Sherwood D-480 operating instructions Principle of Dolby NR System

ENGLISH

DOLBY HX PROFESSIONAL HEAD ROOM EXTENSION(DOLBY HX PRO)

1.Dolby HX PRO is a professional recording bias system which are now available in some home cassette recorders that improving dynamic range and signal clarity for life-like sound quality.

When recording audio signals which contain high-frequency components, these components influence the bias and decrease the high recording frequencies. (If the amount of the bias is high, high frequencies are decreased,while the amount of the bias is low, high frequencies are increased, resulting in high distortion.)

The Dolby HX Pro system responds to high or low frequencies to regulate the oscilation of the bias level added to the recording head, thus providing a stable, effective bias to the audio signals being recorded.

When an audio signal contains a large number of high-frequency components, the bias is held to a low value and deterioration of high frequencies is avoided, where as for low frequencies, the bias is added at a fixed rate.

Bias is thus added at the optimum rate for both high and low frequencies.

2.The unit incorporates the Dolby HX Pro system which automatically adjusts the bias for nomal, CrO2, and metal tapes at both channels independently. Since the system is automatically engaged during the recording process only, the audiophile can enjoy the full benefits of any tape without worrying about proper adjustment of switches and encoding/decoding controls.

250∝W/M --0

	--5
(dB)
Level	--10

--15

--20

10

Dolby-HX-PRO ON

Dolby-HX-PRO OFF

100 1k 10k

Frequency (dB)

PRINCIPLE OF DOLBY NR SYSTEM

The Dolby NR system functions so that it automatically increases recording levels of medium and high frequencies when the recording signal level is lower than the specified level (encoding), and automatically reduces the output level to the normal level during playback (decoding). In this way, the tape hiss noise is remarkably reduced without affecting the sound quality. The Dolby NR system used in your cassette deck improves S/N ratio by about 5 dB at 1kHz and about 10 dB at 10 kHz B- type and by about 20 dB on the most frequency range in C-type. Furthemore C-type has the anti-saturation network which reduces the affects of high frequency saturation, improving high range frequency response.

			Characteristics of Dolby B-C type												Noise Reduction Effect
	+10	10dB									Dolby C		+10
																					Dolby NR OFF
												LevelNoise(dB)
Response(dB)	0		0dB			Dolby B							0
																						Dolby B
	20												20
		10dB							Dolby B
	10												10
		20dB							Dolby B
																						Dolby C
									Dolby B				20	50	100	200	500	1000	2000	5000		10000 20000
	20	50	100	200	500		1000	2000	5000	10000 20000
					Frequency (Hz)											Frequency (Hz)

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