Draft:ABC System

• Comment: We generally look for at least 3 sources to prove notability; only two distinct sources grapesurgeon (talk) 10:53, 8 July 2026 (UTC)

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The ABC System was a quadraphonic matrix spatial sound system developed in the Soviet Union during the late 1970s by a research team led by musician and engineer Yuriy Berendyukov at the Leningrad Electrotechnical Institute of Communications. Developed through psychoacoustic research into human spatial hearing and phantom sound localization, the system employed a two-channel matrix encoding method intended to reproduce a continuous 360-degree panoramic sound field while remaining compatible with conventional stereo records and playback equipment. The system was adopted experimentally by the state-owned Melodiya label which released demonstration and commercial recordings encoded in the format.

Development

Development of the ABC System originated from research into the psychoacoustics of spatial hearing conducted by Yuriy Berendyukov at the Leningrad Electrotechnical Institute of Communications. In his dissertation, Berendyukov argued that multichannel sound reproduction should make maximum use of the listener's natural ability to localize phantom sound images throughout the full 360° azimuth. In a related patent, he identified the limited region of reliable localization provided by existing matrix systems as a principal shortcoming motivating further research.

To evaluate the spatial performance of existing quadraphonic systems, Berendyukov conducted controlled psychoacoustic listening experiments using SQ and QS matrix reproductions. Four loudspeakers were arranged in a square with a 2.8m speaker spacing and aimed toward the listener who was seated at the center. A recorded female speech narration served as the test signal, and the system was individually calibrated for each listener. Signal levels and phase relationships were adjusted using stepped attenuators, phase shifters, and switching elements to reproduce the operating conditions of the matrix systems under investigation. The perceived locations of phantom image zones were then recorded as three-dimensional (x, y, z) coordinates, providing quantitative data for the evaluation of spatial localization.

QS was found to produce stable front and rear-center phantom images but exhibited unreliable localization along the side speaker pairs, with the apparent front and rear soundstages reduced by approximately 50% and 30% respectively. SQ maintained the apparent width of the front and rear stages but was unable to reproduce stable phantom images at the front and rear centers without logic steering, causing those images to be perceived above the listener instead. Although logic-assisted decoders improved localization in some operating conditions, Berendyukov concluded that their effectiveness depended on the program material and that they introduced audible amplitude, frequency, and spatial distortions, making them only a partial solution.

Design

Based on these findings, Berendyukov concluded that the conventional square loudspeaker arrangement was not optimal for human spatial hearing. Through experimental investigations he determined that an isosceles trapezoidal loudspeaker layout, with the listener positioned near the rear loudspeaker base, provided reliable localization of phantom sound images throughout the full 360° sound field. These findings formed the basis of the ABC system's panoramic encoding method.

During encoding, individual program sources were processed by a panoramic encoder using variable coefficients ranging from −1 to +1. Rather than minimizing reconstruction error between the original and decoded channels or encoding for a completed four channel programming, these coefficients were selected to produce reliable localization of phantom sound images at any desired azimuth within the full 360° sound field. The encoded source signals were then combined into two transmission channels, allowing the system to remain compatible with conventional stereo records and playback equipment.

During playback, the encoded two-channel signal was decoded for reproduction through four loudspeakers arranged at the vertices of an isosceles trapezoid, with the listener positioned near or on the rear loudspeaker base. The recommended spacing between the rear loudspeakers was not to exceed 6 meters.

The system's name was created in reference to the three primary phantom image zones created between the speaker pairs. Zone A refers to the image between the front speakers, Zone B between the front-left and rear-left speakers, and zone C between the front-right and rear-right speakers. The recommended loudspeaker geometry and listening position were considered essential for maintaining these images. Moving toward the center of the trapezoid, such as in a traditional quadraphonic seating position, caused the side images to collapse and disrupt the continuity of the panorama.

Legacy

In a 2020 interview, Berendyukov recalled that a consumer music center incorporating an ABC decoder had reached the preparation stage and that the necessary technical documentation was being completed. He further recalled that development progressed slowly and, as international interest in quadraphonic audio declined, the project did not proceed beyond the 1980 release of the ABC-encoded album by his band, Yabloko.

Surround Matrix

Although the ABC encoder assigned variable coefficients to individual program sources, the published decoder consisted of a fixed four-channel decoding matrix. The decoding matrix published by Berendyukov and colleagues in Radio is shown below.

ABC System decoding matrix	Left Front	Right Front	Left Back	Right Back
Left Total	1.0	0	1.0	-0.7
Right Total	0	1.0	-0.7	1.0

Known Recordings

Квадра. Демонстрационная Квадрафоническая Пластинка По Системе ABC — Melodiya, КА90‑11199‑200 (1978) ABC System at Discogs

Яблоко – Кантри‑Фолк‑Рок‑Группа «Яблоко» — Melodiya, C60‑15499‑500 (1980) ABC System at Discogs