Week 6 -Stereo Techniques

In this weeks recording techniques lecture we focused on stereo techniques.

The 3 main stereo techniques for our assessment are:

1. AB stereo technique (spaced Omnis) – This is when omnidirectional microphones are spaced a few feet apart. The positioning is important if the mics are spaced too far there will be a hole in the middle of the stereo. If a hole is evident a 3rd mic can be added in the center (similar to a Decca tree techniques, though the recording techniques is conventionally done with only 2 microphones), but that might cause problems with phasing, so positioning of microphones must be done carefully. Another important aspect of positioning is how far is the musician going to be to achieve a nice balance of sound being picked up. If the sound is ambient the mics might need to be closer to the musician, however if the sound is too dry the microphones are probably too close to the musician. Be care with distances as this can significantly change the sound.

AB

PowerPoint made AB recording technique.

2. MS (mid side) stereo technique (We worked on this a lot last week) – This techniques is what you call a coincident techniques (this is when the microphones are positioned together) this creates a center image for the stereo. This is directional is the way it picks up sound. The techniques uses one side microphone, which is always a microphone with the polarity of figure of 8 (bidirectional) and generally the middle microphone is a omnidirectional microphone, but other combinations can be used (reference week 5). The middle microphone gets the center sound of the stereo in mono and the figure of 8 picks up the left and right in stereo. The side microphone is panned left and right. (reference week 5 for more information as this is heavily involved).

Mid Side

PowerPoint made diagram of MS technique.

3. Decca Tree stereo technique – This recording techniques uses 3 onimdirectional microphones. This is similar to the AB techniques however a third onmidirectional microphone is added to the center, so that there isn’t a hole in the mix. The 3 microphones are positioned in a equal triangle spaced about 60 cms parts. This recording technique is great for capturing an acoustic sound, so is really good for recording vocals and piano.  This technique can not be too wide as there will be a hole in the middle.

Decca Tree

Decca Tree made with Powerpoint.

The other recording techniques are as follows:

4. XY stereo recording technique – This is another coincident recording technique, which is when the microphones are close together. The capsules as close as possible. This recording technique is widely used in recording. It is when two cardioid microphones(and in less conventional cases even 2 figures of 8 (Blumlein recording technique) are placed at 90 degree angle to each other because they are directional mircophones one microphone will pick up one side and the other will put up the other side. Creating a nice stereo image. The reason why figure of 8s are sometimes used is because it will capture the left and right rears, this can be good for recording audiences and reverb. This technique does not mimic the human perception of hearing like the AB technique, however because the cardiod microphones have poor high frequency response it has the simulation of human hearing.   One big advantage of any coincident technique is that because there is no space there are no phase problems, however it can make the stereo effect seem weaker and the center image will not be as clear as the sides.

xy-stereo-microphone-recording

5. Blumlein recording technique – Okay. This is a XY stereo technique, however it uses the 2 figure of 8 mircophones. As I discussed in XY. The reason why figure of 8s are sometimes used is because it will capture the left and right rears, this can be good for recording audiences and reverb. The recording technique can be used in short distance. When recording at this distance it has what technicians call the proximity effect, which is when bass frequencies boost in the recording when the source is really close, however when recording in a larger distance those bass frequencies are lost.

Blumlein_-Stereo

6. NOS recording technique – This stereo technique uses 2 cardioids at a 90 degree angle. They are generally spaced about 30cm apart. This creates a stereo, which is affected by the proximity effect. When recording at this distance it has what technicians call the proximity effect, which is when bass frequencies boost in the recording when the source is really close, however when recording in a larger distance those bass frequencies are lost. This technique is technique is good for recording piano, or a small ensemble and creating a stereo image for a orchestra.

2000px-NOS-Stereo.svg

7. ORTF stereo technique – This technique has the microphones positioned in human hear (ear distance) about 17cms. This as a wider stereo than XY, while holding the mono info. The microphones both being cardioids at angles of 110 degrees. This recording technique is meant to be mimic human hearing. This technique is also under the influence of the proximity affect.

800px-ORTF-Stereo

8. Phrased array – This is a rarely used technique. What it basically is a AB stereo recording technique using 2 figures of 8 (bidirectional) microphones. The distance must be extactly 23 cms. This was invented by Tony Faukner.

Phrased array.

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