請問一下 Aoublaster 的 SPDIF
我愛海...
借到了一張 Creative AWE32
看到上面有一個 spdif 不過 偷工 沒有焊
我後來自幾去買金手指來焊
請問 那個 spdif 輸出是騙人的 還是真的可以用的
and 我又去借了一台 低頻的 示波器 about 10hz-100khz 的
試了一下 看到了 一堆 鋸齒波
不過 確不是很清楚的
好像還帶有很多別的訊號
畫面 有點不是很清楚
不曉得只是真的 訊號 or 只是電腦內部的雜訊
因為 手上沒有 dac 不然就直接接看看 或許就知道答案了
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[0m [1;31m ◎ Origin: 中央松濤站□bbs.ee.ncu.edu.tw From: t202-31.dialup.seed.net.tw [0m
Fred Peng
1. AWE32 的 SPDIF Connector 之前的電路中還有一個
75ohm 交連變壓器做阻抗匹配用。這個交連變壓器
沒裝的話，訊號無法交連到輸出端。
2. SPDIF 訊號約為 1V, 1.5-2MHz,
你以 100KHz 的示波器看到的訊號只是雜訊而已。
3. 你沒有 DA Converter (AC3 Dolby Prologic Decoder 也可以)
要 SPDIF 做甚 ?
4. 為推廣知識，做一個專有名詞更正。
你買來焊在 AWE32 的小接頭，它不叫"金手指",
在 IBM 的維修手冊上這種接頭稱為 Pin Burg.
"金手指" 是指 ﹣﹣ 界面卡底端插在主機板插座的
公頭部份，其表面鍍金的排插 （公）。
AC-3
: > 因為 手上沒有 dac 不然就直接接看看 或許就知道答案了
目前只有AWE64 gold版的真正有SPDIF,
不過不能做AC-3輸出!
其他版本均被刪除了!
我愛海...
>==>發信人: Fred Peng <fr...@cis.com.tw>, 信區: Audiophile
>1. AWE32 的 SPDIF Connector 之前的電路中還有一個
> 75ohm 交連變壓器做阻抗匹配用。這個交連變壓器
> 沒裝的話，訊號無法交連到輸出端。
>2. SPDIF 訊號約為 1V, 1.5-2MHz,
> 你以 100KHz 的示波器看到的訊號只是雜訊而已。
天啊 這麼高 早知到借台好一點的來
我還以為 頂多是 44.1k 哎...
>3. 你沒有 DA Converter (AC3 Dolby Prologic Decoder 也可以)
> 要 SPDIF 做甚 ?
說真的 一開始只是覺得好玩....
>4. 為推廣知識，做一個專有名詞更正。
> 你買來焊在 AWE32 的小接頭，它不叫"金手指",
> 在 IBM 的維修手冊上這種接頭稱為 Pin Burg.
> "金手指" 是指 ﹣﹣ 界面卡底端插在主機板插座的
> 公頭部份，其表面鍍金的排插 （公）。
喔...謝謝你的指正...
另外請問那邊可以取得一些 spdif 的 技術文件資料..
謝謝
>我愛海... wrote:
>>
>> 借到了一張 Creative AWE32
>> 看到上面有一個 spdif 不過 偷工 沒有焊
>> 我後來自幾去買金手指來焊
>> 請問 那個 spdif 輸出是騙人的 還是真的可以用的
>>
>> and 我又去借了一台 低頻的 示波器 about 10hz-100khz 的
>>
>> 試了一下 看到了 一堆 鋸齒波
>> 不過 確不是很清楚的
>>
>> 好像還帶有很多別的訊號
>> 畫面 有點不是很清楚
>>
>> 不曉得只是真的 訊號 or 只是電腦內部的雜訊
>> 因為 手上沒有 dac 不然就直接接看看 或許就知道答案了
>>
>> --
--
[0m [1;33m ◎ Origin: 中央松濤站□bbs.ee.ncu.edu.tw From: ts1-65.showtower.com.tw [0m
Fred Peng
> 另外請問那邊可以取得一些 spdif 的 技術文件資料..
> 謝謝
>
SPDIF
The interface
The interface is a 'consumer' version of the AES/EBU-interface. The most
significant difference is the choice of connections. Originally, the
AES/EBU-interface uses the well known symmetrical connections with
impedancetransformers and an output impedance of 110 ohm. The
signal-level
of this interface is reasoably higher than in the consumer version
(3...10
volts). There are no real differences in the signals that are used and
the
format in which the data is encoded.
The signal on the digital output of, for instance, a CD-player is an
almost
perfect sine-wave, with an amplitude of 500 mVtt and a frequency of
almost
3 MHz.
For each sample, two 32-bit words are transmitted, which results in a
bit-rate of:
2.8224 Mbit/s (44.1 kHz samplingrate, CD, DAT)
3.072 Mbit/s (48 kHz sampling rate, DAT)
2.048 Mbit/s (32 kHz sampling rate, for satellite purposes)
The output impedance is standard 75 ohm, so ordinary coax can be used.
In
fact, the minimal input level is 200 mVtt, so there is no real need for
special quality cable.
The Coding Format
The digital signal is coded using the 'biphase-mark-code' (BMC), which
is a
kind of phase-modulation. In this system, two zero-crossings of the
signal
mean a logical 1 and one zero-crossing means a logical 0.
_ _ _ _ _ _ _ _ _ _ _ _
| | | | | | | | | | | | | | | | | | | | | | | |
clock 0 ___ _| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_
___ _______ ___ ___
| | | | | | | |
data 0 ___ _| |_______| |___| |_______| |___
signal 1 0 0 1 1 0 1 0 0 1 0
_ ___ _ _ ___ _ ___ _
Biphase | | | | | | | | | | | | | | | |
Mark 0 ___ | | | | | | | | | | | | | | | |
signal | | | | | | | | | | | | | | | |
_| |_| |___| |_| |_| |_| |___| |_| |___
cells 1 0 1 1 0 0 1 0 1 0 1 1 0 1 0 0 1 1 0 1 0 0
The frequency of the clock if twice the bitrate. Every bit of the
original
data is represented as two logical states, which, together, form a cell.
The length of a cel ('time-slot') is equal to the length of a databit.
The
logical level at the start of a bit is always inverted to the level at
the
end of the previous bit. The level at the end of a bit is equal (a 0
transmitted) or inverted (a 1 transmitted) to the start of that bit.
The first 4 bits of a 32-bit word (bits 0 through 3) form a preamble
which
takes care of synchronisation. This sync-pattern doesn't actually carry
any
data, but only equals four databits in length. It also doesn't use the
BMC,
so bit patterns which include more than two 0's or 1's in a row can
occur
(in fact, they always do).
There are 3 different sync-patterns, but they can appear in different
forms, depending on the last cell of the previous 32-bit word (parity):
Preamble cell-order cell-order
(last cell "0") (last cell "1")
----------------------------------------------
"B" 11101000 00010111
"M" 11100010 00011101
"W" 11100100 00011011
Preamble B: Marks a word containing data for channel A (left)
at the start of the data-block.
Preamble M: Marks a word with data for channel A that isn't
at the start of the data-block.
Preamble W: Marks a word containing data for channel B.
(right, for stereo). When using more than 2
channels, this could also be any other channel
(except for A).
Word and Block Formats
Every sample is transmitted as a 32-bit word (subframe). These bits are
used as follows:
bits meaning
----------------------------------------------------------
0-3 Preamble (see above; special structure)
4-7 Auxillary-audio-databits
8-27 Sample
(A 24-bit sample can be used (using bits 4-27).
A CD-player uses only 16 bits, so only bits
13 (LSB) to 27 (MSB) are used. Bits 4-12 are
set to 0).
28 Validity
(When this bit is set, the sample should not
be used by the receiver. A CD-player uses
the 'error-flag' to set this bit).
29 Subcode-data
30 Channel-status-information
31 Parity (bit 0-3 are not included)
The number of subframes that are used depends on the number of channels
that is transmitted. A CD-player uses Channels A and B (left/right) and
so
each frame contains two subframes. A block contains 192 frames and
starts
with a preamble "B":
"M" Ch.1 "W" Ch.2 "B" Ch.1 "W" Ch.2 "M" Ch.1 "W" Ch.2 "M" ...
| ||_ sub __|_ sub _|| |
| || || |
|__ Frame 191 ___||__ Frame 0 ___||__ Frame 1 ____|
|
block-start
Channelstatus and subcode information
In each block, 384 bits of channelstatus and subcode info are
transmitted.
The Channel-status bits are equal for both subframes, so actually only
192
useful bits are transmitted:
bit meaning
-------------------------------------------------------------
0-3 controlbits:
bit 0: is set during 4 channel transmission.
bit 1: 0 (reserved)
bit 2: copy-protection. Copying is allowed
when this bit is set.
bit 3: is set when pre-emphasis is used.
4-7 0 (reserved)
9-15 catagory-code:
0 = common 2-channel format
1 = 2-channel CD-format
(set by a CD-player when a subcode is
transmitted)
2 = 2-channel PCM-encoder-decoder format
others are not used
19-191 0 (reserved)
The subcode-bits can be used by the manufacturer at will. They are used
in
blocks of 1176 bits before which a sync-word of 16 "0"-bits is
transmitted
Electrical Interface
The electrical interface for S/PDIF signals can be either 75 ohm coaxial
cable or optical fiber. Usually consumer models use that coaxial cable
interface and semiprofessional/professional equipments use optical
interface. The electrical signal in the coaxial cable is about 500mVtt.
---------------------------------------------------------------------------
Conversion circuits
Here are some AES/EBU and S/PDIF circuit collected from various sources.
AES/EBU to S/PDIF signal level converter
AES out: 2-------330 ohm------------------- SPDIF in
|
3--- 91 ohm
| |
1---------|-----------------------
-
ground
SPDIF (this one is a bit tricky) to AES
_
+ 5 volt | \
SPDIF out: | +-| O-+
_ | |_/ |
diode ^ +-4,7k-+ _ | _ |
10 u (+) | | | | \ | | \ | 100 n
O-----+-||-+--------+--+--IC--+--+-| O-+-| O-+-120 r-||-+----+-- 2
| | | | | | |_/ |_/ | |
| +-||-+ 100n _ 2,2k | 1 k |
75r ^ diode | | IC | | AES
in
| | --- | --- |
--- --- | _ 220r
| | \ 100 n |
+--+---| O---+--120 r-||-+---+--- 3
Diode = 1N914 or 1N4148 | |_/ | |
| _ | 1 k +--- 1
| | \ | | |
IC = 74HC04 or CMOS 4049 +---| O---+ --- ---
|_/
我愛海...
另外 再請教一下
現在一般 cd md 的 數位輸出 同軸 or toslink
是用 那一種 通訊協定??!! (有點奇怪的講法 )
and S/PDIF 要接 特別的 dac or 一般的 dac 就可以解了呢??
謝謝
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[0m [1;34m ◎ Origin: 中央松濤站□bbs.ee.ncu.edu.tw From: t201-135.dialup.seed.net.tw [0m
Fred Peng
用 "通訊協定" 其實也沒錯。
MD 的 Digital In/Out 皆使用 S/PDIF,
與一般的 DA 相同，只是 MD 內部再經
Compression (in), and De-compresion (out).
若以 Digital out (Play Back), 接一般 DA Converter,
即可播放。
我愛海...
>MD 的 Digital In/Out 皆使用 S/PDIF,
>與一般的 DA 相同，只是 MD 內部再經
>Compression (in), and De-compresion (out).
>若以 Digital out (Play Back), 接一般 DA Converter,
>即可播放。
so 把 cd 的 digital output 跟 聲霸卡的 spdif (若是可用的話..)
接到 示波器上 應該會看到 "類似" 的波形...
我把 cd 接上去 看到的是 密密的方波 其實應該說是 一個帶狀的長方型
不過 接上 awe 32 卻是看到 類似鋸齒壯的 波形
so 那張 awe32 的 s/pdif 看來是廢囉...??
>我愛海... wrote:
>>
>> 另外 再請教一下
>>
>> 現在一般 cd md 的 數位輸出 同軸 or toslink
>>
>> 是用 那一種 通訊協定??!! (有點奇怪的講法 )
>>
>> and S/PDIF 要接 特別的 dac or 一般的 dac 就可以解了呢??
>>
>> 謝謝
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