Yes, you can use mobile phone as a sound recorder

November 3, 2016

In my previous blog post I wondered whether one can record anything usable on a mobile phone.

The answer was yes, but my Samsung S4 mini's internal noise gate ruined quiet recordings. The app I used for recording was (and still is) PVD Field Recorder, and soon after the blog post was published the developer of Field Recorder, Dr. Hartmut Pfitzinger, emailed me and told that it's very easy to bypass the noise gate: by choosing a preset "StereoAGCoff" the noise gate is switched off. At the same time some other parameters are changed too, e.g. an EQ curve is activated for the input with a little bit of boost in low frequencies and attenuation in highs to give a little bit of warmth to the harsh sound of the Samsung's mics and circuits.

Since then I've been using this preset setting whenever using the app for random recordings and it has worked fine, but haven't had time to do any real testing. Until today, when I was sitting in my room, had some spare time to spend and did nothing but listened to the silence around. So I finally decided to test the "AGCoff" preset in action, I grabbed my cello and started to play some quiet passages.

Here's a short recording of those notes. In this first clip I'm using PVD Field Recorder on the Samsung S4 mini with with the "StereoAGCoff" preset setting. (I did the recording in stereo, but decided to use only the right channel to match it to the reference track in the end of this post.)

As you can hear, no noise gate! The hiss stays constant and steady as it should. However there are those strange high snaps and clicks, which I haven't noticed before. I don't know what is causing them. I tested without the AGCoff preset, but they stay there. I tried with different sampling rates, but no difference. Maybe they are caused by some electric gadget in my room or a wifi router or something like that. Or maybe I've just dropped my phone too many times and now something has broken inside. I have to take a look at that later.

Back to the track: Now when the noise gate is not pumping the sound it's easy to apply some noise reduction. For the second clip I ran the recording through iZotope RX5 and used quite mild settings in its Noise Reduction tool. I also used the De-clipping tool to get rid of those strange snaps.

Not bad. With another pass the hiss could be reduced much more if needed. The sound is still a bit harsh despite the pre-EQ, but with further EQ'ing some beauty could be carved out of the raw material.

So definately my phone is now becoming something useful. Of course the small smartphone in my pocket is still a mile apart from proper recording gear, but on the other hand I can't make any phone calls or check the cutiest cat videos with my SoundDevice 702. And small phone is a brilliant tool for stealth recordings!

Finally, for a comparison here are the same notes recorded with an AT2035 large-diaphragm condenser mic into an RME Fireface UCX interface.