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The High Com (also as HIGH COM, both written with a thin space) noise reduction system was developed by Telefunken, Germany, in the 1970s as a high quality high compression analogue compander for audio recordings.
The idea of a compander for consumer devices was based on studies of a fixed two-band compander by Jürgen Wermuth of AEG-Telefunken ELA, Wolfenbüttel, developer of the Telefunken telcom c4 four-band audio compander for professional use. In April 1974, the resulting "RUSW-200" prototype led to the development of a sliding two-band compander by Ernst F. Schröder of Telefunken Grundlagenlaboratorium, Hannover since July 1974. Finally, the released High Com system, which was marketed by Telefunken since 1978, worked as a broadband 2:1:2 compander, achieving around 10 dB of noise reduction for low and up to 20 dB A-weighted for higher frequencies, while avoiding most of the acoustic problems observed with other high compression broadband companders such as dbx.
In order to facilitate cost-effective mass-production in consumer devices such as cassette decks, the compander system was integrated into an analogue IC, TFK U401B / U401BG / U401BR, developed by Dietrich Höppner and Kurt Hintzmann of AEG-Telefunken Halbleiterwerk, Heilbronn. With minimal changes in the external circuitry the IC could also be used to emulate a Dolby B-compatible expander as in the DNR (Dynamic Noise Reduction) system for backward compatibility.
Nakamichi, one of the more than 20 licensees of the High Com system, insisted on using a sliding-band compander, so High Com was further developed into the two-band High Com II and three-band High Com III sliding-band 2:1:2 systems by Werner Scholz and Ernst F. Schröder of Telefunken and Harron K. Appleman of Nakamichi in 1978/1979. This variant was eventually released as Nakamichi High-Com II Noise Reduction System in 1979/1980, increasing the amount of noise reduction on analogue recordings and transmissions by as much as 25 dB A-weighted.
Besides Telefunken's own CN 750 High Com compander box and Nakamichi's High-Com II unit, other companies also offered external High Com compander boxes such as the Aiwa HR-7 and HR-50 or the Rotel RN-500 and RN-1000. A low-cost implementation of the Telefunken High Com system as external compander box became available as HobbyCom, promoted for do-it-yourself assembly in the popular WDR TV series Hobbythek format by Jean Pütz in 1980.
Similar to the earlier Dolby FM system in the USA, a High Com FM system was evaluated in Germany between July 1979 and December 1981 by IRT. It was based on the High Com broadband compander, but was never introduced commercially in FM broadcasting.
While originally designed for tape recordings, Nakamichi demonstrated the usage of High Com II on vinyl records as well in 1979. In 1982 the same AEG-Telefunken team, who designed the High Com noise reduction system, also developed the IC U2141B for the CBS Laboratories CX noise reduction system for vinyl records.
While implemented in dozens of European and Japanese consumer device models and acoustically much superior to the Dolby B and C systems, the High Com family of systems never gained a similar market penetration. This was caused by several factors, including the existing pre-dominance of the Dolby system, with Dolby Laboratories introducing the "good enough" Dolby C update (with up to 15 dB A-weighted improvement) around 1980 as well, and also by the fact that High Com required higher quality tape decks and tapes to work with in order to give satisfactory results. High Com II even required calibration of the playback level using a 400 Hz calibration tone for optimum results, and with prices in the several hundred dollars for the external Nakamichi compander box it was much too expensive to be used by many people outside the small group of audiophiles using high-end tape recorders or open-reel decks. When AEG-Telefunken struggled financially in 1981/1982 and the Hannover development site was partially disbanded and refocused on digital technologies in 1983, this also put the High Com development to an end. The latest tape decks to come with High Com were produced around 1986.
- Dolby noise reduction system
- Dolby SR (Spectral Recording)
- dbx (noise reduction), a rival system
- Dynamic Noise Reduction (DNR), a playback-only noise reduction system often confused with Dolby
- CX (Compatible eXpansion by CBS)
- Schröder, Ernst F. "The Story of HIGH COM". Archived from the original on 2016-04-16. Retrieved 2016-04-16.
- HIGH COM - The HIGH COM broadband compander utilizing the U401BR integrated circuit - Semiconductor information 2.80 (PDF). AEG-Telefunken. Archived (PDF) from the original on 2016-04-16. Retrieved 2016-04-16.
- Nakamichi (1979). The Stillness of Dawn - High-Com II Demonstration Record. NAK-100. A limited edition not-for-sale High Com II encoded audiophile vinyl record and corresponding leaflet. This LP contains 400 Hz calibration tones as well. Quotes from the sleeve: "[...] Thousands of man-hours were spent listening, adjusting, optimizing—until harpsichords sound like harpsichords without mutilated transients, until bass viols sound like bass viols without harmonic distortion, until triangles sound lean and crisp without breathiness. The result is High-Com II, the world's finest two-band noise-reduction system. [...] High-Com II is the first audiophile noise-reduction system that achieves professional quality. [...] Listen especially for the dramatic reduction in surface noise on this High-Com II encoded record. There is no residual hiss; the ticks, pops, and crackles that mar conventional discs are absent. So is turntable rumble. The loud passages emerge with unprecedented clarity since they need not be recorded at so high and distortion-producing a level. [...] Between programs, there is utter silence. [...] We also suggest you listen closely for sounds of "breathing" and noise pumping. This common fault of noise-reduction systems has been eliminated in High-Com II. Listen also to High-Com II's remarkable ability to accurately preserve musical transients. They are neither muted nor exaggerated nor edgy as with other companders. This accuracy of reproduction—on all types of music, at all frequencies, and at all levels—is what distinguishes High-Com II from other noise-reduction systems. [...] Unlike simple companders, High-Com II is optimized differently for signals of different strength and different frequencies. Low-level signals are processed for maximum noise reduction, high-level ones for minimum distortion. This sophisticated technique assumes maximum dynamic range with minimum "breathing" and other audible side effects. [...] Sound of extraordinary dynamic range—a background free from surface noise, pops, clicks, rumble, and groove echo—the mightiest crescendo, free from distortion. Sound without breathing, pumping, or other ill side effects."
- Mielke, E.-J. (1977). Einfluß des Dolby-B-Verfahrens auf die Übertragungsqualität im UKW-Hörrundfunk. Rundfunktechnische Mitteilungen, Vol 21, pp 222 - 228.
- IRT (1981-12-30). IRT Technical Report 55/81. Prüfung eines modifizierten HIGH COM-Kompanders für den Einsatz bei der RF-Übertragung im UKW-Hörfunk.