Research into Microphone Techniques

I have been reading an Audio Engineering Society Convention Paper which discusses 8 different surround microphone techniques used for live orchestral recordings. The paper discusses the results that were gathered from a subjective listening test where the subject could freely listen to each microphone technique which were assigned separate sliders, enabling the subject to rate the techniques simultaneously.

Audio Engineering Society Convent Paper 7233, 
Correspondence Relationship between Physical Factors and Psychological Impressions of Microphone Arrays for Orchestra Recording,
Toru Kamekawa, Atsushi Marui, and Hideo Irimajiri 
October 2007

I will be using this paper to find out what microphone techniques i should use in my project as they are being applied in a similar situation of a live performance. The 8 microphone techniques discussed and tested in this paper are:

1. Fukada Tree (Fukada) 

2. INA5 (INA)

3. Double MS (DMS) 

4. Omni+8 (OM8)
5. Decca Tree + Omni Square (DT+OSQ) 

6. Decca Tree + Hamasaki Square (DT+HSQ) 

7. Five Cardioids + Hamasaki Square (5C+HSQ) 

8. Three Omnis + IRT Cross (3O+IRT)

The subjects in the listening test (13 students and 9 recording experts) were to evaluate each microphone technique by seven different attributes:

1. Spaciousness: The width of frontal image. 

2. Envelopment: The enveloped feeling surrounded lateral and backward

3. Depth: The apparent spatial distance of the sound source from the listener.

4. Localization: The apparent location of the sound source.

5. Powerfulness: Strong or heavy impression. Opposite meaning is week or feeble.

6. Softness: Mild or silky impression. Opposite meaning is hard or harsh. 

7. Preference

The averages of the test results showed that the Decca Tree plus Omni Square (DT+OSQ) technique rated the highest on all attributes. The results also showed the Double Mid-Side (DMS) technique rated the lowest on all attributes. 

From the results in this listening test it is clear to see that the DT+OSQ was the highest rated and should be applied in my project. However this test was on recording a live performance from an orchestra with no audience, which means the space was available to them to place microphones wherever they needed to be in the room without having to compromise placement because of an audience. Unfortunately i will not be able to employ DT+OSQ technique because space will be a factor during the recording in my project and to use this technique i would have to place microphones above or in the audience, that will not be an option because of health and safety factors and i am also limited by the equipment available to me. 

Because microphone placement could be compromised by the audience and room layout of the venue during the recording process of my project i have decided to use small spaced surround arrays instead of large spaced arrays which need a large area for placement. 

The small spaced arrays that were tested in discussed in the AES Paper included the INA5, Double Mid-side and IRT Cross. The DMS technique scored very low on all attributes as well as the INA5, however the INA5 did score relatively high on Localisation. The IRT Cross technique scored relatively high on all attributes and from what i gathered from the listening test results it was the 3rd "best" after the DT+OSQ and DT+HSQ techniques in terms of it being even across all 7 characteristics. Thus i will definitely be applying the IRT Cross in my project, however i will research further into all three small spaced arrays i found in this AES Convention Paper. 

Further Research:

• Practical based research- Do some practice recordings with the INA5, DMS and IRT Cross techniques
• Research more into small spaced arrays and other 5.1 production techniques