Tags

Working With Audio Signals

Working With Audio Signals

TV-Bay Magazine Scott Bosen
For most of the past century, working with audio signals was a very straightforward process. The audio information was converted to electrical signals in the form of a varying voltage between the two conductors in a pair (balanced) or between a conductor and the ground reference (unbalanced). The bandwidth, frequency response, distortion and noise requirements of audio circuits were all well-defined. Interconnecting audio equipment was a simple matter of matching impedance and levels, usually accomplished with simple circuits of passive devices.
 
The conversion to digital signal formats changed all of that. Beginning in 1985 with the publication of the first standards for what became known and AES/EBU digital audio, system designers were faced with an ever-growing number of complications. Digital audio consists of packets of data, each packet representing a voltage level derived by “sampling” the analog voltage of the input signal at a specific rate and converting that value to a digital value. At the decoder, these samples are sequentially converted back to their analog value, and the analog signal (or a reasonable facsimile thereof) is reconstructed. Because it is always preferable to avoid unnecessary decode-recode steps along the way, system designers needed to find ways of working with these digital signals in their native form. This is where the complications started to arise.
 
The first complication came with the need to switch between two signals or to mix two signals together. In the analog world, this was simple. A basic relay could do the switching, and a very simple circuit could do the mixing by adding the two signals together in a variable ratio. In the digital world, it became necessary to ensure first that the two signals were encoded at the same sample rate (several different rates are used), and then that they were synchronous with each other. Switching between two signals that are not locked to the same reference makes it impossible to switch on the boundary between the samples. The outcome is an invalid sample at the switch point, which results in a pop or click at the output device when the signal is decoded.
 
Even with timing problems taken care of, noise at the switch point remained a common issue. This was due to the fact that the digital audio signal is constructed of discrete samples. When a switch takes place, there is often an instantaneous difference in the values represented by the samples immediately preceding and immediately following the switch. When the signal is converted back to analog, this discontinuity cannot be tracked by the analog circuitry and the speaker that is presenting the audio. The result is noise at the switch point. This noise can be prevented through adjustment of the samples before and after the switch point so that the two signals are at similar levels when the switch takes place. This is often called a “soft” switch and is quite commonly used, but it is a long way from the relay described earlier.
 
After a few years, system designers finally had a full toolkit for implementing practical, reliable and cost-effective digital audio systems. Then the complications started all over again. The challenge this time was called “embedded audio.” When the Serial Digital Video signal format was standardized, there were provisions made for carrying “ancillary data” in the spaces where no active video was present. When this data came in the form of digital audio information, it was referred to as “embedded audio.” The advantages of combining audio and video signals into one transport layer are obvious. System complexity and cost can be reduced considerably by eliminating the need for audio cabling, patch panels, and distribution and monitoring equipment.
The price of this improvement is increased complexity in the video system, or reduced flexibility in handling the audio once it is multiplexed into the video stream. Consider the common problem of recorded material with audio tracks assigned to the wrong positions. In a separate audio system, it is easy to repatch the audio lines to the correct pattern and proceed.
 
Performing the same operation on material with embedded audio requires that the serial data be decoded, the audio data extracted and processed and then the resulting material re-encoded back to SDI for use in the system. The difference in cost is considerable and must be taken into account when designing a system that depends on embedded audio transport rather than traditional separate audio system design.

Tags: utah scientific | iss053 | audio signals | aes | ebu | Scott Bosen
Submitted by Scott Bosen Read this article in the tv-bay digital magazine
Article Copyright tv-bay limited. All trademarks recognised.
Reproduction of the content strictly prohibited without written consent.
What are these?
[center.text]
You can buy this place for your 120x60 banner

tv-bay for Broadcast Equipment Sales and Hire and now with Broadcast NEWS.
If you're in broadcast it's the place to be!

tv-bay.com is the home of new and used broadcast equipment sales and hire, new and used film equipment sales and hire, used video equipment and professional video and tv product sales and hire. For sale, wanted or for hire tv-bay has all the broadcast sales information and contacts that you will ever need along with industry jobs should you be looking for a change of direction or have a vacancy to fill. From Sony Broadcast products to used disc drives the site has it all. Simply subscribe to recieve the daily email containing updates and additions to broadcast equipment on the site. If you are looking for broadcast news or news about new pro video or broadcast gear then tv-bay is the right place for you.

To buy and sell or hire your new / used video equipment on tv-bay is easy, fast, and very successful. The used broadcast video equipment market needs a central location to advertise all the video equipment for sale. If you want to buy or hire broadcast ENG equipment from suppliers such as Sony Broadcast, Vinten, PAG, JVC, Panasonic, even Rycote or any other broadcast equipment manufacturer tv-bay is the place to start. Sony broadcast provides probably the widest range of cameras or camcorders, and video equipment to the broadcast industry and for this reason there is always a good supply of sony broadcast used video equipment available around the world. TV-BAY has provided the most comprehensive portal to all of the equipment from all of the dealers around the globe. Help and advice is on hand to choose the right VTR, camera, tripod. Although used broadcast video equipment can reduce your investment broadcast equipment is never cheap, with the massive choice of video equipment available on tv-bay you are sure to pay less. The next time you are purchasing or hiring used video equipment start your search at tv-bay.com. If you are looking for a Sony broadcast monitor there are over 300 units available. If you are looking for a tripod to support your broadcast camcorder there are over 250 items online. Serial converters, HDV camcorders, DVCAM camcorders, Digi Beta camera’s & VTR’s, DVC Pro equipment, used routers and switchers, waveform monitors and vectorscopes, even complete shooting kit including Sony DSR-PD170P, Vinten Pro 5, sennheiser K6/ME66, boom pole, rycote softie, case, and more....
Used video equipment whether it be broadcast & professional or consumer has never been so easy to find and if you require help then contact tv-bay - your internet broadcast dealer.
We have hundreds of reseller, dealer and hire company users with the biggest range of new and refurbished broadcast, film and video equipment from either dealer, reseller or private selle r. You will also find broadcast and media finance specialist Azule Finance, simply follow the links and complete a finance proposal online.

You can also find your new & used High Definition (HD) converters. Up & Down Conversion, HD-SDI to SD-SDI. Hi Def Cameras and Hi Def VTR’s from Sony Broadcast, JVC Professional, Panasonic Broadcast and Effect Technology to name but a few. If you are in the UK you can find Sony Broadcast equipment that has the Silver Support package included supplied by reputable broadcast dealers and broadcast resellers.

Visit our articles for quick search of equipment reviews and our unique broadcast industry knowledge base. For the lastestin broadcast show news and broadcast expo and events then go to www.broadcastshow.com and search the broadcast show coming soon.

sony quantel panasonic discreet grass valley avid ikegami tektronix pinnacle miranda apple vinten chryon snell and wilcox fujinon canon barco nicon kodak thompson nec phillips marconi gvg lightworks gml quantum avs jvc canford cartoni cintel cobalt denon diverse shure abekas ampex videotek hitachi electronic evertz fora formatt fostex ikegami inik jvc manfrotto libec nikon petrol pinnacle philips portabrace vinten elan yamaha probel rycote sachtler samsung mitsubishi dell ampex trilogy roland teac denon dolby apple arri swit tascam tekniche tektronix thomson aston beyer bts portaprompt pag kramer bestboy camrade contour idx murraypro VFX Bluescreen Chromakey sennheiser doremi shure acer lenovo laptop 360 systems abc accom aja agilent elan dk-technologies phabrix teletest broadcastshow quantel transvideo rycote telex mackie akai wohler marshall swit peli tsl panasonic zandar datavideo pro-bel avitel convex vistek freeway avid kramer snell and many many more......


PROMOTE YOUR COMPANY, PRODUCT OR EVENT WITH TV-BAY

wanted - for hire - for salemagazine - news - articles - jobs

tv-bay and tvbay are registered trademarks of tv-bay Limited:: Broadcast Equipment Sales
Copyright tv-bay limited 2004-2013 - all trademarks recognised