Friday, March 14, 2008

What mics are good for recording quiet subjects & spaces?

Budhaditya wrote on the Phonography list:
"I would like to hear from you abou
t the critical choice of microphone in field recording, specifically for capturing quieter sounds..."

I can get you started on researching this question. The rule of thumb for recording subtle sounds and ambience in quiet locations is to use mics with no more than 16dB(A) self-noise. Here's a list [htm] of suitable mics that I compiled and is reasonably complete. (Other lists)

Your Soundman OKM II K binaural mics "spec" with 32 dB(A) "self-noise" which is better suited for recording in loud enviroments and louder effects. Used In quiet places where the gain has to be increased considerably, the mics' self-noise will contribute audible hiss regardless of the recorder used. Should you be happy with the Soundman mics, you can consider buying a less expensive recorder because the high self-noise will always "mask" or cover-up the very low-noise performance of the mic preamps in the Fostex FR2-LE and Sound Devices 700 recorders. You Sennheiser MKH-416 mic requires phantom powering though which these two recorders provide. Your MKH-416, with 13dB(A) self noise, should be a lot quieter than the Soundman mics.

Your Soundman OKM II mics may require what is called "Power In Plug" or "PIP" in which the sound recorder supplies the DC voltage to run the mics through the 3.5mm stereo mic input jack. The Fostex or SD recorders don't have this input. Their XLR type connectors supply 24/48 volts phantom for condenser mics. You can buy or build an power adapter to run the Soundman mics on a SD or Fostex recorder.

Nature recordists tend to do ambient or "diffuse field" recording pretty regularly and the largest group/Listserv of such recordists has an archive with a lot of relevant discussion you can search & read.

To save you some reading time, below are some searches, by model number, of omni-directional mics that are frequently discussed on the list:

Phantom-powered, omni-directional mics for recording ambience in quiet places:
Audio Technica "AT-3032" Inexpensive. Surprisingly, low self-noise.
Senheiser "MKH-20" popular, expensive mic. Newer model is MKH-8020
Senheiser "MKH-800" Popular more expensive, multi-pattern mic.
Rode "NT2000" mid-priced, multi-pattern mic. Heavy.
Senheiser "MKH-30" Expensive. Used primarily as the "side" mic in "MS Pairs"

For small mics with a litle less self-noise, the Shure "WL183" [23dB(A)] and the Danish Pro Audio DPA 4060 [23dB(A)] are popular. The DPA mics are small enough to fit inside of the ears. For small mics with sunstantially less self-noise,~14dB(A), the Telinga "EM-23" or "EMKS-23" mics can be made in a fairly small package for PIP. Klas Strandberg ,who is currently the only source for this EM-23 configuration, might have to be coaxed into making them and they are not cheap. As the Primo EM-23 capsules can be purchasd (sans FET) for $60 each, folks on the MicBuilders list are currently trying FET options to achieve similar results. Here's a comparison test with some of the popluar small, electret mics people are using. If you are curious, the self-noise of your Soundman mics "spec" similar to that of the WM-61A's in the test.

Searching the models terms I put in quotes will get you started. Another very important factor is the "stereo"array" used and also shock-mounting and wind-protection. Curt Olson's simple to make wooden Stereo Mic Rigs are certainly worth a look and listen. Walt Knapp has some good photos of popular MS pairs using Sennheiser mics. Rob D.

Tuesday, March 04, 2008

Attenuating Louder Tree Frogs

Debbi would like to bring-out the subtler, quieter calls of Reg Legged Frogs in a recording where Pacific Tree Frogs are singing much louder. If equalization proves to help, she may decide to work on learning some EQ skills. To get the ball rolling, I've made a QuickTime Movie with four sound clips with my first attempt at EQ and EQ with an effects plug designed to reduce sibbilance. Here's description of the four clips in the movie:

(1) Debbi's original mono field recording.

(2) The recording equalized with 28 bands of parametric EQ using Eqium. I primariy addressed the raspiness of the tree frog calls in the upper mid-range, exaggerated high frequencies and I tried to address a mysterious very low frequency throbbing sound (idling truck?).

(3) The above equalization AND the "De-Essing" plug in Logic Audio (mild high hat setting). This plug was set to apply compression around 2K Hz.

(4) Debbi's equalized sound file she made in Audition.

I tried a number of ways to reduce the very low frequency throbbing in the recording without much success. I elected to leave it as is rather than eliminate it with a high-pass filter.

What do you think Debbie? Which of the four clips best serves your purposes? Rob D.