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High Com

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This article is about the noise reduction system. For HIGHCOM, see Factions of Halo.

The High Com (also as HIGH COM, both written with a space) noise reduction system was developed by Telefunken, Germany, in the 1970s as a high quality high compression analogue compander for audio recordings.

High Com

Compander variants
Name telcom c4 High Com High-Com II High-Com III High Com FM
Medium magnetic tape magnetic tape magnetic tape,
vinyl disc[nb 1]		 magnetic tape FM radio broadcasting
Target market professional consumer consumer, semi-professional semi-professional consumer
Development start 1971/1972 1974 1978 1978 1979
Introduction 1975/1976 1978 1979 never (1981-1984)
Compander type linear fixed four-band (crossover: 215 Hz, 1.45 kHz, 4.8 kHz)[1][2] broad-band with pre-/deemphasis from 1.2 kHz to 8.6 kHz[1] fixed two-band (crossover: ? with pre-/deemphasis fixed three-band (crossover: ?, ?) broad-band with pre-/deemphasis
Compression 1.5:1:1.5 2:1:2 2:1:2 ? ?
Noise reduction 30 dB(A)[3] 15-20 dB(A)[4][5] 20-25 dB(A)[3] ? ?
Calibration / ident tone alternating 550/650 Hz, -0.13 dB[nb 2] originally 440 Hz, later 400 Hz, 0 dB, 200 nWb/m[6] 400 Hz, 0 dB, 200 nWb/m[3] N/A N/A
Leader tape 38 cm/s: red-white-black-white, 19 cm/s: blue-white-black-white[nb 3] ? ? N/A N/A

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 [de] four-band audio compander for professional use.[2] In April 1974, the resulting "RUSW-200" prototype first led to the development of a sliding two-band compander by Ernst F. Schröder of Telefunken Grundlagenlaboratorium, Hannover since July 1974.

However, the finally released High Com system, which was marketed by Telefunken since 1978, worked as a broadband 2:1:2 compander, achieving almost 15 dB of noise reduction for low[5] and up to 20 dB RMS A-weighted for higher frequencies,[4][5] while avoiding most of the acoustic problems observed with other high compression broadband companders such as EMT/NoiseBX, Burwen [it] or dbx.[4][7][8]

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[4][7][9][nb 4] / U401BG[4][nb 4] / U401BR,[5][4][10][11][nb 4] developed by Dietrich Höppner and Kurt Hintzmann of AEG-Telefunken Halbleiterwerk, Heilbronn.[4][12]

With minimal changes in the external circuitry the IC could also be used to emulate a mostly Dolby B-compatible compander as in the DNR (Dynamic Noise Reduction) system[5] for backward compatibility. Consequently, second-generation tape decks with High Com incorporated a DNR expander as well, whereas in some late-generation Telefunken, ASC and Universum tape decks this even worked during recording, but was left undocumented.

High-Com II and III

Nakamichi, one of the more than 25 licensees of the High Com system,[4] supported the development of a noise reduction system that could exceed the capabilities of the then-prevalent Dolby B-type system. However, it became apparent that a single-band compander without sliding-band technology, which was protected by Dolby patents, suffered too many audible artifacts. So High Com was further developed into the two-band High Com II and three-band High Com III 2:1:2 systems by Werner Scholz and Ernst F. Schröder of Telefunken assisted by Harron K. Appleman of Nakamichi in 1978/1979.[4][13][8] The two-band variant was eventually released exclusively as Nakamichi High-Com II Noise Reduction System later in 1979,[3][8][4][14][15][16] increasing the amount of noise reduction on analogue recordings and transmissions by as much as 25 dB A-weighted.[3]

High-Com II for vinyl

While originally designed for tape recordings, Nakamichi demonstrated the usage of High Com II on vinyl records as well in 1979.[8][nb 1]

In 1982 the same AEG-Telefunken team, who designed the High Com noise reduction system,[4] also developed the IC U2141B for the CBS Laboratories CX noise reduction system for vinyl records.[4]

High Com FM

Similar to the earlier Dolby FM[17] system in the USA, a High Com FM system was evaluated in Germany between July 1979 and December 1981 by IRT.[4] Based on the High Com broadband compander, it was field trialed between 1981 and 1984, but was never introduced commercially in FM broadcasting.[18][4][19][20][21][22][23][24][25]

Impact

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.[26] A low-cost implementation of the Telefunken High Com system as external compander box became available as Hobby-Com,[7] developed by Telefunken product development[4] and Thomsen-Elektronik[7] for WDR, distributed by vgs [de],[7] and promoted for do-it-yourself assembly in the popular TV series Hobbythek [de] format by Jean Pütz on 1980-02-07.[7][4]

More than one million High Com systems were sold between 1978 and 1982.[10][27] While implemented in dozens of European and Japanese consumer device models and acoustically much superior to other systems[8] such as Dolby B,[7][8][27] C,[27] dbx,[4][7] adres [ja][7] or Super D,[7] 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) in 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, 0 dB, 200 nWb/m[8] 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[4] and the Hannover development site was partially disbanded and refocused on digital technologies in 1983,[4] this also put the High Com development to an end. The latest tape decks to come with High Com were produced in 1986.

Tape decks with High Com

These tape decks are known to provide built-in support for High Com:

  • Akai GX-F37
  • ASC AS 3000
  • Rosita Audion D 700
  • Blaupunkt XC-240, XC-1400
  • ELIN Professional Micro Component Cassette Deck - Modell TC-97
  • Eumig FL-1000µP High Com[28][nb 5]
  • Grundig MCF 200, MCF 600, CF 5100, SCF 6200
  • Hitachi D-E75 DB/SL
  • Imperial TD 6100
  • Intel Professional Micro Component Cassette Deck - Modell TC-97
  • Körting [de] C 102, C 220
  • Revox B710 High Com[nb 6]
  • Neckermann [de] Palladium[29]
  • Nikko ND-500H
  • nippon TD-3003
  • Saba CD 278, CD 362
  • Schneider SL 7270 C
  • Sencor SD-6650
  • Siemens RC 333, RC 300
  • Studer A710 High Com[30][nb 6]
  • Telefunken TC 750,[4] TC 450, TC 450M,[29] TC 650M, STC 1 / CC 20, MC 1, MC 2, HC 800, HC 1500,[4] HC 3000, HC 750M, HC 730T, RC 100, RC 200, RC 300, various[31]
  • Tensai TFL-812
  • Uher CG 321, CG 344, CG 356, mini-hit
  • Quelle [de] Universum [de] Senator CT 2307, Senator CT 2307A, CT 2318 (for SYSTEM HIFI 7500 SL), Senator CT 2337
  • Wangine K-3M, WSK-120, WSK-220

Other devices can be used with an external High Com compander box.

See also

Notes

  1. ^ a b The Nakamichi High-Com II Noise Reduction System exists in two very similar but functionally slightly different versions: One variant has a special "Disk" mode setting to decode High-Com II encoded vinyl discs without having to pass the encoded signal through a connected tape deck first, whereas the other variant makes it slightly easier to activate the 400 Hz calibration tone and allows the Subsonic and MPX input filters to be activated at the same time. [1]
  2. ^ Some telcom c4 companders have a "Telcom Auto" setting which would automatically activate or bypass the telcom c4 system depending on if the telcom ident tone alternating between 550 Hz and 650 Hz every 500 ms was detected on the leader tape or not.
  3. ^ The colored leader tapes standardized (for example in "Technisches Pflichtenheft 3/9 der öffentlich-rechtlichen Rundfunkanstalten in der Bundesrepublik Deutschland") by IRT and the German public broadcasting industry indicating a record using Telefunken's telcom c4 system are defined as a sequence of 10 mm red, 20 mm white, 10 mm black and 5 mm white for 38 cm/s recordings, and 10 mm blue, 20 mm white, 10 mm black and 5 mm white for 19 cm/s. The colors must be facing the magnetic coating / tape head side of the tape. [2]
  4. ^ a b c The Telefunken TFK U401B integrated circuit was available in five revisions: TFK U401B chips with a yellow dot are equivalent to the U401BG. TFK U401BG chips with a blue dot are equivalent to the TFK U401BR. TFK U401BR chips with yellow dot as well as yellow and blue dots exist also. Yet another revision was planned to incorporate the changes to Telefunken's High Com system since about 1982 to no longer require external circuit modifications, but was apparently never released. These revisions were also used on Telefunken's own High Com modules, which were available in various assembly variants (for example BS 5335 / AT 349 355 003 or BS 5356 / AT 349 355 024) and also used in many third-party products. [3] [4] [5]
  5. ^ The Eumig FL-1000µP was alternatively available with either the Dolby NR (type B) or the Telefunken High Com noise reduction system and corresponding front plates.
  6. ^ a b The Studer A710 was alternatively available with either Telefunken High Com and DNR (PCB 1.710.483-00 + 1.710.493-00 each based on two TFK U401BR), or with Dolby B and C (PCB 1.710.489-00 + 1.710.492-00 each based on two HA 12038) noise reduction modules and front plates. Likewise, the very similar Revox B710 was alternatively available in High Com and Dolby B versions, but could be factory-upgraded to support both, Dolby B and C after the release of the Revox B710 Mk II model, which featured Dolby B and C only as well.

References

  1. ^ a b Peissig, Jürgen; ter Haseborg, Jan Remmer; Keiler, Florian; Zölzer, Udo (2004-10-05). "Digital Emulation of Analog Companding Algorithms for FM Radio Transmission" (PDF). Proceedings of the 7th International Conference on Digital Audio Effects (DAFx'04). Naples, Italy: 285–290. Archived from the original (PDF) on 2017-11-14. Retrieved 2017-11-14. {{cite journal}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  2. ^ a b Copeland, Peter (February 2009) [September 2008]. Redlich, Gert (ed.). "Manual of Analoque Sound Restoration Techniques". London, UK: The British Library Sound Archive (www.bl.uk). Chapter 9. Reciprocal noise reduction. Archived from the original on 2017-11-05. Retrieved 2017-11-05 – via Deutsches Hifi-Museum, Wiesbaden, Germany. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help) (NB. Copeland was strongly biased from a British perspective, but nevertheless very knowledgeable.)
  3. ^ a b c d e Nakamichi High-Com II Noise Reduction System - Owner's Manual - Bedienungsanleitung - Mode d'Emploi (in English, German, and French). 1980. 0D03897A, O-800820B. Retrieved 2017-11-10. {{cite book}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help) [6] [7] [8]
  4. ^ a b c d e f g h i j k l m n o p q r s t u Schröder, Ernst F. "The Story of HIGH COM". Archived from the original on 2016-04-16. Retrieved 2016-04-16. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  5. ^ a b c d e Schröder, Ernst F. (1980). "HIGH COM - The HIGH COM broadband compander utilizing the U401BR integrated circuit" (PDF). Semiconductor information. 80 (2). AEG-Telefunken. 2.80. Archived from the original (PDF) on 2016-04-16. Retrieved 2016-04-16. {{cite journal}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  6. ^ Heiliger, Jürgen (2011-08-18). "Telefunken CN 750 High Com" (in German). Archived from the original on 2017-12-08. Retrieved 2017-12-08. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  7. ^ a b c d e f g h i j Kamm, Dieter; Pütz, Jean (March 1980). Reis, Brigitte; Praßer, Gerhard (eds.). "High-Com, Hobby-Com - Für Hifi-Freunde: Musikgenuss ohne Rauschen" [High-Com, Hobby-Com - For Hi-Fi fans: Enjoying music without noise] (PDF). Hobbytip der Hobbythek (in German). 56. WDR. Archived from the original (PDF) on 2017-11-05. Retrieved 2017-11-05. {{cite journal}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  8. ^ a b c d e f g The Stillness of Dawn - High-Com II Demonstration Record (A limited edition not-for-sale High Com II encoded audiophile vinyl record and corresponding leaflet. This LP contains 400 Hz, 0 dB, 200 nWb/m calibration tones as well.). Nakamichi. 1979. NAK-100. 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.
  9. ^ "Datenblatt U401B High-Com" (in German). AEG-Telefunken. S8/V2.711/0279AI. {{cite journal}}: Cite journal requires |journal= (help)
  10. ^ a b Wiedenroth, Bernd (1982). "High-Com-Modifikationen" [High Com modifications]. Funkschau [de] (in German). 1982 (26): 69. Archived from the original on 2017-11-05. Retrieved 2017-11-05. {{cite journal}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  11. ^ Benn, Dietrich (January 1982). "(unknown)". stereoplay (in German) (1). {{cite journal}}: Cite uses generic title (help)
  12. ^ Höppner, Dietrich; Hintzmann, Kurt D.; Schröder, Ernst F. (1979), "Monolithisch integrierte NF-Kompander", Wissenschaftliche Berichte, 52 (1–2), AEG-TELEFUNKEN: 97–104
  13. ^ Schröder, Ernst F. (1979). "2-Band und 3-Band Kompander nach dem Kettenverstärkerprinzip (HIGH COM II und HIGH COM III)". Laborbericht (in German). Telefunken Fernseh- und Rundfunk GmbH.
  14. ^ "Nakamichi High-Com II". Stereo (in German). 1979 (11). November 1979.
  15. ^ "Nakamichi High-Com II". Audio (in German). 1979 (12). December 1979.
  16. ^ "Nakamichi High-Com II". KlangBild (in German). 1981 (06). June 1981.
  17. ^ Mielke, E.-Jürgen (1977). "Einfluß des Dolby-B-Verfahrens auf die Übertragungsqualität im UKW-Hörrundfunk" [Influence of Dolby B system on the quality of transmission in FM radio broadcasting]. Rundfunktechnische Mitteilungen (RTM) (in German). 21. Institut für Rundfunktechnik (IRT): 222–228.
  18. ^ "Prüfung eines modifizierten HIGH COM-Kompanders für den Einsatz bei der RF-Übertragung im UKW-Hörfunk" [Evaluation of a modified HIGH COM compander for usage in the RF transmission in FM radio broadcasting] (in German). Institut für Rundfunktechnik (IRT). 1981-12-30. Technical Report 55/81. {{cite journal}}: Cite journal requires |journal= (help)
  19. ^ "High-Com bei MW-Übertragung". Funkschau [de] (in German). 1982 (22): 61ff. 1982.
  20. ^ "High-Com im Rundfunk: Empfang verbessern". Funkschau [de] (in German). 1983 (17): 50ff. 1983.
  21. ^ Porges, Ivan; Schröder, Ernst F. (1983). "Ein kompatibles Kompandierungsverfahren für FM-Rundfunk und dessen schaltungstechnische Realisierung". Hörrundfunk. NTG Fachberichte #83 (in German) (6): 151–158.
  22. ^ "High-Com im Rundfunk: Plädoyer für den Feldversuch". Funkschau [de] (in German). 1983 (25): 44ff. 1983.
  23. ^ "High-Com FM; Großversuch". Funkschau [de] (in German). 1983 (26): 11ff. 1983.
  24. ^ "High-Com-FM-Decoder für High-Com-FM-Feldversuch". Funkschau [de] (in German). 1984 (3): 74ff. 1984.
  25. ^ "Rundfunktechnik: High-Com-FM-Feldversuch - Anmerkungen". Funkschau [de] (in German). 1984 (8): 69ff. 1984.
  26. ^ "Rotel High Com Noise Reduction System RN-1000 RN-500 - owner's manual" (PDF). p. 1-7. Archived from the original (PDF) on 2017-11-14. Retrieved 2017-11-14. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  27. ^ a b c Bruch, Walter (1983). "Von der Tonwalze zur Bildplatte (Teil II) - Entwicklung der Magnetbandtechnik". Funkschau [de]. 100 Jahre Ton- und Bildspeicherung (in German) (18, 19, 20, 21). Archived from the original on 2017-12-08. Retrieved 2017-12-08. {{cite journal}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  28. ^ Eumig FL1000µP Cassettendeck - Die Cassetten-Tonbandmaschine (Product flyer) (in German). 939.540/4. Archived from the original on 2017-11-13. Retrieved 2017-11-13. {{cite book}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help) [9]
  29. ^ a b "Frei Haus". Audio (in German). November 1980. Archived from the original on 2017-11-13. Retrieved 2017-11-13. {{cite journal}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
  30. ^ Studer A710 Professional Cassette Tape Recorder - Service-Anleitung - Service Instructions - Instructions de service (PDF) (in German, English, and French). 1984 [1980].
  31. ^ "Telefunken TC 750 - HiFi Stereo Recorder - 1979 - 1981". Archived from the original on 2017-11-05. Retrieved 2017-11-05. {{cite web}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help)

Further reading

  • Görne, Thomas (2006). Schmidt, Ulrich (ed.). Tontechnik [Audio technology] (in German) (1 ed.). Leipzig, Germany: Carl Hanser. ISBN 3-446-40198-9.
  • Wermuth, Jürgen (1975-11-22) [1975-11-19]. "Dynamik-Erweiterung durch neuartigen Studio-Kompander" [Dynamic expansion through novel studio compander] (in German). 10. Tonmeistertagung, Köln, Germany. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: location (link)
  • Wermuth, Jürgen; Temmer, Stephan F. (1975). "Dynamikerweiterung durch neuartigen Studio-Kompander" [Dynamic expansion through novel studio compander]. Funkschau [de] (in German). 1975 (18): 103–106 / 571ff. (NB. This article mixes up the Dolby curve.)
  • Schröder, Ernst F.; Wermuth, Jürgen (1976-10-05). "Ein neues Kompandersystem – Grundlagen und Einsatzmöglichkeiten" [A new compander system - Basics and applications]. Fernseh- und Kinotechnik (FKT) (Speech at the FKTG Tagung) (in German). 30 (12). Freiburg, Germany: 9–11.
  • Dickopp, Gerhard; Schröder, Ernst F. (1978). "Der Telefunken-Kompander" [The Telefunken compander]. Rundfunktechnische Mitteilungen (RTM) (in German). 22 (2): 17-28 / 63-74.
  • Dickopp, Gerhard; Schröder, Ernst F. (1978). "Meßverfahren für Kompander" [Measurement technologies for companders]. Funkschau [de] (in German). 50 (17): 29–32.
  • Schröder, Ernst F.; Wermuth, Jürgen (1978-07-13), Circuit system for the generation of a direct control voltage which is dependent on an alternating voltage, DE2830784, US4321482
  • Scholz, Werner (1978-12-23), Schaltung zur wahlweisen automatischen Dynamikkompression oder -expansion, DE2856045 [10] [11]
  • Schröder, Ernst F. (1979-05-12), Schaltung zur wahlweisen automatischen Dynamikkompression oder -expansion, DE2919280 [12] [13]
  • "HIGH COM". Audio Engineering. 1981 (3): 30–35. 1981.
  • "Hobbycom (High-Com): Testbericht". Funkschau [de] (in German). 1980 (13): 97ff. 1980.
  • "High-Com für Profis". Funkschau [de] (in German). 1980 (14): 8ff. 1980.
  • Wiedenroth, Bernd (1980). "High-Com - Überblick und Entwicklungsstand". Funkschau [de] (in German). 1980 (17): 67–71.
  • "Kompander-Einbau: Erfahrungen mit High-Com-Baustein". Funkschau [de] (in German). 1982 (16): 16ff. 1982.
  • "Rauschkiller: Dolby- und High-Com-Rauschminderung - Teil 1". Funkschau [de] (in German). 1983 (3): 76ff. 1983. Part 1., "Rauschkiller: Dolby- und High-Com-Rauschminderung - Teil 2". Funkschau [de] (in German). 1983 (4): 82ff. 1983. Part 2., "Rauschkiller: Dolby- und High-Com-Rauschminderung - Teil 3". Funkschau [de] (in German). 1983 (5): 80ff. 1983. Part 3.
  • Telefunken U401BR. Archived from the original on 2017-11-14. Retrieved 2017-11-14. {{cite book}}: Unknown parameter |dead-url= ignored (|url-status= suggested) (help) [14]
  • Schröder, Ernst F. (1981). "Kompatibilität von Konsumgeräte-Kompandern zur Geräuschunterdrückung" (Report) (in German). 1. Tonmeistertagung in München: 295–301. {{cite journal}}: Cite journal requires |journal= (help)CS1 maint: location (link)
  • Höppner, Dietrich; Schröder, Ernst F. (October 1980). "HIGH COM - ein Kompander zur breitbandigen Geräuschunterdrückung". Technische Rundschau (in German) (41).
  • Schröder, Ernst F. (Summer 1980). "Dynamikkompander - Stand und Ausblick" (in German). Nachrichtentechnisches Kolloqium im Fachbereich Elektrotechnik der Universität Duisburg. {{cite journal}}: Cite journal requires |journal= (help)
  • Schröder, Ernst F. (1980). "A New Integrated Audio Compansion System". Proceedings of the Forth European Conference on Electronics (Eurocon '80). Stuttgart, Germany: 612–614.
  • Dickopp, Gerhard; Schröder, Ernst F. (April 1979). "HIGH COM - Ein Kompander von Telefunken". Telefunken Firmenschrift (in German). Telefunken.
  • Schröder, Ernst F. (1989-07-07). Beitrag zur Analyse und zur Dimensionierung von Kompandern anhand einer einheitlichen Beschreibungsweise [Contribution to Analysis and Dimensioning of Companders by utilizing a Unified Description] (PDF) (PhD thesis) (in German) (PDF). Retrieved 2017-11-15. {{cite book}}: Check |archive-url= value (help); Unknown parameter |dead-url= ignored (|url-status= suggested) (help)
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