Monday, 2 April 2007

aa week 4 - mic techniques

The aim of this weeks exercise was to try out various microphone techniques for recording a consistent sound source. [1]

I set up a small radio broadcasting a tuning whistle, around this I set up an array of 6 microphones. (as above)

  1. AKG C414 - condenser mic set to OMNI DIRECTIONAL pickup pattern

  2. AKG C414 – set to SUPER CARDIOID

  3. Shure SM 58 – dynamic mic, CARDIOID pattern

  4. Shure BETA 52A – dynamic mic, CARDIOID pattern

  5. Sennheiser MD -421 – dynamic mic, CARDIOID pattern

  6. Sennheiser MD -421 – dyanmic mic, CARDIOID pattern

With this setup I could explore

  • proximity effect using the MD-421's. Both of these mics were pointed at the same point of the sound source, with one being approx 8 cm and the other 60cm distant.

  • differing polar patterns using the C414's. These mics were placed at similar distance and along the same axis.

  • differing microphones using the SM 58 and the BETA 52A. These were also place at similar distance and along the same axis.

Here are the six sound samples (these have been normalised)

01.mp3 02.mp3 03.mp3 04.mp3 05.mp3 06.mp3

There are noticeable differences in all samples.

The two MD-421 samples exhibit the tendencies of the proximity effect quite nicely.

There is a marked difference in sound with the more distant mic having a much thinner sound, and a much reduced volume (obviously the normalised samples do not :).

The two C414's sound qualities are again quite different, below are frequency analysis of them.[2]

The omni-directional (top) having more of a distinct peak at about 670 hz and the hyper-cardioid (bottom) having more balanced frequency distribution.

The two Shure microphones also show major differences in sound quality.

The SM58 having a broader sound.

Of the sounds recorded, the C414's surprised me the most - the difference is quite disctinct.
Whether this was caused solely by the differing polar patterns or the setup [3] could only be revealed through having two recordings from the same postion (this thought occuring to me several days after the recording session).

[1] Fieldhouse, Steve. Tutorial on Microphones. University of Adelaide, 27 march 2007.

[2] Steinberg Wavelab5 3D analysis.

[3] Using a mono signal coming through two seperate speakers (the AM whistle through a stereo cassette radio), introduces all sorts of phase issues when comparing two microphones in different locations. The two mono signals would interact and effect the sound depending on location.

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