Redrafted Aim and Objectives

After researching into a few different 5.1 microphone techniques and finding out about Upmixing i have refined the concept of my project.

Aim:

To create a test to assess the qualities and preference between upmixing techniques and 5.1 microphone techniques. The test will be created specifically for the techniques applications in recording live events and performances. 

Objectives:

• Research 5.1 microphone techniques and Upmixing techniques and their applications in recording live music. 

• Record and mix live events and performances using 5.1 microphone techniques and upmixing techniques.

• Compile and then analyse the results of a listening of both 5.1 and upmixing techniques.

Research into Upmixing

Upmixing is a technique used to convert mono or stereo into 5.1 surround sound. This is an interesting technique to consider in relation to my project as it could mean the possibility of not having to record the event in 5.1 but rather in stereo and then convert it to surround sound. However the upmixing does not create a "true" 5.1 image but gives it a larger sense of space by adding information to the rear speakers of the 5.1 array.

• It would be interesting to consider testing a 5.1 recording with a stereo version that has been upmixed. The results would show wether people can tell the difference between the two techniques and which one is preferred by the listener. This would indicate wether it is worth going to the expense of recording an event in 5.1 or upmix a stereo recording. 

"There are lots of ways of expanding stereo material to 5.1, but most techniques are based on those developed for converting mono to stereo. The most common approach seems to be to allocate the original stereo channels to the left and right channels of the 5.1 array, and then derive centre and surround channels. The derivation of centre and surround channels may remain unchanged throughout the track (the usual technique for classical music), or may change — perhaps to emphasise specific sections, such as the choruses in popular music. Of course, by retaining the original left and right channels, the end-user can easily get back to the original stereo if they don't like the upmixed surround version.
Techniques vary widely, but the centre channel is typically a mono sum of left and right, possibly with a little equalisation and maybe a touch of extra delay. The surrounds are usually derived from left minus right (and vice versa), again with some delay and EQ, and possibly some extra reverb. Much hushed talk surrounds the production of upmixed 5.1 mixes from stereo, but as you can see, it's not really rocket science, merely a way of arranging material from a completed two-channel stereo mix such that it plays back over all six channels of a 5.1 playback system. There are also several products on the market now — such as TC Electronic's System 6000 — which incorporate dedicated algorithms specifically to convert stereo material to 5.1. The results depend on the source material, but often the upmixed version is very credible and pleasant to listen to."

You Are Surrounded, Surround Sound Explained- Part 5, Hugh Robjohns, December 200, Sound on Sound Magazine

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