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什麼是預強化?

Date:2020/9/22 18:50:08 Hits:



-課程-Tes教學




Typically, prior to some process, such as transmission over cable, or recording to phonograph record or tape, the input frequency range most susceptible to noise is boosted.通常,在進行某些處理(例如,通過電纜傳輸或記錄到留聲機記錄或錄音帶)之前,會增加最容易受到噪聲影響的輸入頻率範圍。 This is referred to as "pre-emphasis" – before the process the signal will undergo.這被稱為“預加重”-在信號經過該處理之前。 Later, when the signal is received, or retrieved from recording, the reverse transformation is applied ("de-emphasis") so that the output accurately reproduces the original input.後來,當接收到信號或從記錄中獲取信號時,將應用反向變換(“去加重”),以便輸出準確地再現原始輸入。 Any noise added by transmission or record/playback, to the frequency range previously boosted, is now attenuated in the de-emphasis stage.現在,通過傳輸或記錄/播放添加到先前增強的頻率範圍的任何噪聲都將在去加重階段被衰減。
強調高頻信號分量,以使發射頻譜產生更均一的調製指數,因此在整個頻率範圍內具有更好的信噪比。調頻廣播和乙烯基(例如LP)中通常使用加重記錄。

在波形信號中
In processing electronic audio signals, pre-emphasis refers to a system process designed to increase (within a frequency band) the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.在處理電子音頻信號時,預加重是指一種系統過程,旨在相對於其他(通常為較低)頻率的幅度增加(在一個頻段內)某些(通常為較高)頻率的幅度,以改善總體通過最小化諸如衰減失真或記錄媒體在系統後續部分中的飽和之類現象的不利影響,實現信噪比。 The mirror operation is called de-emphasis, and the system as a whole is called emphasis.鏡像操作稱為去加重,整個系統稱為強調。

Pre-emphasis is achieved with a pre-emphasis network which is essentially a calibrated filter.預加重通過預加重網絡實現,該網絡本質上是一個經過校準的濾波器。 The frequency response is decided by special time constants.頻率響應由特殊的時間常數決定。 The cutoff frequency can be calculated from that value.可以從該值計算出截止頻率。

Pre-emphasis is commonly used in telecommunications, digital audio recording, record cutting, in FM broadcasting transmissions, and in displaying the spectrograms of speech signals.預加重通常用於電信,數字音頻記錄,記錄切割,FM廣播傳輸以及顯示語音信號的頻譜圖。 One example of this is the RIAA equalization curve on 33 rpm and 45 rpm vinyl records.一個例子是在XNUMX rpm和XNUMX rpm黑膠唱片上的RIAA均衡曲線。 Another is the Dolby noise-reduction system as used with magnetic tape.另一個是與磁帶一起使用的杜比降噪系統。

Pre-emphasis is employed in frequency modulation or phase modulation transmitters to equalize the modulating signal drive power in terms of deviation ratio.在頻率調製或相位調製發射機中採用預加重,以根據偏差比均衡調製信號驅動功率。 The receiver demodulation process includes a reciprocal network, called a de-emphasis network, to restore the original signal power distribution.接收機解調過程包括一個互逆網絡,稱為去加重網絡,以恢復原始信號功率分配。




去加重
In telecommunication, de-emphasis is the complement of pre-emphasis, in the antinoise system called emphasis.在電信中,去加重是預加重的補充,在稱為強調的抗噪系統中。 De-emphasis is a system process designed to decrease, (within a band of frequencies), the magnitude of some (usually higher) frequencies with respect to the magnitude of other (usually lower) frequencies in order to improve the overall signal-to-noise ratio by minimizing the adverse effects of such phenomena as attenuation distortion or saturation of recording media in subsequent parts of the system.去加重是一種系統過程,旨在(在一個頻帶內)相對於其他(通常為較低)頻率的幅度減小某些(通常為較高)頻率的幅度,以改善總體信噪比。通過最小化諸如衰減失真或記錄介質在系統後續部分中的飽和等現象的不利影響來降低噪聲比。特殊的時間常數決定了頻率響應曲線,從中可以計算出截止頻率。

紅皮書音頻

Although rarely used, there exists the capability for standardized emphasis in Red Book CD mastering.儘管很少使用,但在Red Book CD母帶製作中存在標準化強調的功能。 As CDs were intended to work on 14-bit audio, a specification for 'pre-emphasis' was included to compensate for quantization noise.由於CD旨在用於16位音頻,因此包含了“預加重”規範以補償量化噪聲。 After production spec was set at 10 bits, quantization noise became less of a concern, but emphasis remained an option through standards revisions.將生產規格設置為20位之後,就不再需要考慮量化噪聲了,但是通過標準修訂仍然可以選擇強調噪聲。 The pre-emphasis is described as a first-order filter with a gain of 50 dB (at 15 dB/decade) and time constants XNUMX μs and XNUMX μs.該預加重被描述為一階濾波器,其增益為XNUMX dB(以XNUMX dB /十倍頻程),時間常數為XNUMXμs和XNUMXμs。



Signal spectra for three pre-emphasis situations: (a) launched spectrum... |三種預加重情況的信號頻譜:(a)發射頻譜... | Download Scientific Diagram下載科學圖



在數字傳輸中
In high speed digital transmission, pre-emphasis is used to improve signal quality at the output of a data transmission.在高速數字傳輸中,預加重用於改善數據傳輸輸出處的信號質量。 In transmitting signals at high data rates, the transmission medium may introduce distortions, so pre-emphasis is used to distort the transmitted signal to correct for this distortion.在以高數據速率傳輸信號時,傳輸介質可能會引入失真,因此要使用預加重來使傳輸的信號失真以糾正這種失真。 When done properly this produces a received signal which more closely resembles the original or desired signal, allowing the use of higher frequencies or producing fewer bit errors.正確完成後,將產生一個與原始信號或所需信號更相似的接收信號,從而允許使用更高的頻率或產生更少的誤碼。

In serial data transmission, de-emphasis has a different meaning, which is to reduce the level of all bits except the first one after a transition.在串行數據傳輸中,去加重具有不同的含義,即降低轉換後除第一個比特外的所有比特的電平。 That causes the high frequency content due to the transition to be emphasized compared to the low frequency content which is de-emphasized.與不強調的低頻內容相比,這導致了由於過渡引起的高頻內容被強調。 This is a form of transmitter equalization;這是發射機均衡的一種形式。 it compensates for losses over the channel which are larger at higher frequencies.它補償了在較高頻率下更大的信道損耗。 Well known serial data standards such as PCI Express, SATA and SAS require transmitted signals to use de-emphasis.眾所周知的串行數據標準(例如PCI Express,SATA和SAS)要求傳輸的信號使用去加重功能。


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