Network audio technologies

[kaushik]

With the advent of the new devices the networked audio it is becoming a appealing segment being researched for state- of- the- art modern day venues , households .

There are mainly two types of systems that are deployed :a fully standards-based network, or a proprietary network that may or may not use standards-based transport.


There are varying degrees to the of quality that can be achieved while transforming an analog signal into a digital stream and vice versa .
the system designer has to sort out the deployment based factors suchas scalability , economy,space constraints ,the type of venue and other factors .

After considering these one key factor that the drives the final choice of the system is 'latency'.This is imparted as a recult of the analog to digital conversions (A/D), digital to analog conversions (D/A), and digital signal processing (DSP).
For example, live sound applications, excessive letancy can cause listener fatigue and poorly reconstructed audio.

latency can be analysed function of the ratio between the direct sound and the sound that is delayed. In a large-scale sound system, where there is little to no direct sound, the delay does not become a problem until there is a noticeable delay between sight and sound.
It is said that when the direct sound is within 8 dB or so of the delayed signal, 20 milliseconds (ms) to 30 ms difference will be audible.
The same troubles the performing artist also .Small latencies on the order of 100 microseconds (µs) can cause phasing problems that can result in high frequency roll-off when they are added back into the mix with an un-delayed source.

With the advanced equipments this letancy can be minimized dramaticaly .Wheare as areas where cascading multiple digital devices along with anlog the letancy still poses a challenge for the system designer .

Two key factors in comparing digital audio networks are the sampling rate and the bit resolution that the network supports. The sampling rate is the ”rate” at which a digital device ”samples” the composite analog sound waveform over time.
Bit depth, or resolution, describes the potential accuracy of a particular piece of hardware or software that processes audio data. In general, the more bits that are available, the more accurate the resulting output from the data being processed.

A networked audio system has limitation on the number of channels that are available at any node . The limitation is because of bandwidth .
The bandwidth demand which is a factor of bit depth and sampling rate of the channels,better quality meaning more data to be transported , reducing the maximum number of channels which can be transported over a particular network’s architecture.

STANDERDIZED AUDIO NETWORKING:

These are based on standerdized protocols , specifications laid out by some bodies .
main advantage of these are cost effective solution for the end customer , as he does not need to pay for the custom solution .

The most common standard is AES3, more often called the AES/EBU (Audio Engineering Society/European Broadcasting Union) standard. AES3 uses a 110-ohm shielded twisted pair cable to send two channels up to 300 feet. The standard allows up to a 24-bit resolution with no maximum sample rate.

Another one if MADI (Multichannel Audio Digital Interface),features Serial digital transmission over coaxial cable or fibre-optic lines of 28, 56, or 64 channels is supported, with sampling rates of up to 96 kHz and resolution of up to 24 bits per channel.Transmission over a single 75-ohm coaxial cable has a limitation of 150 feet, but the use of fiber-optic cables can extend the length to two miles.The latest document for this is AES10-2003 specification.[ http://www.iis.ee.ethz.ch/~felber/Da...aes10-2003.pdf ]

Other standards are :
ADAT Optical (ADI) -old standard for Digital Audio Tape [DAT] transmission linkage,

Sony/Phillips Digital Interface (S/PDIF)-
It is an acronym for Sony Philips Digital Interface and is a CD "Red Book" standard digital audio transfer file format. A SPDIF interface can transport either stereo left-and-right channel information or multi-channel sound. It is typically found on audio and a/v equipment such as CD transports, Laser Disc players, DVD players, some digital satellite products and computer sound cards where it is implemented using an RCA connector.,

A common use for the S/PDIF interface is to carry compressed digital audio as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player to a home theater receiver that supports Dolby Digital or DTS surround sound.

Tascam Digital Interface (TDIF)-The TASCAM X-48 supports 96kHz at full channel count over 6 TDIF-1 connectors, using a post Version 2.0 specification.


PROPRITERY SYSTEMS :

The two most common proprietary systems, which use a standards-based transport, are CobraNet from Peak Audio, and EtherSound from Digigram. These systems transport audio data using standard IEEE 802.3 Ethernet protocols. Ethernet is used because it’s relatively inexpensive, reliable, and the technology has been, and will continue to be, upgraded by the computer industry.

Just a few years ago, 10baseT was the best thing going. Now, gigabit (100baseT) Ethernet has become viable and affordable. In order to integrate either of these technologies, a manufacturer must license CobraNet or EtherSound technologies from the developer in order to use them in their product(s).

CobraNet is capable of up to 64 bi-directional channels at a 48 kHz sample rate with a resolution of up to 20 bits per channel over a single 100Mbit link. This could mean that all you have to pull out to the front of house is a single CAT5 cable.
However the Cobranet has got some latency issues and hence finds use only in limited deployments .
However system on chip developments in the recent times has boosted low cost device design for Cobranet.E.g.Cirrus Logic Digital Audio Networking Processor, CS18101, Incorporates CobraNet Technology on a Chip.

EtherSound is different from CobraNet in that audio only flows in one direction. It offers 64 channels of 48 kHz sample rate at 24-bit resolution. The same off-the-shelf Ethernet switches and cabling can be used for distribution, but any audio that is added into the signal chain is only available to be peeled back off down stream of where it was added.


Resources:
http://www.Wikipedia.org
http://www.broadcastengineering.com/webcast/wheatstone/
http://www.boxesandarrows.com/view/l..._digital_audio


Network audio technology is here to play an important part in our lives , the newly fabricated components and awareness will play key role to make these technologies popular .