Sherwood D-480 User Manual download pdf (Page 16)

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, CrO

2, 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.

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.

--0

--5

--10

--15

10 100 1k 10k

Dolby-HX-PRO ON

Dolby-HX-PRO OFF

Frequency (dB)

--20

250µW/M

Level (dB)

Characteristics of Dolby B-C type

Frequency (Hz)

Response (dB)

Noise Level (dB)

Frequency (Hz)

Noise Reduction Effect

+10

10dB

0dB

Dolby B

Dolby C

Dolby B

Dolby NR OFF

Dolby C

Dolby B

10dB

20dB

+10

20 50 100 200 500 1000 2000 5000 10000 20000

1 2 ... 11 12 13 14 15 16 17 18 19 20

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Sherwood D-480 User Manual Page 16

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