Recording Audio on the Road

June 3, 2011 11:56 AM

I record conversations in my car, on my iPhone, using lavalier mics and the FiRe recording app, which has nifty settings for things like gain, compression effects, high pass and low pass filters, etc. I'm never happy with my results, though. Any recommendations for getting the best possible sound when recording in a car? (If mentioning filters and such, specific numbers or ballpark ranges would be great.)
posted by Pants McCracky to Technology (6 answers total)

I recommend not doing any filtering live, unless you need the audio right away. Filtering is a destructive transformation; if it's done live, you can't take the filter off later.

Instead, you can open up your recording in Audacity after the fact and use the nifty Noise Removal filter, where you select a period of the recording with no speech (so presumably just background car noise) to get the "noise profile" and it automatically picks up the attributes of the noise (i.e., characteristic frequencies) and removes them from the entire recording.

In general, you want the microphones as close to your source (i.e., your mouth) as possible, and set your input volume as loud as possible such that your loudest speech wouldn't cause the input level to peak.
posted by supercres at 12:02 PM on June 3, 2011

I recommend not doing any filtering live, unless you need the audio right away. Filtering is a destructive transformation; if it's done live, you can't take the filter off later.

Oh, I forgot to mention, my situation is such that I put the audio online right away, at work, and don't have the opportunity to do any post-recording filtering. So, even though it's sub-optimal, I'd like to process the audio live for the best results I can under the circumstances.
posted by Pants McCracky at 12:21 PM on June 3, 2011

I've been using the ClearRecord Premium app for short recordings and the noise reduction it does on the fly is pretty amazing. No idea how it compares to your existing setup but I have been blown away by how clearly it records via the built-in mic in sub-optimal placements.
posted by phearlez at 12:25 PM on June 3, 2011

In that case, if you want a fixed-frequency filter, you might get the most mileage (so to speak) out of a 80-3000 Hz bandpass filter; human speech falls within that band. (If you're only recording women, you can go up to about 150-3000.) I'm guessing that most of the car noise is low-frequency, so the highpass part of the filter will be the most helpful.

Or use an app with automatic filtering, as phearlez suggests.
posted by supercres at 12:33 PM on June 3, 2011

Try quick attack and release on the compressor. Have the compressor have a steep curve (10:1 ratio or so), but only have it kick in with about minus 10 dbs or from 0.

Use the high pass filter as supercres mentioned. Gain is dependant on whether or not it's a 16 bit or 24 bit recorder. As well, see if there's an auto-normalize feature after recording. This alone could add about 5 or more dbs to your recording which is partly why you may currently find it to be too quiet.
posted by fantasticninety at 1:15 PM on June 3, 2011

EDIT - "with about minus 10 dbs or SO from 0"
posted by fantasticninety at 1:15 PM on June 3, 2011