UC (noise reduction)

The UC compander system (with "UC" derived from Universal Compatible or Universal Compander) is a noise reduction system for vinyl records, aiming at highest playback compatibility even without corresponding UC expander.

The UC compander system was developed in the 1980s by VEB Zentrum Wissenschaft und Technik (ZWT) of VEB Kombinat Rundfunk und Fernsehen [de] (RFT) in the former German Democratic Republic (GDR). The system was based on the observation that the dynamic range of typical audio source material almost always needs to be reduced in the vinyl mastering process and that very similar system parameters are commonly applied in the process either by the sound engineer or through the hardware. The idea was to develop a compander system loosely emulating this process and to formally standardize on its characteristics. By emulating the typical characteristics of this compression, UC compressed records would not produce acoustical artifacts which would not have been present in similar form on the produced disk anyway, and that thereby they would remain virtually unrecognizable, so that consumption would remain acoustically pleasing and compatible even if records were later played back without UC expander. Initial experiments with a compression factor of 2:1:2 were found to still cause too many artifacts to maintain this compatibility, which led the UC developers to implement a broadband compander utilizing an adaptive compression factor between 1.33:1:1.33 (or 1.67:1:1.67) (at 0 dB) and 1:1 (at −20 dB). In contrast to earlier vinyl disk noise reduction systems such as dbx disc, High-Com II or CX 20, the system deliberately limited the reduced disk noise by about 10 to 12 dB(A) only, an amount similar to what could be achieved by other compander systems where only the receiving side of the medium was exposed to users and therefore the system had to remain playback compatible with a large installed base of devices without corresponding decoder (such as Dolby FM or High Com FM in radio broadcasting).

In fact, the results were found so good that, especially for records produced with Direct Metal Mastering (DMM) (but not exclusively), the system was undocumentedly introduced into the market by the East-German VEB Deutsche Schallplatten through record labels such as Amiga, Eterna [de] and Nova since 1983/1984, with UC-encoded records only identifiable by a shy extra "U" engraving in the disk's silent inner groove area. Up to 1990, over 500 UC-encoded titles were produced.

The economical necessities in the former GDR, however, made it impossible to introduce a suitable UC decoder at the same time. Prototypes of a HMK-D100-based tape recorder with digital counter and UC expander seem to have existed in 1987. Finally, a UC expander was built into the Ziphona HMK-PA2223, a tangential arm direct drive turntable manufactured by VEB Phonotechnik Pirna/Zittau in limited zero batch quantities only around 1989. The expander was based on a RFT/HFO A274[D], the East-German equivalent to the voltage-controlled electronic potentiometer IC Valvo [de]/Philips TCA740[A].

The German reunification and the advances in digital home audio equipment put an end to the further introduction of the system in 1990.

Given the revival of vinyl records, the re-introduction of UC and the development of corresponding compander hardware based on modern semiconductors has been considered several times around 1994/1995 and 2009/2010.

A software decoder for UC has been implemented.

• dbx disc
• CX (Compatible Expansion)
• High-Com II
• RMS (Rauschminderungssystem), an unrelated tape noise reduction system used in the GDR in the 1980s
• Vinyl disc noise reduction systems

• Milde, Helmut (1986-04-02) [1985-01-02]. Schaltungsanordnung für einen Breitband-Kompander [Circuit arrangement for a broadband compander] (PDF) (in German). Dresden, Germany: VEB Zentrum Wissenschaft und Technik. ISSN 0433-6461. Patent DD234549A1. Archived (PDF) from the original on 2021-05-07. Retrieved 2021-05-07 – via Amt für Erfindungs- und Patentwesen. [11][12] (4 pages)
• Milde, Helmut; Eras, Heinrich (1987-01-28) [1985-10-24]. Kompressor-Expander-System für elektroakustische Übertragungswege [Compressor expander system for electric acoustic transmission paths] (PDF) (in German). Dresden, Germany: VEB Zentrum Wissenschaft und Technik im VEB Kombinat Rundfunk und Fernsehen. ISSN 0433-6461. Patent DD242517A1. Archived (PDF) from the original on 2021-05-07. Retrieved 2021-05-07 – via Amt für Erfindungs- und Patentwesen. [13][14] (6 pages)
• Milde, Helmut (1987-01-28) [1985-10-24]. Kompressionseinstellstufe für einen Breitbandkompander [Compression setting level for a broadband compressor] (PDF) (in German). Dresden, Germany: VEB Zentrum Wissenschaft und Technik im VEB Kombinat Rundfunk und Fernsehen. ISSN 0433-6461. Patent DD242518A1. Archived (PDF) from the original on 2021-05-07. Retrieved 2021-05-07 – via Amt für Erfindungs- und Patentwesen. [15][16] (3 pages)
• Milde, Helmut (1988-06-16) [1986-12-11]. Kompressionsgradeinstellstufe für einen Breitbandkompander [Compression level setting stage for a broadband compander] (in German). Dresden, Germany: VEB Zentrum Wissenschaft und Technik. Patent DE3642363A1. Archived from the original on 2021-05-07. Retrieved 2021-05-07. [17][18]
• Milde, Helmut; Eras, Heinrich (1988-06-16) [1986-12-11]. Kompressor-Expander-System für elektroakustische Übertragungswege [Compander system for electro-acoustic transmission paths] (in German). Dresden, Germany: VEB Zentrum Wissenschaft und Technik. Patent DE3642366A. Archived from the original on 2021-05-07. Retrieved 2021-05-07. [19][20]
• Bergmann, Heinz (November 1982). "Verfahren zur Rauschminderung bei der Tonsignalverarbeitung" (PDF). radio fernsehen elektronik (rfe) (in German). Vol. 31, no. 11. Berlin, Germany: VEB Verlag Technik [de]. pp. 731–736. ISSN 0033-7900. Archived (PDF) from the original on 2021-05-05. Retrieved 2021-05-05. (NB. Page 736 is missing in the linked PDF.)
• https://web.archive.org/web/20210506190336/http://forum.rft-radio.de/thread.php?threadid=1066