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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.
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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
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10dB
0dB
Dolby B
Dolby C
Dolby B
Dolby NR OFF
Dolby C
Dolby B
Dolby B
Dolby B
10dB
20dB
+10
0
10
20
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