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從標準看看我們對于AES3 的連接誤區

更新：2019-12-31 9:45:20　稿件：日升電子　調整大小:【大中小】

在音頻行業中相關標準的制定者基本上有幾大組織:

TIA ITU 主要基于通信需要做標準建立

AES 以專業音頻為主

EBU 以電視/電影配套的音頻標準為主

IEC 國際電工委員會

那談到數字音頻標準最最重要的標準應該就是 AES3了

這個AES3標準在我們連接行業當中的指導標準被寫在

AES3-4-2009(reaffirmed 2019)

用于數字音頻的AES標準—數字輸入輸出接口-

兩信道串行傳輸格式線性表示的數字音頻數據-第4部分:物理和電氣

AES standard for digital audio — Digitalinput-output interfacing —

Serial transmission format for two-channellinearly represented digital audio data
Part 4: Physical and electrical

(Multi-part revision of AES3-2003,incorporating Amendments 5 & 6)

關于連接被寫在附件C（規范性文件）平衡傳輸當中

下面我們就帶著大家瀏覽一些重點吧！

這張圖上面我們可以看到幾個亮點:
１．發送端必須接地而接收端是虛線可以選擇性的連接
２．傳輸線是對絞線
３．發送端線接收端都是110 Ω

NOTE The electrical parameters of the interface are based on those defined in ITU-T
recommendation V.11 which allow transmission of balanced-voltage digital signals over cables
up to a few hundred meters in length.

注釋提到了: 這樣的傳輸方式允許在長達幾百米的電纜上傳輸平衡電壓數字信號。
所以我們測試線纜AES3傳輸能力在低電容材料上曾經驗證過400M的傳輸
是沒有問題的,甚至中間有數個接頭

下面這是報告的一些部分

C.1.2 Equalisation
Equalization may be used at the receiver.
There shall be no equalization before transmission.
The frequency range used to qualify the interface electrical parameters is dependent on the maximum data rate
supported. The upper frequency is 128 times the maximum frame rate (about 6 MHz for 48 kHz).

C.1.2均衡器環節
最后的這一句是重點＂必須保證能適應48 kHz取樣頻率下6 MHz 的傳輸帶寬＂

C.1.3 Cable
The interconnecting cable shall be balanced with a nominal characteristic impedance of 110 Ω at frequencies
from 100 kHz to 128 times the maximum frame rate.
The cable shall be one of the following types:
• Shielded (screened) cable
• unshielded (unscreened) twisted pair (UTP) structured wiring (Category 5 or better, see
ISO/IEC 11801). see note 5.
• Shielded (screened) twisted pair (STP) structured wiring (see ISO/IEC 11801).
The same cable type shall be used throughout any single interface connection, including patch leads.

C.1.3電纜Cable 環節提到了:
互連電纜的額定阻抗為110Ω
可用頻率為100 kHz 至最大播放速率的128倍。也就是上面提到的6 MHz

電纜可以是以下類型之一:
•屏蔽(屏蔽)電纜
•非屏蔽(非屏蔽)雙絞線(UTP)結構布線(5類或以上,見ISO/IEC 11801)。見注5。
•屏蔽(屏蔽)雙絞線(STP)結構布線(見ISO/IEC 11801)。
在任何單一接口連接中,應使用相同類型的電纜,包括接插線。

那這邊需要解說一下為甚么可以用網線呢?
因為網線的特性阻抗是110Ω 又有很好的對絞密度
但是作為流動演出還有復雜案場為了降低被干擾與可靠性
使用專用的軟質有屏蔽 AES數字線就有其必要了

NOTE 1 Holding closer tolerances for the characteristic impedance of the cable, and for the
driving and terminating impedances, can increase the cable lengths for reliable transmission
and for higher data rates.
NOTE 2 Closer tolerances for the balance of the driving impedance, the terminating
impedance, and for the cable itself can reduce both electromagnetic susceptibility and
emissions.
NOTE 3 Using cable having lower loss at higher frequencies can improve the reliability of
transmission for greater distances and higher data rates.
NOTE 4 Care should be taken in design of the interface to provide adequate balance on the
twisted pair within the Category 5 cable. Using RJ45 connectors, conventionally wired, current
practice favours the use of pins 4 and 5 for AES3 signals (separating them from ATM signals
on the same cable, for example). Pins 3 and 6 are the preferred second pair. For full
protection, the interface may have to withstand power voltages specified to support network
equipment, and the use of transformers and blocking capacitors on the AES3 interface is
strongly recommended.
NOTE 5 UTP cable has been shown to offer transmission up to 400 metres overall
unequalised, or 800 metres equalised, at 48 kHz frame rate. (See AES preprint 3783)

注釋部分對于上面的條文做了更精確的說明:
對電纜如果能有極小的公差以保證特性阻抗跟發送接收端匹配
就可以增加電纜長度,以實現可靠傳輸和更高的數據速率。
選用損耗較低的電纜可以提高傳輸的可靠性,以便較高頻率下使用獲得更大的距離和更高的數據速率。

這兩者筆者深有所感

以3070100176 6.0mm/3070100098 4.8mm線纜來說

緊密的對絞特性阻抗約在90Ω 極低的電容可以傳輸200M無虞

但這個200M的中長期劣化程度是很低的!!

因為 176使用的是實心的XLPE形變量小

但若是選用的是發泡類型的線纜例如:3070101988

那初期傳輸距離與性能非常好

但是在中長期輾壓擠壓之后劣化就相對明顯

也就是上面講的＂公差＂明顯了實用距離會陡降

這也就是為何很多AES線纜為何在骨架填充上傾向選用PE條的原因
例如我司3070100180 就是為了給傳輸線對撐起空間
避免遭遇擠壓時導致大量的損壞

注4 則提醒用戶必須把網線的＂線對＂用起來用對!
標準中首選建議插腳4和5 次之是插腳3和6
標準中也對于設備端網口接口提出了一定的要求

至于注5 提到UTP電纜可以支持400米的無均衡器傳輸
這點寫得比較不嚴謹

忽略了:
１．一般網線是中空的對于對絞控制是缺省的可能導致對絞松開
２．網線的導體粗細多樣目前CAT5E UTP 市面上大多販賣的是
26AWG 這種使用0.4mm 銅絲的產品截面積僅得 0.12mm²對比早期的
24AWG 使用0.51mm 銅絲的產品截面積0.2mm²
這意味著截面積減少造成了電阻升高也就是插入損耗大
這就可能導致傳輸能力不如標準上所標稱的距離

（圖片來自于網絡）

C.2 Line driver characteristics
C.2.1 Output impedance
The line driver shall have a balanced output with an internal impedance of 110 Ù with a tolerance of 20 %, at
frequencies from 0,1 MHz to 128 times the maximum frame rate when measured at the output terminals.
C.2.2 Signal amplitude
The signal amplitude shall lie between 2 V and 7 V peak-to-peak, when measured across a 110-Ω resistor
connected to the output terminals, without any interconnecting cable present.
NOTE a typical value is 4 V ± 10 %.
C.3 Line receiver characteristics
C.3.2 Maximum input signals
The receiver shall correctly interpret the data when connected directly to a line driver working between the extreme voltage limits specified in C.2.2.
NOTE The AES3-1985 specification for line driver signal amplitude was 10 V peak to peak
maximum.
C.3.5 Common-mode rejection
There shall be no data errors introduced by the presence of a common-mode signal of up to 7 V peak at frequencies from DC to 20 kHz.

C.2線路驅動器特性
C.2.1輸出阻抗Output impedance 這邊指出了
內部阻抗為110Ω,容限為20%<<指出了允許的誤差值88~132Ω 這是標準所允許的寬容度

C.2.2信號幅度Signal amplitude
C.3.2最大輸入信號Maximum inputsignals
C.3.5共模抑制Common-moderejection
上述這三條我們綜合起來
可以知道:
線路驅動器信號幅度的規格若遵循舊標準的設備可能是最大值10 Vp-p
共模信號峰值還可能高達7 V
我們可以據此來確認信號線的絕緣耐受程度
不過若希望線纜能夠仿真數字通用那應該用更高的幻象電源48V來要求線纜的耐受質量
(還要額外加上安全系數)

C.3 Line receiver characteristics
C.3.1 Terminating impedance
The receiver shall present an essentially resistive impedance of 110 Ω with a tolerance of 20 % to the
interconnecting cable over the frequency band from 0,1 MHz to 128 times the maximum frame rate when measured across the input terminals. The application of more than one receiver to any one line might create transmission errors due to the resulting impedance mismatch.
C.3.3 Minimum input signals
The receiver shall correctly sense the data when a random input signal produces the eye diagram characterized
by a Vmin of 200 mV and Tmin of 0,5 UI. See figure C.2.

C.3線路接收器特性
C.3.1端接阻抗
內部阻抗為110Ω,容限為20%<<指出了允許的誤差值88~132Ω<<<再次確認標準所允許的寬容度
“The application of more than one receiver to anyone line might create transmission errors due to the resulting impedancemismatch.”
這句非常的關鍵
＂應用多個接收器可能會由于產生的阻抗失配而導致的傳輸誤差。＂
AES3 是點對點協議
因為數字傳輸講究的是特性阻抗的必須一路到底
一旦接收端并接意味著阻抗匹配立即不對襯

C.3.3最小輸入信號Minimum input signals
指出了200 mV的Vmin是衰減指標
但是要參照 0.5 UI的Tmin為特征的抖動指針

換言之2 V衰減到0.2V可以界定出一條線纜電阻的下限
但是0.5 UI的Tmin 則更嚴謹的界定了
纜線必須有極低的電容值
以免數字信號上升下降的充放電導致了抖動指標嚴重劣化

C.4 Connector
C.4.1 XLR connector
The standard connector for both outputs and inputs shall be the circular latching three-pin connector described in IEC 60268-12. Note: this type of connector is usually called XLR, or XLR-3.
An output connector fixed on an item of equipment shall use male pins with a female shell. The corresponding cable connector shall thus have female pins with a male shell.
An input connector fixed on an item of equipment shall use female pins with a male shell. The corresponding cable connector shall thus have male pins with a female shell. The pin usage shall be:
Pin 1 Cable shield or signal earth
Pin 2 Signal
Pin 3 Signal
NOTE The channel coding means that the relative polarity of pins 2 and 3 is not important.See Part 3, clause 6. However it is recommended that relative polarity is preserved for these signal paths. See AES26.

C.4.2 8-way modular connector
Where Category 5 structured cabling is used, the 8-way modular connector specified in IEC 60603-7
(sometimes called "RJ45") is required. While the interface is by definition insensitive to polarity, for the purposes of constructing adaptors, XLR Pin 2 should be connected to RJ45 Pin 5 (or other odd-numbered pin),XLR Pin 3 should be connected to RJ45 Pin 4 (or even-numbered pin), consistent with using one of the four twisted pairs.
Equipment manufacturers should clearly label digital audio inputs and outputs as such, including the terms digital audio input or digital audio output as appropriate.In such cases where panel space is limited and the function of the connector might be confused with an analog signal connector, the abbreviation DI or DO should be used to designate digital audio inputs and outputs,respectively.

C.4連接器Connector
C.4.1卡儂連接器XLR connector
指出了連接器標準為IEC 60268-12中所述的圓形鎖定三針連接器。
輸出連接器應使用帶陰殼的公座
輸入連接器應使用帶公殼的母座。

（圖片來自于網絡）

導體針腳的用途應為:
插腳1 電纜屏蔽或信號接地
引腳2 信號
引腳3 信號
請注意這邊信號沒有標示+/-與模擬并不一樣

腳2和3的相對極性并不重要
但是標準建議為這些信號路徑保留相對極性
這將可以確保線纜可以向下兼容
模擬信號時不會導致錯誤的連接

C.4.2 8針模塊化連接器8-way modularconnector
這一段提到了使用5類線纜
建議配合使用IEC 60603-7中規定的RJ45使用,
腳位如前面所述
但是設備制造商應明確標記數字音頻輸入和輸出,
至少應使用縮寫DI或DO來指定數字音頻輸入和輸出。
這個考慮應該是為了保持對絞的連續性
并且為了單根銅絲的線纜組裝困擾解套

3070100176/3070100098
200M AES3 測試通過
XLPE絕緣強度高流動演出推介
向下兼容 DMX-512 模擬音頻
極低電容<53PF/1M
0.1256mm2
3070100176 6.0mm鋁箔+80編編織屏蔽
3070100098 4.8mm鋁箔+80編編織屏蔽

3075100005
PE絕緣強度高垂直阻燃款
175M AES3 測試通過
向下兼容 DMX-512 模擬音頻
極低電容<31PF/1M
0.22mm2
鋁箔屏蔽
填充有抗拉尼龍絲
5.1mm

3070100180/3070100181
PE條骨架支撐
200M AES3 測試通過
*3070100180 200M+3070100188 200M AES3測試通過
向下兼容 DMX-512 模擬音頻
極低電容<31PF/1M
0.22mm2
3070100180 6.0mm繞包屏蔽
3070100181 6.0mm鋁箔+128編編織屏蔽