Identify the various streaming digital formats in terms of:
- number of
- sample rate and bit depth
- physical medium
- source or origin.
Chapter 6.3-6.5, Desktop
Audio Technology - Rumsey
Chapter 2, The Desktop Studio -
Data Formats and Packaging
Digital audio is arranged in logical methods for transmission
Transmitted data includes not only audio, but
information such as samplr rate, bit depth, user data and error detection.
Example: data layout for AES/EBU transmission
Data is assembled into sections known as frames and
Each frame carries the information for one sample
in two channels.
Each frame has two subframes. Each subframe defines a
sample value for each of two channels.
A Subframe has a length
of 32 bits:
Two Subframes are combined to make
a Frame which has a length of 64 bits:
- The preamble in the first subframe
= 1 (channel one) and the preamble for the second subframe = 2 (channel
192 frames make up a data block.
- When a preamble for a Frame
is 3, instead of 1, a new Channel Status Block begins.
channels status bits (30) are collected at the
receiver from the 192 successive frames to form two Channel Status Blocks
which consist of 192 bits each, organized into 24 bytes.
Status block data includes number of channels,
sample rate, wordlength.
User bits are configured similarly. They can convey different
data, such as names, adates, etc, according to system design.
TWO CHANNEL FORMATS
AES/EBU and S/PDIF use a similar method to encode data
but use different cables and connectors.
AES/EBU is used primarily on professional
S/PDIF was created for consumer products.
A few differences in conveyed data, but mostly interchangeable
AES/EBU (Audio Engineering Society/European Broadcast Union)
- Also known as AES-3 and AES 1985 (the year it was
- Most standard for professional digital audio
- Supports up to 24 bit/any sampling rate
- Self clocking but master clocking is possible
- Transmits 2 channels serially on single cable circuit
- Uses TTL voltage levels of +5V and 0V
- Specified to use 110-ohm balanced twisted wire pair
cables terminated with XLR connectors.
- Cables can run up to 100 meters (over 300 feet) without
need for EQ
- Mic cables are sometimes
used for short distances but not recommended due to it's variable impedance
rating (30 to 90 ohms) and "reflection" of data - digital cable
- Specification has been updated to allow use of 75-ohm coaxial cable with
BNC connectors. This allows for transmission on professional video cabling.
Data transmission speed is 64x the sampling rate (at
48 kHz, rate is 3.072 Mbps)
Transmision speed will vary with sampling rate
S/PDIF (Sony Philips Digital Interface Format)
- Meant for consumer products but may be seen on professional
- Supports up to 24 bit/48 kHz sampling rate
- Similar to AES/EBU(different voltage elvels, different
formatting of channel status bits - 192 status bits are organized as twelve
- Some of the bits within the Channel Status blocks are
used for SCMS(Serial Copy Management System), hidden flags to prevent consumer
machines from making digital copies of digital copies. See figure 13.7 on
page 452 of text.
There are two basic formats for S/PDIF:
- Uses 75 Ohm unbalanced coaxial cable with RCA connectors
- Cable lengths limited to 20 ft.
- TOSLINK - Uses plastic fiber optic cable and same
connectors as Lightpipe
- ST-type - Glass fiber can be used for longer lengths
ADAT Optical (ADI)
- Also known as "Lightpipe"
- Implemented on the Alesis ADAT MDM and digital devices
such as mixers, synths and effects devices.
- Supports of to 24 bit/48 kHz sampling rate
- Transmits 8 channels serially on fiber-optic cable
with proprietary connectors
- Distance limited to 33 ft., or up to 100 ft. with glass
- Data transmission at 48 kHz is 12 Mbps
- Self clocking - although some devices may require a
separate 9-pin sync cable to work
- Channels can be reassigned (digital patchbay functions)
- Do not try to connect ADAT optical on one device to
TOSLINK on another even though they use the same connectors.
TDIF (Tascam Digital Interface Format)
- Implemented on Tascam's family of DA-88 recorders and
other digital devices such as mixers.
- Supports of to 24 bit/multiple sampling rates
- Transmits 8 channels on multiwire, unbalanced cables
with 25-pin D-sub connectors
- A bi-directional interface: a single multipin cable
carries data in both directions
- Cable length limited to 5 meters
- Data transmission at 48 kHz sampling rate is 3 Mbps
- Intended for a master clock system, however self-clocking
achieved with LRCK if supported
Multichannel Audio Digital Interface (MADI)
- an extension of the AES3 format (AES/EBU) for multichannel
- supports up to 64 channels of 24 bit audio at 48 kHz,
or 32 channels at 96k
- Data transmission is asynchronous at 100 Mbps, regardless
of data being transferred
- Master clock required - must be applied to all transmitters
- transmits on a single 75-Ohm video coaxial cable
with BNC connectors, or fiber optic cable
- cable length can be up to 100 meters