plug is a
TRRS type). You can then feed that RCA socket with any suitable
audio cable. For example, if you’re recording audio from a radio or
an iPod, you’ll need a 3.5mm to stereo RCA cable (Jaycar catalogue
#WA7014, $6.50). You just plug one of the RCA plugs into the red
RCA socket on the adapter, while the 3.5mm plug goes into the radio
earphone output.

 

Free Android apps
To check that you’ve got the cabling right and to record from the
external device, you need two apps: Audalyzer and PCM Recorder.
They’re both free from the Google Play Store (formerly Android
Market). Get those both into your phone and fire up Audalyzer.

The next bit is a little tricky. What we’re doing here is
turning your phone’s mic input into a line input; the problem with
that is a mic input is designed to work with a very tiny signal
level. Feed the output of your notebook’s sound card straight into
the mic input, for example, and you’ll completely swamp it. So, the
first thing is to drop the audio output level of your playback
device down to nothing. Plug in the cables, switch your phone to
Audalyzer and you should get an audio level reading of about -60dB
or so. This is what’s called the noise floor of your phone’s audio
input section.

Now, with music or whatever playing and starting with zero
volume, very slowly start increasing the device’s audio output
level notch by notch. If everything is connected correctly, you
should see the audio levels start rising in Audalyzer. What you
want is for the average level of the audio to be around -10dB and
with a peak of no more than -5dB, so increase the audio control on
your playback device until you get to that level. This will mean a
little trial and error, but hey, this is analogue audio recording –
you’d have to do this regardless of what recording device you were
using. The trick here is that you won’t need the audio level very
high at all. If you go too far beyond this, you’ll overload the mic
input and simply record lots of what’s called clipping distortion
and you don’t want that.

When you’re set, switch your phone to PCM Recorder, press the
Record button and hit the Play button on your playback device. When
the playback audio is finished, press the Record button again on
PCM Recorder to stop recording. If you then play back that
recording on your phone, you should hear the audio you
recorded.

 

Audio Quality
Are we talking CD quality recordings here? No, definitely not.
We’re trying to squeeze line-level audio through a single-channel
(mono) mic input, so while it’ll work well enough for speech and
basic AM radio-quality music, it’s not going to replace your iTunes
collection. But don’t let anyone tell you it’s not possible to
record audio from an external source using a smartphone – you just
have to know how!