Sunday, January 04, 2009

One point stereo A-B?

While researching audiophile labels on the web I came across Waon RECORDS. Their offerings look interesting although most of the website is in Japanese only, which sadly I can't read.

Besides session snapshots the website informs that their recordings have been produced using "One point stereo A-B". This is an incorrect use of the term.

AB-stereophony takes it's name from a line connecting the most likely distinct points "A" and "B". It is runtime based, which means it employs differing time-of-arrival cues / phase differences embedded in the signals arriving at both microphones. Quite obviously this requires that the locations of the capsules are spatially distinct.

When you separate the microphones by about 50 cm a signal coming from one side of the configuration arrives at the opposite microphone delayed by about 1.5 msec, which, according to the rule of the 1st wavefront, results in it being localized towards the side of the speaker which first emitted it.

One-point stereophonic recordings can only be the result of coincident setups, where both capsules occupy (approximately) the same spot in space. This goes for XY (with two cardioid capsules), Blumlein-stereophony (with two bidirectional / fig-8 capsules) and M/S (with one bidirectional and usually one cardioid capsule).

This is not to say that you can't craft great recordings using a spaced pair of omnidirectional microphones. Well designed and built omnis can be extremely precise in the temporal domain, have a linear frequency response, don't colour sound arriving off axis and don't exhibit a proximity effect. Used in quiet, good sounding venues they can be used to capture the depth of the space very convincingly. Localization is impaired when compared to coincident setups, but that is a compromise the recordist might want to make.


Blogger Andrew Levine said...

I just got feedback from Kazuhiro Kobushi @ Waon Records explaining that he agrees with me. It is just that in Japan "one-point-stereo [...] just means 'it's NOT multi-microphones techniques'."

05 January, 2009 10:55  

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