Sunday, February 18, 2007

Equalization To Improve Spatial Transparency

I recorded some impulses from a frozen water main repair a half block away with Rode NT2000's in a parallel boundary rig with 2.5" inset using a Sound Devices 744T recorder.

Here's a link to the recording as a 256 kps mp3 after I equalized it:

The equalization I used is based on a +10dB "lift" 1000-4000 Hz with lower-mid "notching" of the resonant tones. The concrete crusher (which sounds more like a pile driver on the frozen clay) is on the other side of a brick, three story, apartment building. All of the sound waves from the equipment are indirect reaching the rig after reflecting from local surfaces. The difference in EQ used between the two channels above 4K stems partially from noise performance in the two mics-, but also from trying to balance the pronounced hiss from a gas meter that was mostly on one side. Blue = left channel and red = right (I flipped the output after EQ).

Here's a link to the original recording for comparison, roughly volume matched also as a 256 kbs mp3.

I believe it is easier to "visualize" the location of the concrete crusher in the equalized file. The complex "stuttering" echoes created by nearby building surfaces are also more evident. Rob D.

Tuesday, July 04, 2006

Rising Low Frequency Response

Example
Hi Rob -- On the WL183 and Low Frequency Response
All the mics I'm now using: NT4, NT1A, WL183 have extended bass response, which is good in comparison to the ECM909 I began with. But I notice that what is recorded with all three mics at lower frequencies is much more pronounced than I hear it myself: distant jet aircraft are more noticeable (a big problem where I live). ECM 959 and 999 don't seem so pronounced at LF.

When I look at the Wavelab FFT analysis screen when editing, I see that response goes down to almost dc levels, with NT1A having a hump from about 9Hz to just under 200Hz with a peak at about 40Hz. WL183 not so obvious but still enhanced.


[Spectrum image at top] is from the WL183s in a SASS setup, recording a few seconds of quiet woodland ambience. Does this show a rising LF repsonse to you, or is it an artefact of the analysis method perhaps?


I recorded a couple of music tracks indoors with theWL183 whilst on holiday - and these don't seem particularly bass heavy. Whereas outdoors, the extended bass is more noticeable. I realise this is all a bit hand-wavingly subjective, but I just thought I'd ask. As it is I tend to EQ out at the bottom end to return things to what I remember in the field.


Regards

Allan H

QuickTime Movie on Spatial Clarity 125-700Hz

Here's a QuickTime movie concerning posting techniques for field recordings added here for reference. It is the best example I've prepared to show some of the ways current recording technology are significantly challenged in reproducing sounds in this spectrum in "quiet," low-reverberation conditions and high mic preamplification is used.

If you encounter difficulties playing QuickTime movies with your browser or OS, you can right-click-download the movie in this directory (
titled: MicPreClarity125-700HzTest.mov) and use the free Video-Lan movie player to play it. Rob D.