Saturday, July 05, 2008

Using Equalization to Highlight Bird Calls

Posted by Philip Tyler

My goal was to capture early morning birds at a Reed Fen in the Titchwell RSPB Nature Reserve. Upon listening to the recording at home, the "roar" of the surf and the "rumble" of traffic on the coastal road seemed to interfere with the clarity of the bird sounds. Oddly enough, these sounds on the right channel (to the North) were louder than sounds from a village about the same distance to the left.

Using a narrow "Q" setting in the Parametric Equalization plug within Audition, I swept the frequency spectrum listening for bandwidths that seemed most obtrusive. I settled on moderate curves centered on three frequencies: 291 Hz, 862 Hz and 1770 Hz. I reduced the volume of these bandwidths 16 dB, 15 dB and 20 dB respectively. At 291 Hz there was an objectionable rumble. At 862 Hz there was a pronounced roar from the road and surf and there was excessive airyness around 1770 Hz.

I sent the original recording to Rob Danielson to see how he might handle the task of making the bird calls more apparent. He equalized the recording to his tastes and produced a QuickTime video comparing my EQ settings with the original recording, his EQ settings with the original recording and our EQ settings against each other.
Our results sound quite similar! I used only low frequency "cut" while Rob used a combination of attenuating low frequencies and boosting high ones. Rob also equalized the right channel differently to try to compensate for the heavier bass on the right side. The down side of the EQ that we used was lowered presence of the Collared Doves and Wood Pigeon whose calls were affected by the low frequency attenuation. I am pretty happy with the results and having Rob come-up with similar results is assuring. I'm convinced that if one is willing to spend time experimenting with EQ, you can get quite acceptable results.

My microphone rig was comprised of two "shotgun" Sennheiser ME66 mics in a crossed configuration angled about 25 degrees. The mics were powered and amplified by a Sound Devices MixPre and recorded on a Sony MZRH1 Hi-MD.