digital audio interfaces - wordpress.com dan s/pdif blastica iwan b pratama hal 1 digital audio...

AES/EBU dan S/PDIF BLASTICA

Iwan B Pratama Hal 1

Digital Audio Interfaces A digital audio interface allows equipment such as audio mixers, recording devices or audio processors to be interconnected without degrading the signal quality. Unfortunately, there are different types of interface, most of which are incompatible, although in some instances you can wire a device with an AES/EBU interface to a device fitted with a S/PDIF socket. Most interfaces convey stereo (2-channel) audio over a single set of wires, although some also require a separate word clock (WC) circuit, which is often wired via a standard BNC connector. Common interfaces are described in the following sections. Sony/Philips Digital Interface (S/PDIF) S/PDIF conveys both channels of a stereo signal, usually via an RCA phono (PIN) connector, although some devices use a TOSLink fibre-optic connector. This interface is commonly used for domestic equipment, such as CD/DVD players, Digital Audio Tape (DAT) recorders, and MiniDisc (MD) machines, conveying 16, 20 or 24-bit samples at rates of up to 96 kHz.

• An S/PDIF circuit can be used to convey data instead of normal audio, including AC-3 data for Dolby Digital 5.1 surround sound, or DTS surround sound data.

Electrical Hardware S/PDIF in its ‘copper’ form uses a signal level of between 0.5 and 1 volts into a 75 Ω load over an unbalanced circuit. The similarity to a standard television signal makes it suitable for routing through equipment designed for video material. Since it’s meant to operate with 75 Ω cable it can also be used over long distances without equalisation, and in this regard is superior to the professional AES/EBU interface (see below).

• Some devices incorporate an output transformer for improved circuit isolation. • Although a standard RCA phono (PIN) connector is normally used for ‘copper

connections’, some professional devices and adaptors employ a BNC connector. • You may encounter equipment that has a fibre-optic connector, usually of the TOSLink

variety, using 1 mm plastic fibre-optic cable and visible red light. The high attenuation in this kind of fibre limits the maximum cable length to 10 metres or less. In addition, you may need an adaptor box to connect other S/PDIF or AES/EBU devices.

• PC-based hardware sometimes provides a digital output via a 2-pin header, also known as an HDR-2 interface. Although the data conforms to the S/PDIF standard, the 5 volt TTL signals are incompatible with S/PDIF.

Connecting to devices with an AES/EBU interface is possible, although the following points should be noted:-

1. A standard AES/EBU input accepts data with minimum eye height of 200 mV. This means that it should accept the S/PDIF minimum signal level of 500 mV peak-to-peak.

2. An S/PDIF input normally requires an attenuator to protect it from being damaged by the comparatively high level signal produced by an AES/EBU output.

3. The AES/EBU interface and S/PDIF convey different data flags. This means that you may find that a connection, although electrically satisfactory, simply refuses to work.

Further information about connecting different digital interfaces appears elsewhere in this article. Encoding S/PDIF is a domestic version of the AES/EBU interface (see below). The data is assembled in the same way, except for differences in the Channel Status bits (C-bits). It’s possible to interconnect AES/EBU and S/PDIF devices, either directly or via an adaptor box, the latter correcting differences in signal levels or modifying any offending C-bits.

• S/PDIF is sometimes called CD/DAT, IEC 958-11 or IEC 60958, although there are some differences in settings of C-bits between the S/PDIF and IEC 958-11 standards (see below).

• What appears to be an AES/EBU interface may actually be an SP/DIF interface with extra balancing circuitry, also known as the IEC 958-11 interface. Equipment with this



kind of interface may not work due to incorrect C-bits, such as bit 0 which is different for domestic and professional audio material.

• More about encoding can be found in the section concerning the AES/EBU Interface.

Channel Status Bits The C-bits for S/PDIF are organised as follows:- Bit(s) Function 0 0 - Consumer source of material 1 - Professional source of material 1 0 - Sample contains audio information 1 - Sample contains data • 2 0 - Copying prohibited (Copy Protect) 1 - Copying permitted (Copy Protect 'off') 3, 4 0, 0 - No audio emphasis 1, 0 - 50/15 µs emphasis 'on' 5 0 - Two-channel audio (default) 1 - Four-channel audio 6, 7 0, 0 - Mode 0 (bits 0-25 defined) Otherwise only bits 0-7 defined 8-15 Category Code of sender (Mode 0 only) 0, 0, 0, 0, 0, 0, 0, 0 - General (Gen) 1, 0, 0, 0, 0, 0, 0, 0 - Compact Disc (CD) 0, 1, 0, 0, 0, 0, 0, 0 - PCM Adaptor (PCM) 1, 1, 0, 0, 0, 0, 0, 0 - Digital Audio Tape (DAT) 1, 1, 0, 0, 0, 0, 0, 1 - DAT-P (Copying permitted)16-23 Reserved (Mode 0 only) 24, 25 Sampling Rate (Mode 0 only) 0, 0 - 44.1 kHz 0, 1 - 48 kHz 1, 1 - 32 kHz • Data samples can include MPEG3, AC3, DTS and other special IEC 61937 formats. Bits 0 and 1 have the same function in both S/PDIF and AES/EBU data. Bits 1 to 5 and 24 to 25 (in Mode 0) are copied from the source to destination. This means that the C-bits in recorded material are identical to those contained in the original data. The most important bits are usually set as follows:- Bit Usual State Notes 0 0 (off) Can prevent connection to professional equipment1 0 Indicates interface used for audio, not data 2 1 (on) Can be ‘0’ to prohibit copying (Copy Protect 'on')3 0 Set to ‘1’ if emphasis used whilst bits 4-8 are normally at 0. Assuming an SP/DIF input ignores bit 0, bit 2 is 1 (Copy Protect set to off) and bit 3 is 0 (No audio emphasis) then transfer from an AES/EBU source is possible. Bit 2 is usually at 1 in the AES/EBU interface, allowing copying via this kind of connection, even though copying the same material via an S/PDIF circuit may be prohibited.

• When copying between DAT machines the interface conveys indexing information, also known as start IDs. You should therefore turn off auto-indexing on the receiving machine.

Copy Protection (CP) Apart from the Copy Protect bit (see above), you may not be able to copy material via an S/PDIF when:-



1. Using an early DAT recorder Older DAT machines prohibit recording at 44.1 kHz to stop piracy of CDs, although recording at 48 kHz is possible. Such machines can sometimes be modified to record at all rates.

2. Using a DAT recorder fitted with SCMS Modern domestic DAT machines use the Serial Copy Management System (SCMS), which allows the recorder to make digital copies from some sources, such as an original CD, but prevents you making a second-generation DAT recording from such a copy. Hence a recording’s owner can copy material but endless duplication is prevented. Analogue copying is unaffected but ‘second generation’ copying via S/PDIF is again prohibited.

• SCMS is part of the S/PDIF standard and is not used for data transferred via an AES/EBU interface. Some professional machines with S/PDIF connections aren’t fitted with SCMS.

• Enabling Copy Protect whilst making an original recording prevents any digital copying.

SCMS works by recording two bits of data, collectively known as ID6, which are buried within the data recorded onto DAT. These bits control Copy Protection (CP), working as follows:- ID6 Effect 0 Unlimited copying is permitted 10 No copies (Copy Protect) 11 One copy, in subsequent copies ID6 set to 10The system works in conjunction with the S/PDIF Category Codes (see above). The following table shows how this operates in an SCMS-equipped DAT recorder:-

Source Cat Code ID6 1st Copy ID6 2nd Copy ID6 3rd Copy ID6CD CD - Yes 10 No - - - CD (CP) CD - No - - - - - General Gen - Yes 11 Yes 10 No - General (CP) Gen - Yes 11 Yes 10 No - DAT* Gen 00 Yes 11 Yes 10 No - DAT (PR)* Gen 11 Yes 11 Yes 10 No - DAT (CP)* Gen 10 Yes 11 Yes 10 No - DAT* DAT 00 Yes 00 Yes 00 Yes 00 DAT (PR)* DAT 11 No - - - - - DAT (CP)* DAT 10 No - - - - - SCMS DAT DAT 00 Yes 00 Yes 00 Yes 00 SCMS DAT (PR) DAT-P 11 Yes• 10 No - - - SCMS DAT (CP) DAT 10 No - - - - - * Pre-SCMS DAT machine: can produce DAT or General Category Codes (PR) Prerecorded material, including an analogue recording made on an SCMS DAT machine (CP) Copy-protected material • During copying, the Category Code is set to DAT-P and the Copy Protect flag is sent via the S/PDIF connection. The receiver always records from a DAT-P source but the Copy Protect flag identifies the material to prevent any further copies.

• Digital copying from an SCMS DAT machine to a pre-SCMS machine is only possible if ID6 is set to 00. This means that even ‘one-copy-allowed’ tapes will be blocked.

• Some professional machines allow you to manually set the condition of ID6.

AE

Iwa

AEThis(AEconnTheand convadapUnfstregettthe 16 oS/PDrequ

EleTheusinusedprob

As DigalsoFurt EncBi-pthatthat

Thisrece Sam

OrgDatsub-

ES/EBU

n B Pratam

ES/EBs interfac

ES/EBU) inector or,

e signal vocan ther

veyed by ptor box.

fortunatelyam, refusiting aroundata. or 20-bit sDIF, this uired for o• Some• An A

Digitaaccomcan be

ectrical He stereo dang a signad inside blems and• The p

end oplug olatter

mentioneital In

o on XLRsther inform

coding phase mart reversingt many of

s arrangemeiving dev

mpling Fr3

44

ganisatioa frames -frames, t

U dan S

ma

BU Intece, createdis really , when fittoltages usrefore damthe interf

y, some ing any m

nd this pro

samples ainterface

other purpe of the infAES/EBU al 5.1 surrmmodatinge transferr

Hardwarata is carral level ofsome equ

d for evenpermissiblof the circor socket is at a low

ed above, (DI) an

s. mation ab

rk encodig the wirethe transi

ment, knovice. The b

req (kHz)32 4.1 48

on of Daare sent o

the first c

S/PDIF

erface d by the a professted on a dsed by themage the faces are s

equipmenmaterial frooblem, ap

at 48 or 32e can’t noposes. formationcircuit ca

round soug eight chred to a pa

re ried on a f 5 to 10 uipment.

n longer wle cable leuit. Theseat one en

wer imped3-pole X

nd Digita

bout conne

ng is usedes in the bitions in th

own as sebit rate is

) Bit

ata out at theontaining

F

Audio Ensional ver

digital aude AES/EBlatter if a

so similar

nt responom the wrpart from

2 kHz areormally b

n in this sean conveyund, or DThannels oair of aud

balanced volts peakThe sign

wiring you ength can e normally

nd and a Bdance of 7XLR connal Out (

ecting diff

d, eliminabalanced che data m

elf-clockin determin

Rate (Mb2.0482.82243.072

e same ratg audio for

ngineeringrsion of

dio card, vBU interfaca direct cthat they

ds to therong categbuying a

e preferredbe used f

ection alsoy data inTS surrouof broadcadio tracks o

RS-422 ck-to-peak

nal can trcan instaalso be f

y take theBNC conn75 Ω, requnectors are(DO) to av

fferent dig

ating any circuit has

match the t

ng, allowsned by the

bit/s)

te as the r channel

g SocietyS/PDIF.

via a standce are mu

connectioncan some

e consumgory of eq

specialis

d, althougfor 24-bit

o applies tnstead of und soundast-qualityon a video

circuit witk, workingravel ovell equalisafurther exte form of ector at th

uiring the e used. Tvoid conf

gital interf

direct cus no effectiming of t

s the cloc sampling

sampling 1 (left),

y and EurIt’s conn

dard quartuch highern is madeetimes be

er/professquipment.st device t

gh 44.1 kHaudio, s

to S/PDIFaudio, su. Alternaty digitallyo tape rec

th alternag into a 1er 350 meation circtended by

f an inlinehe other. Tuse of ma

The connefusion wit

faces appe

rrent (DCt. This forthe bit clo

k signal tg frequenc

frequencthe secon

B

ropean Brnected uster-inch 3r then thoe. Howevconnecte

sional fla There isnthat can m

Hz can alince the

F. uch as ACtively, it cy compre

corder (VT

ating curr10 Ω loadetres of cuits or a r

y using trae device, fThe signaatching coections arth analogu

ears elsew

C) componrm of enc

ock, as sho

to be easicy, as show

y. Each fnd for cha

BLAS

roadcastining a 3-p-pole jack

ose used bver, the acd directly

ag within n’t any eamodify th

lso be usenecessary

C-3 data fcarry Dolbessed audTR).

rent (AC) d: a transfcable witrepeater dansformerfitted withal conveyeoaxial cabre often mue circuit

where in th

nent, whicoding alsown below

ily extractwn below

frame conannel 2 (ri

STICA

Hal 4

ng Unionpole XLRk. by S/PDIFctual data

y or via an

the datasy way of

he flags in

ed. Unlikey bits are

for Dolbyby E data,io, which

coupling,sformer isthout anydevice. rs at eachh an XLRed via the

ble. marked asts that are

his article.

ich meansso ensuresw:-

ted at thew.

ntains twoight). The

A

4

n R

F a n

a f n

e e

y , h

, s y

h R e

s e

s s

e

o e

AE

Iwa

inteblocstar SynAt tthe sin thHowpreaused The

SubTheBitsConBitsThequalbit (BitsThisbits Bit Indion eBit ThismayBit ThisusedBit UseTheof thThetotasubs200

ES/EBU

n B Pratam

rface alsocks. Each rt of block

nchronisthe beginnsample clhe above wever, theamble to d to identi

ese are illu

b-frame e sub-frams 0-3: Prentains cods 4-7: Aude four leaslity audio(LSB), Bis 8-27: Aus is encodare blank28: Validicates wheequipment29: User s can be uy use this 30: Chans containsd for S/PD31: Parit

ed to detece V, U, C anhese bits ae V and P bal capacitysequent b times a s

U dan S

ma

o carries block con

k.

sation ning of ealock, ensudiagram,

e preamblbe easily ify each c

ustrated be

Structume is madeeamble ding violatdio data st signific

o, where oit 0, is senudio dataded using ked to logidity Flag ether the t that has Data (U-b

used in anbit for he

nnel Status special DIF data. ty Bit (P-bct an odd nnd P bits cappears inbits are ‘ty of 192 bblocks neeecond.

S/PDIF

non-audionsists of 1

ach sub-fruring that d

there’s nle is madeidentified

channel an

elow:-

ure e up of the

tions, as d

cant bits aonly 16, 1nt first. Una

the standical 0 (off(V-bit) audio samseparate Abit) ny way. Had drum cus (C-bit) informatio

bit) number oconstitute n every ontied’ to thbits or 24edn’t be id

F

o data bi192 frame

rame theredevices atnormally e unique d, withound the star

e followin

described a

are used f8 or 20-b

nused bits

dard ‘twof).

mple is vaAES/EBU

However, acontrol, in

on (see b

f errors in4 bits in

ne of the 1he associa4 bytes, cdentical.

its, spreads, from 0

e’s a preat each enda transitioby breaki

ut confusinrt of a data

ng bits:-

above.

for 24-bit it coding are blank

’s comple

alid. It canU outputs

a DAT mn which ca

below). Th

n the sampevery sub

192 frameated audioan carry It may be

d over a to 191. H

amble, whd of the dion in the ing this rung it witha block, th

material is used fo

ked to logi

ement’ me

n also be for chann

achine wiase it’s be

he meanin

ple. b-frame; ines containe sample, winformati

e updated

number oHence the

hich is useigital link data for

ule. This h other dahe latter a

or Auxilior the maiical 0 (off

ethod with

used to ‘bnel 1 and c

ith an S/Pest avoided

ng of thes

n other wed in eachwhereas ton as reqat the in

B

of framesstart of fr

ed by the are syncheach pulscoding vi

ata. Differalways bei

ary (Aux)in data. Tf).

h the LSB

blank’ an channel 2.

PDIF connd.

se flags is

ords, 8 inh block. the U and quired. Noterface’s

BLAS

s and grourame 0 is

receiver hronised. Ase of the iolation arent preaming in cha

) data, sucThe least s

B sent firs

unwanted.

nection (se

s differen

n every fra

C bits, eaote that thframe rat

STICA

Hal 5

uped intocalled the

to extractAs shownbit clock.

allows thembles are

annel 1.

ch as lowignificant

st.Unused

d channel

ee below)

t to those

ame. Each

ach with ahe data inte; around

A

5

o e

t n . e e

w t

d

l

)

e

h

a n d



Channel Status Bits Equipment responds to C-bits in various ways. Some devices ignore certain data bits, allowing the audio data to be used, whilst others ‘lock out’ the material if the C-bits aren’t as expected. The C-bits in the AES/EBU interface operate as follows:- Bit(s) Function 0 0 - Consumer material (Not used with this interface) 1 - Professional source of material 1 0 - Sample contains audio information 1 - Sample contains pure data 2, 3, 4 0, 0, 0 - Audio Emphasis is not indicated (Receiving equipment should default to 'off'. Manual switching may be used) 1, 0, 0 - No audio emphasis 1, 1, 0 - 50/15 µs emphasis 'on' 1, 1, 1 - CCIT J17 emphasis 'on' 5 0 - Sampling frequency of the source is locked (default) 1 - Sampling frequency of source is unlocked 6, 7 0, 0 - Sampling frequency is not indicated (Default 48 kHz, receiver may get rate from AES/EBU data) 0, 1 - 48 kHz 1, 0 - 44.1 kHz 1, 1 - 32 kHz 8-15 Channel mode 12-15 User bits management 16-18 Use of aux sample bits 18-23 Source word length & encoding history 24-31 Multi-channel function description 32-47 Reserved 48-63 Channel origin data - alphanumeric 64-79 Channel destination data - alphanumeric 80-95 Local sample address code (32 bit binary) 96-111 Time of day code (32 bit binary) 112 - 119 Reliability flags 120 - 127 Cyclic redundancy check character The usual states for these bits are as follows:- Bit Usual State Notes 0 1 (on) Can prevent connection to domestic equipment 1 0 (off) Indicates interface used for audio, not data 2 1 Can be ‘0’ if bits 3 and 4 do not indicate state of emphasis3 0 Set to ‘1’ if emphasis used 4 0 Set to ‘1’ only when CCIT J17 emphasis used Bits 5-7 are often set to 0 whilst many devices simply ignore bits 8 to 127. When copying between DAT machines the interface doesn’t convey indexing information, also known as start IDs. Synchronisation Techniques In a complex studio system there can be problems with timing between the different digital devices. There are two basic methods of synchronising the equipment in such a system:- 1. Each device uses the word clock extracted from its AES/EBU input This is similar to the genlock principle used in a television studio. Although perfectly adequate for joining two devices the following puzzles can be encountered in a complex system:-



1. Which of two devices, interconnected in both directions, acts as the master clock? Note that some devices only become slaves to their input clock when switched into record mode.

2. Which device do you choose as a clock to drive other devices? 3. What happens if the device used as a master clock is switched off by mistake?

2. A master clock unit is used as the reference for the entire studio This requires a separate clock input on each device, preferably the same as an AES/EBU audio input. Unfortunately many pieces of equipment have a BNC word clock (WC) input instead, which requires a suitable conversion box that accepts a standard AES/EBU master clock.

• An AES/EBU master clock signal can also convey audio material or other AES/EBU data.

In a television studio the master clock should be locked to the video frame reference frequency, as well as to the local source of SMPTE timecode. Locking all three of these signals together ensures that sound, vision and timing information are all in step. Master clocks can have two grades of accuracy, as shown below:- Grade Accuracy in Parts per Million (ppm)1 ±1 2 ±10 Time Delays Signals are synchronous if the start of the preamble is within a set margin of the reference clock. Outputs should be within 1⁄20 of the sampling frequency and inputs within 1⁄4. It may be necessary to align the timing of clock inputs by adjustments within the equipment, but once set, it shouldn’t need to be changed again, since drift isn’t usually a problem.

• Most timing delays are caused by the effects of different lengths of cable. • Any jitter in the digital waveform can cause serious problems. This blurs the edges of the

data causing an increase in noise on the audio output. Unsynchronised Devices Some sources can’t be locked to the studio system, such as a CD player that provides a nominal output of 44.1 kHz but really operates at 44.098 kHz. Unfortunately, such devices often lack a clock input, whilst others run at the wrong rate, such as a CD player supplying a 44.1 kHz signal to a studio working at 48 kHz. There are three solutions to such problems:-

1. Use Analogue Circuits This can be a very cost-effective remedy, causing little degradation in quality.

2. Use a Sample Rate Convertor (SRC) An expensive option, often best avoided, except when converting between frequencies. The device adds or deletes samples as necessary, sometimes causing a small amount of distortion.

3. Use a Synchroniser The ideal solution where rates are nominally the same. A buffer within the device fills or empties over time, depending on which frequency is highest. The buffer is reset at its mid-point, when a 10 ms cross-fade is made between the current sample and the mid-point data.

An alternative type of synchroniser, known as a sample-slip synchroniser, works by dropping or repeating samples during silent periods. Both types of synchroniser perform the special operation once every 20 minutes for a 10 parts per million (ppm) error in sample rate. Another option is a short-term SRC, which uses interpolation to fix the problem at a faster rate. Other Interfacing Problems Most of the following problems can be solved, albeit with expensive hardware:-

1. Differences in bits per sample Even when things seem normal there may be problems with signal levels or distortion when connecting devices that use a different bit counts, such as a 16 bit ADC connected



to 20-bit device. It may be necessary to ‘re-dither’ the material or use a digital gain control box.

2. Clash of C-bits with S/PDIF See the section in this document that gives further details on S/PDIF.

3. Some C-bits giving incorrect flags One example of this is pre-emphasised audio data which actually lacks a no-emphasis flag.

4. Pre-emphasis Digital processing can introduce or remove emphasis, although not all devices can deal with emphasised data. CCIT J17 (NICAM 728) emphasis should only be used for broadcasting purposes.

5. DC offset This problem is usually caused by a badly aligned analogue-to-digital converter (ADC). If this happens, you may have to use a special device to apply digital high-pass filtering.

6. Asynchronous timecode In this situation the timecode contained in the AES/EBU data gets out of step with real time. A special device can be used to remove or replace the timecode in the data.

Sony Digital Interface (SDIF2) SDIF2 is rarely encountered, although it’s commonly employed in early analogue-to-digital converters, as used to adapt a video recorder for digital sound recording. Electrical Hardware The interface uses separate 75 Ω BNC connectors for left (L), right (R) and word clock (WC) signals. Each unbalanced circuit uses 5 volt transistor-transistor logic (TTL) levels into a 75 Ω load with direct current (DC) coupling. In a multi-track system several SDIF2 signals, in the form of balanced RS-422 circuits, can be wired via a single 50-way D connector. Encoding SDIF2 conveys audio in 16-bit to 20-bit form, complete with Emphasis and Copy Protect flags. Unfortunately, some equipment ignores these flags, requiring the use of manual switching. Each 32-bit slot, which occupies one cycle of the word clock, is made up as follows:- Bit(s) Function 0-20 Audio data 21-28 Control Information (word ‘1’ only, start of block)21-25 00 - Fixed value 26-27 00 - Emphasis ‘off’ 01 - 50/15 µs emphasis ‘on’ 28 0 - Copying permitted (Copy Protect ‘off’) 1 - Copying prohibited (Copy Protect ‘on’) 29 0 - Not start of block 1 - Start of block (block flag) User Information (in words ‘2’ to ‘256’ only) 30-32 Divided into two ‘bits’ of 1.5 bits length Bit A followed by bit B:- Bit A: 0 - Start of block 1 - Not start of block Bit B: 0 - Not start of block 1 - Start of block The most significant bit (MSB) of the audio data is sent first, irrespective of the audio word length. Two’s complement coding is used and unused bits are blanked to 0.

AE

Iwa

SynAlthhavcyclsam

MiThisdatabit c

YaThisits conn

Thiscloc

Both MuA msingthes A-DThismacopti

ES/EBU

n B Pratam

nchronishough a ce to connlic hiss, t

mpling freq• The W

opera• WC o• A sin

severa

itsubiss interfacea. A balanclock (BC)• The s

two c17-32

amahas interfacedigital sunection is

s connectck, wired

Pin(s) 1 2 3 4 5 6,7,Ca8

h circuits

ulti-chmulti-changle electrise interfac

DAT Ints propriechine, whical conne

U dan S

ma

sation lock is co

nect a sepatypically quency, thWC outpuate at 44.1 outputs arengle 75 Ωal devices

shi Inte, also knonced RS-4

C) connectstatus infochannels, 2.

a Steree first appuccessor s made via

tor conveyas follows

CiWoGrDaWoDa

ase ScrGr

use direc

hannelnnel interfical circuices are pro

terface tary inter

hich emploector conv

S/PDIF

oded into tarate wordat one or

he rising eut of older

kHz, done often fit

Ω terminats, usually

terfaceown as M

422 connetions are rormation similar to

eo Intepeared onthe DMP

a an 8-pol

ys two RSs:- rcuit ord Clockround ata ord Clockata reen

round/Enact current

l Interrface allowit. The moprietary d

rface prooys a stanveys up to

F

the data itd clock (Wr two Hzedge of whr devices,

n’t providetted to itemtor must bvia T-ada

e Melco, is siection is urequired. Ifor a Pro

o two aud

erfacen YamahaP7D, allole DIN plu

S-422 sign

k

k

able (DC) cou

facesws multi-

most commdesigns th

ovides conndard S-Vo eight ch

tself, it’s iWC) circu. The WChich is ali, such as e an accurms of eqube fitted

aptors, it s

imilar to Sused for eaIt operatesoDigi muldio channe

’s famousowing sevug, as show

nals, one

upling.

-track digmon systehat are inc

nnectionsVHS videohannels of

ignored byuit. If suchC circuit igned to ththe Sony rately phaipment that the endshould be

SDIF2, buach channs with 16-lti-track taels. The fi

s DMP7 Mveral mixwn below

for the a

gital audioms are de

compatible

to an Ao tape to f audio, sa

y some eqh a clock carries a

he start ofPCM161

ased referehat don’t hd of a cloconnected

ut doesn’t nel and sep-bit or 20-ape mach

first is for

MIDI-conxers to bew:-

audio data

o equipmescribed be with oth

Alesis Digrecord m

ampled at

B

quipment.isn’t prov

a square wf each data10 and 16ence and shave SDIFock circuid to the en

contain aparate wo

-bit audio.hine is carr tracks 1-

ntrolled me ‘cascad

a and the

ent to bebelow. Unher system

gital Audmulti-track

44.1 or 4

BLAS

. This meavided youwave signa slot.

630 systemshould noF2 connecit. If a clond of the

a clock sigord clock . rried over-16, the s

mixer, as wded’ toget

other for

e connectenfortunate

ms.

dio Tape k digital s8 kHz. Th

STICA

Hal 9

ans you’llu’ll hear anal at the

ms, whicht be used.

ctions. ock feedschain.

gnal in the(WC) and

r an extraecond for

well as onther. The

the word

ed over aely, some

(A-DAT)ound. Anhis means

A

9

l a e

h .

s

e d

a r

n e

d

a e

) n s



that two connectors are needed for an eight-track machine; one for the eight inputs and another for the outputs. In the same way, a 16-track machine requires a total of four A-DAT connectors. Digital audio cards that accommodate interface usually have a separate 9-pin synchronisation connector, which lets your computer control the transport mechanism of an associated A-DAT machine. Multi-channel Audio Digital Interface (MADI) MADI conveys multiple digital audio channels over a single circuit, each channel conforming to the AES/EBU standard. The 56 AES/EBU sub-frames are carried over a 75 Ω coaxial cable, up to 50 metres long, and fitted with BNC connectors. A separate synchronising clock cable is required. The interface operates at a fixed data rate of 125 Mbit/s, whatever sample rate is used, although the rate at the cable is reduced to 100 Mbit/s by using 4 to 5 bit encoding. This process breaks up each 32 bit sub-frame into 4-bit words, encoded as 5-bit words by means of a look-up table. This form of encoding reduces the direct current (DC) content of the signal. Synchronisation blocks are inserted at least once per frame. If the link isn’t used to it’s full capacity, extra synchronisation blocks are inserted to ‘fill’ the space on the bus. This is done using a device known as a Transparent Asynchronous Xmitter and Receiver Interface (TAXI). The AES/EBU sub-frames are as normal, except that the preamble bits 0-3 are replaced by:-

Bit Function 0 Frame Sync flag 1 Channel On/Off 2 A/B of stereo pair 3 Sync block

Tascam Digital Interface (TDIF) This interface is used for connecting Tascam multi-channel digital tape machines. It employs the same optical connector as the A-DAT interface, conveying the same number of channels, although it uses an entirely different data format. Yamaha 8 channel Interface This special interface consists of eight sets of RS-422 mono audio data and a clock signal, all wired via a 25-way D connector. The data itself can be in Yamaha, SDIF2 or Mitsubishi format. When used in Yamaha format this works in the same way as Yamaha’s stereo interface described above. However, if you feed stereo data into one channel of a multi-channel interface only the left-hand information is received. Also, there’s no direct method available for connecting two channels from a multi-channel device to an input that has a stereo interface. Digital Audio Connectors Most connectors for digital audio are in coaxial form, as used in radio frequency (RF) and video systems. They have a central signal pin, surrounded by a cylinder that provides screening. An appropriate coaxial cable should always be used. BNC This twist-and-lock coaxial connector is used for SDIF2 and various kinds of video interfaces. It’s also sometimes used for S/PDIF connections in professional systems. The 75 Ω type of connector is most common. Unfortunately, it’s rather too easy to plug this into a similar 50 Ω socket, which often results in jammed or damaged connectors.

AE

Iwa

PhoThiswellcan

RecversHowconv TOThisplasfibr XLAn the variAESconnare

Pi123

MuTheIt colockattacAn Aover DiVarThenecedevi AEThepeakanot

ES/EBU

n B Pratam

ono Plugs popular l as for vicause pro

cent connesions are owever, youventional

OSLink s form ofstic fibre-e limits th

LR Connexceptionfirst to m

ious typesS/EBU dinector is shown for

in Circu1 Scree2 Line 3 Retur

ultiway Ce shape of omes in 9king screwching conAmphenor a central

igital Ariations ine followinessary harice.

ES/EBU te signal lek whilst tther you c

U dan S

ma

g connecto

ideo and aoblems wi

ectors of often shodu should audio cab

f fibre-opoptic cab

he maximu

nector nally robumake thiss with digital signwired in r referenc

uit Cen Sc

Hrn C

Connectof a D conn9, 15, 25 ws, often innectors tol connectol projectio

Audio n the AES/ng informrdware. O

to S/PDIevel used bthat for Scan use a

S/PDIF

or, also knaudio conith socket

this type ddy. Thosensure thables often

tic connele and vium cable

ust connecs product.iffering nnal or a ‘XLR’ or

ce:-

Circuit creen

Hot Cold

ors nector, oft

and 35-win UNF foo Japaneseor is similon. The la

Interf/EBU inte

mation is Of course,

IF by the AE

S/PDIF is simple att

F

nown as annections is that are

are gold-se that comat digital

n aren’t su

ctor, whisible red length to

tor, also k. The ful

numbers omono anrder, as sh

CircuitScreenPrimarySecond

ten used fway form,orm, are ee hardwarlar to a D

atches are

face Soerface andsuitable

, these on

ES/EBU inormally

tenuator,

an RCA orin domestdesigned

-plated anme alreadaudio wir

uitable for

ch is oftelight. Th10 metres

known as l ‘Cannonof pins. Talogue sihown belo

t CirScr

y In pdary Out

for multi-t, as well

essential, are. connectoawkward

olutiond S/PDIF for an el

nly work

nterface iy in the raas shown

r PIN plugtic equipmfor the m

nd highly dy mouldering is alwuse at hig

en used foe high atts or less.

a Cannonn’ range The 3-polignal oveow. The d

rcuit reen phase t of phase

track audias high d

although m

or, but hasd but are a

ns can makelectronicsif the act

is meant tange of 0

n below.

g, is usedment. The

modern ‘sh

reliable, ed-on to a ways madegh frequen

or S/PDIFtenuation

n plug, sinof profes

le XLR ver a baladifferent t

e

io data, is density 15metric scr

s 14, 28, 3absolutely

e it difficus hobbyistual data

to be betw.5 to 1 vo

B

d for S/PD older ‘lo

hort’ style

although cable are

e of real cncies.

F circuitsintroduce

nce this cossional coversion canced circterminolo

similar to5 and 50-rews are u

6 or 50 plessential.

ult to connt who wis suitable

ween 5 andolt. To co

BLAS

DIF conneng’ varietof plug.

older ande surprisincoaxial ca

, employsed by this

ompany wonnectors an be usecuit. Normgies for th

o an elong-way versusually req

lug contac.

nect somewants to c

e for the

d 10 voltsonvert fro

STICA

Hal 11

ections, asty of plug

d cheaperngly good.able, since

s a 1 mms form of

was one ofcome in

ed for anmally thehe wiring

gated ‘D’.ions. Thequired for

cts spread

e devices.create thereceiving

s peak-to-om one to

A

1

s g

r . e

m f

f n n e g

. e r

d

. e g

-o

AE

Iwa

Thethat

A trsigntranThewithtran SP/Thisartic

Youadd

ES/EBU

n B Pratam

e followint employ e

ransformenal is propnsformer we less actih an XLRnsformer.

/DIF to As is slightcles on Us

u may haved to mak

U dan S

ma

ng circuit electronic

er can alsperly isolawith a winve may c

R socket

AES/EBtly trickiersenet, emp

ve noticedke the who

S/PDIF

is even sc balanced

so be addeated from nding ratioconsider aat one en

BU r, since yploys a lo

d that thisole thing c

F

simpler. Hd circuits

ed to the the grouno of 1:1, a ready-mnd and a

you’ll needogic chip c

s circuit dcomply ex

However, in place o

output ofnd circuit.of the kin

made attenBNC con

d to increcontaining

doesn’t havxactly wit

this variaof a standa

f such an This sho

nd commonuator, usunnector at

ase the sig six inver

ve an outth AES/EB

ation mayard transfo

attenuatould be in

only fittedually in tht the othe

ignal leverters, such

tput transfBU specif

B

y upset AEormer.

or to ensuthe form

d in compuhe form oer. This m

el. This cirh as the 74

former, alfications.

BLAS

ES/EBU

ure that thof a stand

uter netwoof an inlinmay also

rcuit, deri4HC04 or

lthough th

STICA

Hal 12

interfaces

he S/PDIFdard pulseork cards.ne deviceinclude a

ived from4049:-

his can be

A

2

s

F e

e a

m

e

AE

Iwa

TTAs alsogiviThepressimp

OncisolIf ywithtwo

whi

S/PUndintochip

ES/EBU

n B Pratam

L to S/Palready m

o known aing a signae kind of dsented by ple capac

ce again, ation in st

your devich an attenu inverters

lst the cir

PDIF to Tder some co a standarp:-

U dan S

ma

PDIF mentionedas an HDal of 5 vodevice use

an S/PDitor-linked

a transfotrict confoce doesn’tuator sim from a 74

rcuit below

TTL circumstard compu

S/PDIF

d, some PDR-2 interf

lts, whiched for the

DIF circuitd attenua

rmer can ormity to tt have eno

milar to tha4HC04 log

w uses the

ances you uter circuit

F

PC-based rface. Thih is incom TTL outpt. If it cantor, as sho

be addedthe S/PDIough currat shown agic chip:-

e 7HCU04 d

may want at TTL l

hardwareis signal i

mpatible wput may on deliver own here:

d to the oIF standarrent capacabove, wi

device fro

nt to convelevels. He

providesis at Tran

with S/PDIor may no12 mA i

:-

output of rd (see abocity you cth or with

om Philips

ert an S/PDere’s a sim

s a digitalnsistor TrIF circuitsot be capanto a 450

this circuove). can use alhout a tran

s and a cu

DIF signample solut

B

l output vransistor Ls. able of dri0 Ω load

uit so as

lmost anynsformer.

ustom tran

al into a fotion, again

BLAS

via a 2-piLogic (TT

ving the 7you can

to provid

y 5 volt drThis exam

nsformer.

orm that cn using th

STICA

Hal 13

in header,TL) level,

75 Ω loademploy a

de ground

river chipmple uses

can be fedhe 7HCU04

A

3

, ,

d a

d

p s

d 4

AE

Iwa

whithe

RefDigElekePanInteExcInteJanuThe©Ra

ES/EBU

n B Pratam

lst the sim‘traveller

ferencesgital Audioktor Electnorama w

erfacing, change 19erface anduary 1987

e Truth abay White

U dan S

ma

mple circu’ of the pr

o Problemtronics ma

website at Synchron

89 d Contro

7 out SCMS2004.

S/PDIF

uit shown reset norm

m Solvers, agazine, Jwww.epanisation

ol for Dig

S, Francis

F

below inmally set t

Francis RJul/Aug, 1anorama.nand Com

gital Reco

Rumsey,

ncludes ano around

Rumsey, S995

net mmunicat

orders, P

Studio So

n adjustme2.6 volts.

Studio Sou

tion, Fran

Phil Wilto

ound, Ma

ent for DC

und, July

ncis Rum

on, Broad

ay 1991

B

C offset, w

1991

msey, Di

dcast Sys

BLAS

with the v

igital Inf

stems Eng

STICA

Hal 14

voltage on

formation

gineering,

A

4

n

n

,

digital audio interfaces - wordpress.com dan s/pdif blastica iwan b pratama hal 1 digital audio...

Documents