recording sound using a smartphone is like a dog’s walking on his hind legs. It is not done well; but you are surprised to find it done at all.
After Samuel Johnson
The smartphone/iDevice is the preferred window to the world of many people – it’s small, it’s handy, it does everything. It’s always with you. And it will do field recording, of sorts.
The internal microphone is usually a noise cancelling microphone designed to favour nearby sounds over ones far away – usually by letting ambient sounds sneak onto the back of the mic capsule to cancel out the ambient sounds impinging on the front. You, being closer to the front and shaded from the back cancel out less. Crude, but it sort of works.
Use an external microphone, not the handset one
That’s not where you want to go as a field recordist, indeed if you could discriminate against your fumbling and breathing noises you’d be better off 🙂
You want to be able to use an external mic. Omni for general run and gun ambient drive-by recordings, and a directional/shotgun mic if you want to pick out a particular birds. To use the latter well you need to be able to hear what you’re doing. Shame, is one of the big failings of smartphone audio is that your can’t record and monitor at the same time. It’s not unreasonable, you rarely want to hear that much of yourself in a phone conversation.
You need an external adaptor lead to convert the 4 pole headphone socket to a stereo headphone + mono microphone connector, these are cheap enough on ebay
You can’t do stereo microphone recording this way, it’s mono only. The input provides plug-in-power to energise electret mic capsules, because this is the typical active device in a phone headset.
Testing frequency response and sensitivity
I tested the frequency response using Rightmark audio analyser, and it looks good enough
Going in with 1k tone at -67dBu and 150Ω source impedance the tone level was -32dBFS RMS and with the tone off the signal was -70dBFS RMS implying a self-noise of -105dBu [ref]44.1kHz sampling, 22kHz BW, PCM, manual gain using the app SpectrumView[/ref] Which is acceptable for urban field recording, though not stellar.
Big FAIL in the field – no monitoring
The big trouble, however, is that you can’t hear anything through the headphones, so you can’t aim a directional mic. Which makes the whole rig a bit crap to use in the field, and this doesn’t seem to be fixable.
There are other bits that grate – for instance the iPod doesn’t always pick up there’s an external microphone, so you can end up viewing the internal mic instead. Then there’s the usual rattiness of apps all round, about 1 in 30 times it just hangs outputting trash on the screen. In general, as a field recorder, smartphones suck. They can be used, but anyone who has used a real field recorder will miss the positive action of real buttons, real record level controls, real metering, and yes, being able to hear what they are doing.
Wild Mountain Echoes has a good summary of the sort of hurt associated with smartphone audio recording. Dr Johnson was right. It can be done, just not well.
Big WIN in the field – live spectrum display
Being able to watch a live sonogram using spectrumview is pretty awesome, and it’s a good sonogram, too, quite well suited to general bird sounds.
The best of all worlds, use a field recorder before the iPod!
It is not done well; but you are surprised to find it done at all.
Best not argue with Dr Johnson 🙂 As a recorder my iPod was flaky and with an input noise level some 20dB off what it could be and mono it’s nothing special even when it does record.
You can get the sonogram by feeding the iPod or smartphone/i-Device downstream of your field recorder – simply use a headphone y-splitter out of the recorder with one side going to your headphones and the other to the iDevice input, and set the gain of the iDevice waaaay down. You don’t have to record with it.
You now have a reliable recorder, decent mic preamps, you get to monitor what you record and if the iDevice throws a wobbly then you still have a good recording. But you how get a lovely spectrogram in live real-time. This is something that’s really excellent. In an ideal world the spectrogram would be built into the field recorder, however running it really hammers battery life so it’s good to have it optional. And it needs to be in colour.