Finding an Appropriate Microphone Array

The proposed research project involves finding literature that discusses and compares 5.1 microphone arrays in order to find a suitable array to apply in this project. Kamekawa, Marui and Irimajiri created an experiment that compares eight 5.1 microphone arrays and their application in orchestral recordings. The subjective listening test compares the arrays on seven different attributes such a powerfulness, spaciousness and Localisation. This paper is pertinent to the proposed research because it compares the microphone arrays simultaneously.

“There are a lot of reports introducing methods and ways to record surround sound. However, it has been very difficult to compare between multiple microphone techniques under the same condition due to one or more of the following constraints; namely, the cost of collecting a large number of microphones in one hall on one day, time and space constraints of setting up all microphones on a stage, and mixing timbral/spatial differences created by different microphone techniques.” (Kamekawa, Marui and Irimajiri 2007)

A true comparison between recording techniques can only be achieved if the techniques are recorded simultaneously, this will be the same for the proposed research; both the 5.1 microphone array and upmixed stereo version will be produced simultaneously. Kamewaka, Marui and Irimajiri’s listening test also employs the same kind of method. Inspired by MUSHRA (Multiple Stimuli with Hidden Reference Anchor), each array was assigned to a slider on a mixing desk, allowing the test subject too listen and switch between each microphone technique simultaneously. This meant that there was no specific Anchor or reference. This method should also be employed in the proposed investigation, thus eliminating the need to play each technique separately and the possibility of the listener preference choice being influenced by the order of each technique being played.

Kamekawa, Marui and Irimajiri provide an extensive analysis of the results gathered from the subjective listening test that thirteen students and nine recording experts participated in. It is the analysis of these results that will form part of the rationale behind the choosing of a specific microphone array to employ in the proposed research project. The results showed that across three different orchestral pieces, the Decca Tree plus Omni-Square array scored the highest on all seven attributes with the Decca Tree plus Hamasaki-square coming second. However Kamewaka, Marui and Irimajiri state in their evaluation of the project:

“The result of listening experiment shows that each microphone array has different character and it is related to the configuration of each microphone array. Furthermore these characters depend on impression of the character of music.” (Kamewaka, Marui and Irimajiri 2007)

This shows that there are no “rules” behind the choosing of an appropriate microphone array because each reacts differently to the character of music and placement of the array. Not only this but also constraints such as space and the availability of equipment can influence the choosing of a suitable microphone array. Thus it is down to the competence of the sound engineer/researcher to choose the appropriate microphone technique to test against the upmixing technique in this project.

In light of what Kamewaka, Marui and Irimajiri’s experiment showed, the proposed researcher has chosen to employ the IRT Cross (cardioid microphones space 17cm apart with a 110^o angle); this array was considered third best across all attributes in Kamewaka, Marui and Irimajiri’s experiment. It has also been said it makes a good compromise between the factors of stereo image, dynamic range, liveliness and timbre. (Mason [no date]) (ceoen 1972) The IRT Cross also takes up little space and can be placed around the venue without any potential to risk health and safety. The use of far spaced arrays, such as the two techniques that scored highest in Kamewaka, Marui and Irimajiri’s experiment, would not of been appropriate to use in this project as it could risk peoples health and safety; microphones would have to be placed in or above the crowd at the event, which leaves the potential for injury. 

The IRT Cross has a 'brother' array which is very similar called the ORTF array, the difference between the two is one is rectangular and the other is square: 

IRT Cross

 http://www.schoeps.de/en/home 2013

ORTF

 http://www.schoeps.de/en/home 2013

Ceoen Carl. 1972.

Comparative Stereophonic Listening Tests

RadiodifJusion-Television Belge, Brussels, Belgium

Mason Russell. [No date]

Microphone Techniques for Multichannel Surround Sound

Guildford, UK

Irimajiri Hideo, Kamewaka Toru and Marui Atshusi. 2007.

Audio Engineering Society Convention Paper 7233:

Correspondence Relationship between Physical Factors and Psychological Impressions of Microphone Arrays for Orchestral Recording

New York, NY, USA