I've been experimenting with recording to an N900 with an external microphone. I soldered together an adapter for the multimedia socket to split a headphone socket (3.5mm, stereo) and a microphone socket (3.5mm, mono) from the 3 way socket on the device. Guess I could have used the video cable but hey...

Anyway, I've tried recording with a decent external microphone, and it works in that I get sound. However, I notice a strange artefact on the recordings, and testing with the device's built-in microphone reveals the same artefact, so it isn't the microphone.

I wondered why this happens, whether there is a way around it, or whether it is just a defect of the hardware.

Attached is a (very short) recording of a robin singing. If you listen carefully, you can hear the background hiss increase in volume at the same time as the bird whistles.

I guess there could be a few things that might do that - auto gain control, some form of audio compression (even though I recorded as WAV), or just the way the hardware is set up (which will be primarily for voice).

I get the same problem at 44.1kHz and 48kHz, and it doesn't matter which recording software I use (VoiceNote in this case). It also happens when recording video.


Anyone got an idea? Any weird alsa settings that might fix it? Am I just expecting too much from a phone?


On another note, it would be nice to monitor the input through the headphones, but I haven't found an app that will allow it. Maybe a command line hack with gstreamer would?

Thanks for any help.

If there are any good ideas for settings, I'll probably try and add a simple app for external microphone recording which utilises them.