Spaced Pair Technique

The spaced pair technique is a microphone placement system to achieve stereo sound recording.

Of the three common techniques for stereo recording, the spaced pair technique is the one that achieves the greatest stereo width (above the coincident pair technique and above the nearly coincident pair technique).

Two or three identical microphones are placed horizontally apart, pointing in a straight line towards the source of the sound. Microphones can have any polar diagram, however, in this modality the most used pattern is omnidirectional. If, finally, omnidirectional microphones are used, they must be placed close to the stage to achieve an acceptable direct sound/reflected sound ratio.

In the spaced pair technique, what produces the stereo effect is the time difference in which the information from each of the two channels is received, thus allowing the spatial localization of the different sound sources. Central sources produce an identical signal. On the other hand, a source placed to one side will be closer to one of the microphones than to the other or others and, therefore, its sound will reach the closest microphone before the one that is furthest away. When reproducing the result, we are faced with two almost identical signals, with the exception that one signal is delayed (that of the far microphone) with respect to the other (that of the nearby microphone). When the delayed signal is reproduced, it is perceived as far from the center.

The further apart the microphones are, the greater the stereo width. However, the myth that microphones could be spaced as closely apart as the speakers themselves is false, since if the spacing is exaggerated, sound sources that are slightly off center can be reproduced as fully right or fully left, depending on the case.

To record with a good balance it is necessary to place the microphones approximately between 3 and 3.65 meters (10 to 12 feet) apart, but such separation is exaggerated, therefore, it is normal to place a third microphone halfway of the original pair and mix its output with both channels.

The advantage of using the spaced pair technique is that the resulting sound image produces a warm sensation of the environment; in the case of recording an orchestra, the reverberation of the concert hall seems surround the instruments and the listener himself.

Another advantage in using the spaced pair is that it counteracts the imbalance that occurs due to delay when the listener sits outside the center of the speakers.

The drawback of using this spaced pair technique (despite the stereo width achieved) is that when the image moves away from the center it tends to be vague and out of focus i> (i.e. difficult to locate). Although the objective is this: to look for rather diffuse sound images; Without a doubt, the spaced pair technique is the most indicated. In fact, this technique is widely used by special effects creators.

Another big problem with the spaced pair technique is that large phase differences can occur between both channels, which means that it is not monocompatible (certain frequencies can be canceled/or bibens/comb effect can occur) and that it cannot be edited. to cut (record-cutting).

The most used spaced pair technique modalities are:

• Omnidirectional spaced at 91 cm (Three feet). Two omnidirectional microphones are used and a fairly accurate sound image is achieved although the remaining sources outside the center are poorly focused. This would be solved by separating the microphones 60 cm (two feet) instead of 91 cm, achieving better location accuracy.
• Omnidirectional spaced at 3 meters (10 feet). By using two very separate omnidirectional microphones a large amount of stereo is achieved with uniform coverage.
• Omnidirectional spaced at 3 meters (10 feet) end to end. It uses three omnidirectional microphones spaced 3 meters extreme to extreme. The central micro is spaced horizontally 1.5 meters from the other two. It is thus achieved to maintain a great coverage, but reducing the separation of the stereo (empty signal in the center).