354:
85:
326:"intervenes very far into recorder development and cannot simply be added to the existing electronics. It requires a fundamental redevelopment of the recording amplifier." Dolby, however, still hoped Dolby HX would gain acceptance "because it enables high fidelity quality with the future microcassette recorders with a tape speed of 2.4 cm/s". The latter promise did not materialize, either.
333:, it monitored the signal at its source but ignored the signal reaching the recording head. Variations in the gain or the frequency response of the recording chain disrupted the bias control curve. The adjustable pre-emphasis sub-circuitry was unnecessarily complex and expensive for the consumer industry. The Dolby B envelope detector, which by design was
448:. The earliest implementation, published by Nikolay Sukhov, was developed after Dolby HX Pro. It blended the elements of HX Pro (feedback control) and Dolby HX, varying the supply voltage to the common erase/bias generator, and added safeguards against transient overload, a common problem when recording from worn
925:, p. 269: "Eine technische Begründung für die spärliche Verbreitung des HX-Systems ist darin zu sehen, das es sehr weit in die Recorderentwicklung eingreift, und sich nicht einfach zu der vorhandenen Elektronik hinzufügen läßt. Dolby-HX erfordert eine grundlegende Neuentwicklung der Aufnahmeverstärker".
1012:
131:
The optimal bias level for each tape formulation is a compromise between maximum output levels, noise, distortion and frequency response. Nominal bias, corresponding to maximum sensitivity and/or maximum output at 10 kHz, is less desirable for mid-range frequencies. Over-biasing is better suited
472:
corresponds to a fivefold decrease in apparent noise floor at middle and treble frequencies. According to Sukhov, his system enables a practical signal-to-noise ratio of more than 80 dB, without noise reduction. Sukhov's designs were the subject of five patents issued between 1984 and 1989, all
396:
Dolby
Laboratories acquired the rights to the B&O patent and became its sole worldwide distributor. The new system was named Dolby HX Professional, which was later shortened to Dolby HX Pro. B&O retained the rights to use Dolby HX Pro in its products and, according to sources affiliated with
392:
According to B&O, its system assured only 3-5 dB gain in treble saturation, far less than Dolby HX. B&O's system did not rely on the Dolby IC and could be used with or without any noise reduction system. Negative feedback compensated for variations in gain and frequency response in the
293:
of the existing analog sources available to the consumer. Controlling erase and bias currents simultaneously could cause sudden drops in the effectiveness of erasure but this only happened during the loudest passages with much treble content, which was sufficiently higher than any residual unerased
191:
had very high maximum output levels and treble saturation levels but were prohibitively expensive for most home users. The early metal tapes had high absolute level of hiss and there were fears metal tape would quickly degrade but this did not happen. The second solution was developed independently
325:
publicly spoke against the adoption of Dolby HX. According to Studer, the shortcomings of Dolby HX greatly outweighed its intended benefits. A 1981 press release by Dolby for the German market indirectly blamed the system's failure on conservatism in the industry. According to Dolby, Dolby HX
220:
allows operation at higher input and output levels, albeit with a higher sensitivity (red curve). A well-designed adaptively biased circuit must gradually decrease bias current so the increase in sensitivity compensates for the saturation effects. The new, adaptive magnetization curve remains
459:
In line with the tastes of the home audio community, which still preferred reel-to-reel tapes to cassettes, the 1987 version was targeted at cassette decks and reel-to-reel decks. Adaptive biasing cannot substantially improve the performance of one-quarter-inch (0.64 cm) tape running at
208:
proposed the third alternative; adapting the bias current to the treble content of the source signal. The increase in high-frequency energy, which effectively overbiases the tape, would be compensated for with a reciprocal decrease in the output of the bias generator.
432:μPC1297. The new proposal was well received by the industry and by 1986, Dolby HX Pro became a standard feature in the upper segment of consumer cassette decks. In the following years, Dolby HX Pro migrated into the entry-level consumer segment, becoming the
320:
integrated Dolby HX into their cassette decks but no other manufacturers followed suit. Despite favorable reviews, Dolby HX was a marketing and an engineering failure. It was tested and rejected by audio engineers; while most did not disclose their findings,
1202:
1164:
1145:
1183:
1221:
159:
of 4.76 cm/s (1.87 in/s) and 9.53 cm/s (3.75 in/s) presents another challenge. Audible high-frequency components of the recorded signal act as biasing currents, resulting in excessive over-biasing that manifests itself in
341:. Bundling adaptive biasing with noise reduction at the hardware level was the worst of all shortcomings. The user could not turn off the Dolby B decoder and still use Dolby HX while recording. This discouraged the use of the more effective
88:
Simplified graphic explanation of the adaptive biasing principle. The shown magnetization curves (top) and bias control curve (bottom) are valid only at treble frequencies. The exact values of the breakpoints and slopes vary with
236:
on the control curve and the slope of its high-level segment depend on the frequency of the input signal, and the energy-loss mechanisms in the tape and the recording head. A practical adaptive-biasing system must employ
288:
of the two recording channels. Controlling both stereo channels with a single bias modulator was deemed acceptable due to the high degree of correlation between the left and right stereo signals, and the poor
212:
The effect of such compensation is evident from the typical magnetization curves. By default, when the source signal's treble energy is low, the recorder operates at a fixed optimal bias current I
460:
19.5 cm/s (7.5 in/s) or higher speeds in standard reel-to-reel recorders; its saturation envelope is suitably high for music signals. Adaptive biasing, however, permits a decrease in treble
357:
The complete Dolby HX circuitry built around the NEC μPC1297, made in 1989. The shown implementation is a rare example of a defeatable HX Pro, controlled with a user-accessible on/off switch.
937:, p. 269: "Dennoch stehen die Chancen für das HX-System nicht schlecht, weil es bei den kommenden (Mikro)-Cassettenrecordern mit 2,4 cm/s Bandgeschwindigkeit HiFi-Qualität ermöglicht.".
32:
in accordance with the level of high-frequency audio signals. With adaptive biasing, high levels of high-frequency audio signals cause a proportionate decrease in bias current using either
148:(dB) above the nominal value. This optimal setting improves linearity at mid-range frequencies but reduces dynamic range and causes a drop in high-frequency response, which is offset with
136:. As a side benefit, optimum bias improves the response to tape dropouts because stronger magnetic fields penetrate more deeply into the magnetic coating. Under-biasing causes excessive
373:
system. According to the patent, it monitored the high-frequency voltage at the "hot" end of the recording head, extracting the combined envelope of bias and treble audio signals. An
297:
Independent tests showed Dolby HX could raise the saturation levels at 10–12 kHz by 10 dB. According to Dolby, the improvement was most pronounced with high quality,
200:, and relied on limiting recording levels. The patented Tandberg Dyneq and Akai ADRS circuits electronically compressed the signal before it could overload the tape. In 1979,
164:
and early onset of saturation at high frequencies, especially when recording on low quality tapes with low saturation levels. In the 1970s, music typically published on
112:
response of the magnetic particles in the tape's magnetic coating. The frequency of the bias signal in consumer cassette decks is usually fixed at between 80 and 100
144:, and raises the susceptibility to dropouts, and is thus unwanted. In practice, tape is always slightly over biased; the optimal bias current is set at two or three
714:
244:
over the treble frequencies to attain the best performance of a specific recorder. The effect of changes in tape formulations is insignificant in the case of
298:
245:
188:
284:
that powers the common erase/bias generator, thus varying the bias current. Simultaneously, the same envelope modulates the level of high-frequency
184:
recordings of the late 1970s and early 1980s, however, often contain enough high-frequency information, or "hot" treble, to trigger tape overload.
393:
recording chain, eliminating the key shortcoming of Dolby HX. As a side benefit, the B&O system was also effective in reel-to-reel recorders.
501:
425:
44:
at the upper end of the audible spectrum and to a lesser extent, mid-range frequencies. The effect of adaptive biasing is most pronounced in
881:
128:
in the bias severely degrade audio fidelity. The level of the bias signal defines the slope and shape of the resulting magnetization curve.
1007:, Jensen, Jorgen Selmer, "Bias control method and apparatus for magnetic recording", published 1982-02-24, assigned to
216:(blue curve). Initial over-biasing assures good linearity but low sensitivity and low saturation levels. Reduced bias current value of I
377:
continuously compared the envelope with the preset reference level and adjusted the bias current being fed to the recording head via a
353:
412:
to adopt HX Pro for mass duplication. By
February 1983, according to Dolby, the company had two licensees in the home audio industry;
1303:
1279:
1255:
49:
280:. The HX circuit blends together the envelope signals of both stereo channels. The composite envelope modulates the output of a
40:
control system. Compared with the use of fixed bias current, adaptive biasing provides a higher maximum output level and higher
84:
248:. Different tapes require different optimal bias settings but the bias control curve can be identical for all ferric tapes.
1200:, Sukhov, Nikolaj Evgenyevich, "Device for magnetic recording with adaptive magnetizing", published 1990-01-30
285:
149:
1162:, Sukhov, Nikolaj Evgenyevich, "Method of magnetic recording with dynamic magnetizing", published 1988-12-30
1143:, Sukhov, Nikolaj Evgenyevich, "Magnetic recording apparatus with dynamic magnetizing", published 1988-12-30
1100:
976:
400:
At its launch, Dolby targeted HX Pro at professional markets. In August 1982, industrial tape duplicator manufacturer
1181:, Sukhov, Nikolaj Evgenyevich, "Device for magnetic recording with dynamic biasing", published 1989-12-23
1321:
1219:, Sukhov, Nikolaj Evgenyevich, "Device for magnetic recording with dynamic bias", published 1990-11-30
305:
161:
156:
177:
1371:
494:
378:
362:
330:
201:
33:
276:
of the mid-frequency and treble components of the source signals and uses it to modulate the gain of its
132:
for mid-range and low frequencies but it reduces tape sensitivity at higher frequencies and degrades the
725:
436:
standard equipment in consumer hi-fi, and was also integrated into professional reel-to-reel recorders.
421:
342:
338:
290:
133:
1041:
1008:
1216:
1197:
1178:
1159:
1140:
1004:
141:
461:
386:
308:
in June 1979. The system was offered to existing Dolby B licensees at no extra charge. In 1980–1981,
172:
did not contain much high-frequency energy and usually could not drive the tape into saturation. The
345:. The 30 dB gain in signal-to-noise ratio provided by dbx made Dolby HX virtually unnecessary.
453:
401:
117:
109:
97:
382:
269:
261:
205:
57:
1299:
1275:
1265:
1251:
366:
173:
165:
65:
37:
1081:
1059:
317:
273:
45:
738:
374:
241:
226:
301:
tape formulations. Poor-quality tapes did not significantly respond to adaptive biasing.
405:
281:
125:
29:
1365:
469:
417:
313:
73:
41:
17:
1289:
445:
409:
277:
187:
In the late 1970s, the recording industry proposed three solutions to the problem.
61:
225:. Owing to self-biasing effects, distortion at middle frequencies remains low and
60:
by 1979 and was rejected by the industry. The subsequent negative-feedback system
1293:
1269:
1245:
863:
465:
420:. The early adopters had to build Dolby HX Pro circuitry with general-purpose
137:
1344:
Sukhov, N. (1983). "Динамическое подмагничивание" [Dynamic biasing].
474:
449:
334:
238:
121:
105:
101:
93:
25:
361:
In 1980, an alternative implementation of adaptive biasing was patented by
370:
257:
193:
169:
53:
498:
265:
145:
369:(B&O). Unlike the feedforward Dolby HX, the B&O circuit was a
322:
52:
media. The first commercial implementation, the feedforward system
1045:
352:
181:
113:
83:
413:
309:
197:
221:
straight (green dotted line) to the maximum recording current I
429:
104:
along with the audio signal with the purpose of making more
1324:[Better treble recording with the Dolby HX System]
631:
629:
627:
578:
576:
574:
572:
404:
introduced HX Pro into its cassette-duplicator catalogue.
547:
545:
543:
541:
539:
537:
535:
533:
389:, and enabled easy adjustments of the normal bias level.
819:
817:
784:
782:
780:
493:
In practical applications the latter were replaced with
906:
904:
902:
900:
898:
815:
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677:
664:
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397:
Selmer, received a share of future licensing revenue.
1024:
1022:
953:
951:
949:
947:
945:
943:
116:. The quality of the bias signal is critical because
1322:"Bessere Höhenaufzeichnung mit dem Dolby-HX-System"
850:, p. 271: "Schlechte Bänder bleiben schlecht".
444:In 1983, adaptive biasing gained popularity in the
428:until the 1985 introduction of a dedicated IC, the
260:(for 'Headroom eXtension') designed by Gundry for
473:of which referenced the earlier Selmer patent as
999:
997:
995:
993:
381:. The monaural circuit was easily scalable for
329:The main drawback of Dolby HX was that, being a
24:is the technique of continuously varying the
8:
1353:Sukhov, N. (1987). "СДП-2" [SDP-2].
304:Dolby Laboratories launched Dolby HX at the
1121:"NEC IC Expands Bias in Audio Tape Heads".
864:"Engineers sound off to high frequencies"
635:
606:
594:
582:
563:
1075:
1073:
858:
856:
517:
486:
452:. The revised design, which used a new
1295:Small Signal Audio Design, 3rd edition
970:
968:
966:
910:
835:
823:
788:
751:
734:
723:
720:(Tape Recording and Buying Guide): 18.
668:
551:
524:
468:to 10 μs. A fivefold reduction of the
68:and marketed by Dolby, and became the
934:
922:
847:
708:
706:
704:
702:
700:
691:
618:
268:noise-reduction encoder. The Dolby B
7:
1028:
957:
155:Recording very low wavelengths at
14:
1123:Journal of Electronic Engineering
294:signals to make these inaudible.
497:, for example, built around the
337:, could not reliably track fast
232:The location of the breakpoint I
1332:(in German) (August): 269–271.
1:
1247:The Art of Sound Reproduction
264:operated as an add-on to the
96:is a strong, high-frequency,
977:"Tape guide: Doubling in NR"
1099:Dolby Laboratories (1983).
882:"Teac decks and test tapes"
456:IC, was published in 1987.
426:transconductance amplifiers
76:industry in the mid-1980s.
1388:
889:Modern Recording and Music
502:transconductance amplifier
80:Fixed and adaptive biasing
1066:. 1982-08-28. p. 31.
1060:"New Products / Dolby HX"
306:Consumer Electronics Show
162:dynamic range compression
72:standard of the consumer
1250:. Taylor & Francis.
1244:Watkinson, John (1998).
495:variable-gain amplifiers
152:in the recording chain.
1101:"Dolby HX Professional"
527:, p. 40, fig. 1-2.
379:resistive opto-isolator
18:magnetic tape recording
1274:. Newnes. p. 45.
1082:"Rx for tapes: HX Pro"
1044:. 2013. Archived from
1042:"Jørgen Selmer Jensen"
1009:Bang & Olufsen A/S
733:Cite journal requires
440:Subsequent development
422:operational amplifiers
358:
90:
1048:on 14 September 2013.
975:Burstein, H. (1983).
715:"The Dolby HX System"
713:Stark, Craig (1982).
464:from the standard 50
410:major recording label
356:
134:signal-to-noise ratio
110:inherently non-linear
87:
870:(21 Jun): 999. 1979.
387:multitrack recording
363:Jørgen Selmer Jensen
202:Kenneth James Gundry
189:Metal particle tapes
609:, pp. 312–313.
597:, pp. 310–312.
454:precision rectifier
343:dbx noise reduction
331:feedforward control
102:tape recording head
98:alternating current
1266:Hood, John Linslay
367:Bang & Olufsen
359:
291:channel separation
272:(IC) extracts the
270:integrated circuit
262:Dolby Laboratories
206:Dolby Laboratories
174:digitally mastered
168:or transmitted on
91:
66:Bang & Olufsen
58:Dolby Laboratories
1271:Audio Electronics
1086:Popular Mechanics
1080:Shea, T. (1986).
554:, pp. 39–40.
408:became the first
100:that is fed to a
64:was developed by
56:was developed by
38:negative feedback
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1088:(August): 34–35.
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142:modulation noise
46:compact cassette
36:or preferably a
22:adaptive biasing
1387:
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986:(February): 26.
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375:error amplifier
351:
299:high coercivity
254:
235:
227:intermodulation
224:
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215:
82:
12:
11:
5:
1385:
1383:
1375:
1374:
1372:Tape recording
1364:
1363:
1360:
1359:
1350:
1339:
1336:
1335:
1334:
1320:Dolby (1981).
1315:
1312:
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1262:
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1234:
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1113:
1110:(February): 7.
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1018:
989:
962:
939:
927:
915:
894:
891:(9): 31. 1980.
873:
852:
840:
828:
793:
756:
744:
735:|journal=
696:
694:, p. 269.
673:
640:
638:, p. 313.
636:Watkinson 1998
623:
621:, p. 270.
611:
607:Watkinson 1998
599:
595:Watkinson 1998
587:
585:, p. 312.
583:Watkinson 1998
568:
566:, p. 310.
564:Watkinson 1998
556:
529:
516:
515:
513:
510:
507:
506:
485:
484:
482:
479:
441:
438:
406:Warner Records
350:
347:
282:voltage source
253:
250:
233:
222:
217:
213:
178:direct-to-disc
126:direct current
81:
78:
48:and low-speed
30:recording head
13:
10:
9:
6:
4:
3:
2:
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1373:
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1323:
1318:
1317:
1313:
1307:
1305:9781000050448
1301:
1298:. CRC Press.
1297:
1296:
1291:
1290:Self, Douglas
1287:
1283:
1281:9780750643320
1277:
1273:
1272:
1267:
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1259:
1257:9780240515120
1253:
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1061:
1055:
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1047:
1043:
1037:
1034:
1031:, p. 45.
1030:
1025:
1023:
1019:
1010:
1006:
1000:
998:
996:
994:
990:
985:
978:
971:
969:
967:
963:
960:, p. 56.
959:
954:
952:
950:
948:
946:
944:
940:
936:
931:
928:
924:
919:
916:
913:, p. 40.
912:
907:
905:
903:
901:
899:
895:
890:
883:
877:
874:
869:
868:New Scientist
865:
859:
857:
853:
849:
844:
841:
838:, p. 39.
837:
832:
829:
826:, p. 38.
825:
820:
818:
816:
814:
812:
810:
808:
806:
804:
802:
800:
798:
794:
791:, p. 37.
790:
785:
783:
781:
779:
777:
775:
773:
771:
769:
767:
765:
763:
761:
757:
754:, p. 36.
753:
748:
745:
740:
727:
716:
709:
707:
705:
703:
701:
697:
693:
688:
686:
684:
682:
680:
678:
674:
671:, p. 40.
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462:equalization
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446:Soviet Union
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383:stereophonic
360:
349:Dolby HX Pro
328:
323:Willi Studer
303:
296:
286:pre-emphasis
278:side channel
255:
246:ferric tapes
231:
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154:
150:pre-emphasis
130:
92:
69:
62:Dolby HX Pro
50:reel-to-reel
26:bias current
21:
15:
1357:(1): 39–42.
1348:(5): 36–40.
1330:Funktechnik
1129:: 19. 1985.
1108:Audio (USA)
984:Audio (USA)
911:Sukhov 1983
836:Sukhov 1983
824:Sukhov 1983
789:Sukhov 1983
752:Sukhov 1983
669:Sukhov 1987
552:Sukhov 1987
525:Sukhov 1987
335:fairly slow
229:decreases.
157:tape speeds
34:feedforward
1338:In Russian
1238:In English
1233:References
1217:SU 1610487
1198:SU 1539830
1179:SU 1531134
1160:SU 1448357
1141:SU 1448356
1005:EP 0046410
935:Dolby 1981
923:Dolby 1981
848:Dolby 1981
692:Dolby 1981
619:Dolby 1981
450:LP records
339:transients
138:distortion
89:frequency.
1314:In German
1064:Billboard
1029:Hood 1999
958:Self 2020
481:Footnotes
475:prior art
239:heuristic
94:Tape bias
1366:Category
1292:(2020).
1268:(1999).
434:de facto
371:feedback
274:envelope
258:Dolby HX
252:Dolby HX
242:weighing
194:Tandberg
170:FM radio
146:decibels
70:de facto
54:Dolby HX
499:LM13700
266:Dolby B
1302:
1278:
1254:
1223:
1204:
1185:
1166:
1147:
1014:
218:b.red.
214:b.opt.
106:linear
1355:Радио
1346:Радио
1326:(PDF)
1104:(PDF)
980:(PDF)
885:(PDF)
718:(PDF)
512:Notes
182:disco
118:noise
28:to a
1300:ISBN
1276:ISBN
1252:ISBN
739:help
424:and
416:and
414:Aiwa
385:and
318:TEAC
316:and
310:Aiwa
234:af.o
223:af.1
198:Akai
196:and
180:and
140:and
124:and
108:the
504:).
430:NEC
365:of
204:of
192:by
122:hum
114:kHz
16:In
1368::
1328:.
1127:22
1125:.
1106:.
1084:.
1072:^
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1021:^
992:^
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730::
728:}}
724:{{
699:^
676:^
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626:^
571:^
532:^
477:.
466:μs
312:,
176:,
120:,
20:,
1308:.
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741:)
737:(
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