A one-dimensional two-channels stereophonic standard

Recently it has been archieved to capture, store, propagate and play back audio with the full human hearing frequency range (16 to 16000 Hz) and contrast (7 Bel). Still, if a big sound source or several sound sources at once are the matter of content, such play-back sounds artificial, because all is emitted from one acoustic source. In order to hear, what is going on, we use both ears simultaniously, turn our head in different directions and will detect the electro-acoustic device.

While an indetectable electro-acoustic reproduction incorporated six microphones, storage and transmission channels and a house-sized sphere covered by loudspeakers on the inside and containing the listener, we can help imagination at least a little bit by introducing sonic differences between left and rite. We also want this stereo, after Greek stereos shape, to integrate thoroly and easily with already existing mono electro-acoustics. We may double transmission and storage channels, for example by using vertical stylus movement or a frequency-shifted band for L-R information, while L+R is on the old mono channel.

This is one-dimensional stereophonics, which has two electric channels encoding any sources placed at the horizon in front of the listener.

Because mono devices must not play a stereo record back worse than a mono one, stereo recordings must have both channels in sync. This can be done by picking up both channels in the same acoustic spot. Co-incidence also known as synkronous and intensity-stereo microphonics does this. Two cardioids at rite angle record well front hemisphere (196 2pi-is-360-degrees degrees) in stereo.

Because stereo devices must not play a mono record back worse than a stereo one, stereo playback must have both channels in sync. This premise is hard to fullfill with loudspeakers, because run-time between loud-speaker and ear is rarely the same for a left and a rite loud-speaker, and never for both ears and both loud-speakers at the same time. Just two loud-speakers cannot do stereophonics.

A possible kind of play-back, which is rather easily done, is a pair of head-phones. As our brain uses phase difference between left and rite ear for localisation, our synkro-stereo as pressed on vinyl and broadcast with FM results in only a weak stereophonic impression. In order to improve it, we tap each channel, lopass-filter (just like our head shades sonic waves from left for rite ear) and delay (just like sonic waves from left reach rite ear later) the tap and add it to the other channel. This processor is mono-compatible, because it processes all signals just with head transfer function. It must become adjusted to head size.

For loud-speakers stereophonics one needs a concave array of many loud-speakers, each getting a special grade of +-xL+-yR. There are ruffer and finer estimations: A x large curve consisting of y many loud-speakers can put out stereophonics, if x and y are sufficiently large. In order to keep cancellations above hearing range, the farer the listener is allowed to move to the side, the larger the product of x and y must be. Even with an infinitesimally finely resolved array there are still interferences, just like a line source has peaks and dips off-axis. Also, power may be wrong:

Three loudspeakers, for you know left, center and rite one, driven by Elias' power preserving matrix with sides further attentuated in order to further improve center playback, is not perfect but a start. This can be done passively and easily; connect an Y circuit with Z=8R eta=0dB sides and Z=2R eta=+6dB center to a two-channel amplifier with common ground.

Another trick is mirror-stereo, which radiates center sound from one spot but beams each side to its side. The stereo impression is archieved in conjunction with reflective (mirroring) side walls of the room, in whom the listeners are in. I designed GA13S, which flavours clean mono with a grain of stereo. Many radios do ruff mirror-stereo.

Monophonics and mono-compatible stereophonics in a nut-shell:
* Co-incidence-stereophonic recording with two microphones, or monophonic recording
* Transmission of at most two channels, obligate L+R and optional L-R
* Most efficient play-back over a head-phones processor and a pair of head-phones, or mono head-phone(s)
* More social and grounded play-back over loud-speaker(s), either for proper stereo a large array at a dedicated place, for casual stereo a three-loud-speakers or mirror one, or a mono loud-speaker