Session - V

Mr. H.R. SinghEngineer-in-Chief, All India Radio, India

Digital Radio - New Experiences

Session Chairman

Speakers

Mr. Charles W KellyNautel Limited, Canada

Mr. Peter SengerChairman & Director, DRM, Deutsche Welle

Mr. David BirrerThomson Broadcast & Multimedia AG, France

Mr. Guy GampellAPT Broadcast, Ireland

Mr. H.R. SinghEngineer-in-Chief, All India Radio, India

thBorn on 7 May 1949, Mr. H.R. Singh obtained his Bachelors Degree in Electronics and Communication Engineering from University of Rourkee in 1970. After being selected through

thUPSC, he joined AIR, Bikaner on 12 July 1971 and later served at various AIR & Doordarshan stations as engineering head. Mr. Singh was promoted as Chief Engineer(East Zone), Kolkata in July 2001 and was in-charge of maintenance of Doordarshan and AIR installations of East Zone. He moved to Guwahati in October 2002 as Chief Engineer (North East Zone) and then to Delhi as Chief Engineer (North Zone), responsible for installation activities of AIR and Doordarshan in North Zone. He has served as Chief Engineer (Development), AIR Directorate and as Chief Engineer(Training),Staff Training Institute, Delhi before taking over

ndthe charge of Engineer-in-Chief, All India Radio with effect from 2 July 2007.

Mr. Singh has a wide experience in almost all the fields of broadcasting including station administration, projects and training. Mr. Singh has attended various workshops/ conferences on Executive Development, Human relations, Conflict Management, Modern trends in broadcasting and Computer Applications. His areas of interest are digitalization, IT applications and modernization of broadcast network.

Mr. Charles W KellyNautel Limited, Canada

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Abstract

In the move towards Digital Radio implentation on the AM and FM bands, broadcasters and regulators are dealing with issues of occupied bandwidth and the impact of DRM and HD Radio implementation on co-channel, as well as adjacent channel interference. Analysis, both theoretical as well as real world examples from around the world will be presented.

Digital Radio Implementation in AM & FM bands

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Bandwidth & Frequency Allocation Issues in International Digital Radio Am & Fm Broadcasting

As Digital Radio is implemented around the world, strength at the receiver to avoid interference from broadcasters face a key decision: Which digital radio the DRM signal into the analog receiver. system is right for my country? The answer to that

There are also proposals to implement a SSB AM question is complex, and encompasses many

signal and use the other half of the channel technical, regulatory, financial and political issues.

bandwidth (formerly occupied by the other This paper does not aim to solve the question, but

sideband) – but this is predicated on synchronous to examine one facet – the way existing band plans

detection of the AM signal, and in general, and allocation tables in the current AM and FM

shortwave receivers are much more likely to feature bands lend themselves to various technologies.

synchronous detectors than are AM radios. By limiting the scope of this paper to digital systems

HD Radio was developed to meet the unique needs which operate within the existing AM and FM

of the US broadcast market – and is based on the bands we do not discount DAB, DMB, DVB-T,

10kHz AM channel spacing found in North and DVB-H and ISDB-TSB which require additional

South America. In the US, the AM band is full of spectrum to be allocated. In fact, these technologies

stations, and there aren't a lot of open frequencies are not mutually exclusive to systems which operate

to put a stand alone digital signal. On the other within the existing AM and FM bands, and should a

hand, adjacent frequencies are not normally country implement one of the systems they will still

allocated within the same area, so HD Radio was be faced with the question of whether and how to

designed to keep the AM analog signal essentially digitize the stations within the AM and FM bands.

unchanged (just band limited to 5kHz audio response) and to utilize the spectrum beneath the AM IN-BAND SYSTEMS analog signal, plus on the two adjacent channels for There are two systems which are available for AM OFDM sidebands to pass the digital component. Digital Radio use, Digital Radio Mondiale (DRM)

and HD Radio™. While there are profound HD Radio fits the needs of broadcasters in the US, differences between them in bandwidth because it allows full simulcast of the legacy analog requirements, and flexibility, they are both OFDM signal as well as the new digital signal. Eventually, systems which use a number of sidebands to carry when digital receivers make up enough of the the digital information. receiver installed base, the analog signal may be shut

down, and the HD Radio signal will be reduced in DRM as it exists today, is designed as a bandwidth to 9.6kHz (+/- 4.8kHz). LW/MW/SW system, and has considerable

flexibility in how it may be configured to meet HD Radio reduces the effect of digital to analog on-various bandwidth, payload and robustness criteria. channel interference because the sidebands above The DRM Broadcasters' User Manual down- the carrier frequency are out of phase to those loadable from www.drm.org is a wealth of below the carrier frequency and are identical – thus information about the various options that DRM they cancel in the analog receiver. While this is makes possible. helpful for the on-channel signal, it does not affect

the interference to adjacent channels. In general implementation, however, DRM is normally installed with a 9 kHz bandwidth (carrier There is no question that HD Radio can create +/- 4.5 kHz), on a single channel, or 18 kHz significant interference to co-channel and adjacent bandwidth (carrier +/- 9 kHz) which utilizes one channel signals, and depending on the IF channel plus half of the two adjacents. There are bandwidth of the receiver, on the second adjacent options for using adjacent channels for an analog signals as well. This has the effect of reducing the AM broadcast, but this isn't in common use, as secondary coverage areas for a number of AM some tests have indicated that the analog signal stations – in some cases, dramatically. must be greater than 16dB above the DRM field

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bought three adjacent AM channels and installed an MARKET CONSIDERATIONS HD Radio AM station on the center frequency. He INFLUENCE DIGITAL STRATEGY broadcast the same programming on the analog and If the channel spacing in a country is 9 kHz, and digital transmissions, and used the analog channel there are free channels available for allocation, it is a to promote the purchase of HD Radio receivers, simple matter to implement DRM. Many European some of which are made in Indonesia. In this way, countries fall into this category, as reduced AM they provided higher quality audio programming to listenership has resulted in some AM stations being their loyal listenership, while having just one taken off air – and these "dark" facilities may easily transmitter, one antenna and paying a much less be re-purposed for DRM. expensive license fee from the government than an

In some cases, however, HD Radio has been FM station would have cost. implemented successfully for market reasons. In

Figure 1 shows how a standard HD Radio AM Surabaya, Indonesia in 2006, a religious broadcaster signal fits into a 9 kHz spacing band.

Where the AM band is fully utilized, and spare graphical analysis which presumes each station is channels are not available to construct new digital running HD Radio in Manila, the most populous only DRM channels, HD Radio is a possibility. An metropolitan area, and with the most crowded example is the Philippines, which like all of Asia, spectrum in the country. has AM channel steps of 9 kHz. Figure 2 is a

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As can be seen in Figure 2, the channel spacing on the same frequency has been presumably been within the Metro Manila area is 36 kHz between known for some time. With the HD sidebands stations and a guard band of 6 kHz exists between extending to +/- 15 kHz from carrier however, the AM HD sidebands. both of the first adjacent channels will be impacted,

and to a lesser extent, the second adjacent channels While Figure 2 is compelling, there is additional

will also be affected. Figure 3 is a graphical analysis analysis needed before any station is approved for

of the physical locations of first and second use with HD Radio AM. As these are existing

adjacent stations in the Philippines relative to one stations co-channel interference to other stations

50kW AM station.

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As can be seen from Figure 3, the nearest station on 50kW Manila station falls within the 2nd adjacent the first or second adjacent channels to 558 kHz in channel of DZMQ – nearly 200kM distant. Manila, is DZMQ, a 5kW station on 576 kHz in

A more serious problem exists with 1062 kHz – Dagupan City, nearly 200kM away from Manila.

figure 4 below: Calculating the power in each of the AM HD Radio sets of sidebands, approximately 375 watts from the

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In Figure 4, we see that there is a 1st adjacent DZEC in the Lucena area could be affected. It is station, DZEL 5kW, in Lucena on 1053 kHz. This important to understand that the digital sidebands station, only 100kM distant from Manila, would above the carrier and the mirror image ones below receive nearly 1,130 watts from the HD Radio the carrier carry the exact same information – thus, sidebands of 1062 kHz. It is likely that some if interference garbles the ones below the carrier, secondary coverage areas of DZEL would be the receiver can fully demodulate the program affected, and conversely, HD Radio coverage of audio – with reduced robustness.

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In adaptation of digital radio in these analog and digital signals are on a single FM circumstances, there are likely to be compromises to channel . DRM+/DRM120, cur rently in secondary coverage areas, but the tradeoff is that development, are digital only options, with the within the primary service areas, the broadcaster is OFDM carriers occupying 96 or 100 kHz of FM able to deliver dramatically improved audio spectrum. FMeXtra utilizes OFDM carriers added performance, as well as text data. to the composite baseband of a conventional FM

analog signal – and thus the bandwidth of the FM FM In-Band Systems signal does not appreciably change. Interestingly, There are three Digital In-Band systems – and they FMeXtra may be operated on an existing FM HD are all dramatically different. HD Radio works a lot Radio station – thus increasing the possible total like the AM HD Radio system, with OFDM carriers digital payload. on either side of the analog FM carrier, so both the

At this writing, HD Radio is currently on the air in compatible with all existing Seoul stations. In over two thousand stations, FMeXtra is on the air at addition, it can be seen that many DRM+ channels around 100 stations, and DRM+ is in testing stage at could also be fit into the band. several stations.

The FM spectrum in Taipei, Taiwan, is depicted in Figure 5 is a graphical depiction of the FM band in Figure 6 below. Between 88 and 89 MHz, there are Seoul, Korea – showing that FM HD Radio is four educational FM stations which are spaced by

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only 200 kHz. As can be seen, the HD Radio Note that in HD Radio FM, the sidebands above sidebands are on top of each other, and it is likely the analog carrier and the ones below the carrier are that poor coverage would result, with HD Radio carrying the same information, while there may be reception possible only where one station has a interference in one set of sideband – it may be significantly higher field strength that the adjacent possible for the receiver to properly decode the HD channels. signal on just the clear set of sidebands, albeit with

less robustness. Between some of the stations, such as the ones at 89.3 MHz and 87.7 MHz, there is only 400 kHz In some cities, stations on the FM band are spaced separation. Theoretically, this will work, however too closely for either HD Radio or DRM+. For the reception of one of the sidebands may be instance, the metropolitan Istanbul, Turkey market impacted if the immediately adjacent sideband is has FM stations virtually every 200 kHz from 87.5 significantly higher in received strength. This to 108 MHz. In this situation, it may be that the only condition is not unlike blanketing interference in workable in-band digital system would be FMeXtra. analog FM.

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ABOUT THE SPEAKER

Charles W. Kelly, Jr. is a 34 year veteran of Radio, starting as a DJ at his college station at the University of Illinois. He has held positions as News Director, Program Director and Chief Engineer at stations in Illinois and Colorado. He was educated at the University of Illinois, Illinois State University, Parkland College, and Fort Lewis College. Prior to joining Nautel in October of 2006, Mr. Kelly served as Director of International Sales for Broadcast Electronics for 18 years and as Sales Manager of ITC/3M for 7 years.

Mr. Kelly is a two term Past President of the Society of Broadcast Engineers (SBE), a professional society with over 5000 members in over 30 countries. He currently serves the on the SBE International Committee.

Mr. Tim Hardy, Nautel Limited, Halifax, NS Summary Canada The selection of a digital radio standard

encompasses much more than simply the technical Mr. Glen English, Pacific Media Technologies, capabilities of the systems. An examination of Cooma NSW Australia frequency usage, both within the market, as well as

HD Radio is a registered trademark of iBiquity far field, can reveal how a successful transition can Digital Corporation. be made with minimal interference.

Acknowledgements

The author is indebted to:

Mr. Peter SengerChairman & Director, DRM, Deutsche Welle

V-11

Abstract

The DRM-System up to 30 MHz was ready developed and handed over to the ITU-member countries in 2003 at the occasion of the WRC in Geneva/Switzerland. Since then it was successfully tested mainly in Europe and is ready for market entrance since 2005. Several receivers are available for different markets and new models are under development.

With the decision of the Indian Government in 2007 to modify all existing short- and medium-wave transmitters for DRM usage and a series of tests in 2007 the interest has increased not only in India. The presentation gives an overlook about the global situation as well as an outlook about the development of DRM+, an extension of the existing system for the FM frequency bands.

Digital Radio Mondiale - New Experience

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Digital Radio Mondiale - New Experience

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ABOUT THE SPEAKER

Since 1965 with Deutsche Welle, Germany and after 16 years abroad he was in charge of all terrestrial and satellite networks. In 1994 he became first chief engineer, than Director Distribution and since 2006 he is DW's Director DRM.

Peter was co-founder of the DRM consortium and is its chairman since 1998.

In September 2003 he has received the first life-time award of the European Broadcasting Union for his engagement for international broadcasting.

He is a member of the German National Platform for Space Communication and Navigation at the Deutsche Luft- und Raumfahrt.

Mr. David BirrerThomson Broadcast & Multimedia AG, France

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Abstract

In the past years Thomson Radio Broadcasting has focused its efforts on developing advanced solutions to meet the rapidly changing global frame conditions. The field of radio broadcasting is strongly affected by evolvements in the environment and technology, like global warming, soaring energy prices, scarcity of renewable energy sources, rapidly evolving digital media platforms, advances in compression technology and quickly changing life styles.

Meeting these challenges, Thomson offers more efficient transmitter solutions for digital and analog broadcasting and better protection devices against major natural phenomena like lightning.The purpose of this presentation is to give an overview of the status of DRM and new developments in the field of AM broadcasting.

Innovations in AM Broadcasting

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Field-proven high-power tube technology is 1. Introductionmaking way to solid-state solutions.

We are living in very challenging times with quick-Stationary, analog listening is making way to mobile paced environmental and technological changes.digital listening: the world is going digital and

Energy sources are getting scarce and costs are mobile!rising. In October 2003, a barrel of crude oil cost

In March 2008 DRM $30. On November 9, 2007, the price was ( D i g i t a l R a d i o $96.32/barrel. That’s more than 300% price M o n d i a l e ) increase in 4 years!organizat ion wi l l

You might ask yourself: what do environmental celebrate its 10th changes have to do with radio broadcast anniversary.technology?

After only ten years, The fact is that broadcast equipment suffers heavily the DRM consortium from natural phenomena like increasing lightning has developed a new effects in connection with global warming. digital system for all

broadcasting bands At the same time, broadcasters with high power from 150 kHz up to 108 MHz, enabling all radio broadcast equipment suffer under the strong stations around the globe to take part in the new increase of energy costs and need more energy-multimedia age.efficient solutions.

In October 2007, 40 broadcasters are using DRM Nature is avenging herself for the global warming: for regular transmissions with a total of about 800 reports about new floods, tsunamis, typhoons and hours daily. DRM has become an important other natural disasters appear practically weekly.member of the new digital media platform.

Today we can listen to a program in DRM coming from thousands of kilometers away in crystal clear FM quality! Ten years ago, who would have believed that this could ever be possible?

Thinking beyond the border is more important today than ever.

I would like to inform you about some of the latest innovations coming from the house of Thomson.

Thomson is committed to technological leadership since more than 70 years. Our goal is to develop cutting-edge technology and to put that technology at the disposal of our customers in the form of

In technology, the trend to digital and mobile is sturdy, reliable broadcast solutions.

accelerating in leaps and bounds. Media platforms are changing rapidly. 2. Increasing System Availability and

Protection against Enhanced Lightning Radio broadcast technology is forced to revise its classical technological approaches to meet the new Effectsdemands and to be prepared for the new challenges.

Statistics indicate that around 5’000 thunderstorms

Innovations in AM Broadcasting

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occur simultaneously worldwide with danger for A study showed that in the Darwin area, only 1°C persons, structures and material. Even in Europe, global warming results in 800% more lightning each year millions of Euros are spent for repairing strikes.damages from lightning. The density map below

Lightning protection is especially important for the gives a good picture of lightning activity worldwide.

new solid-state technology. The power vacuum The average intensity of a lightning flash is tubes of yesterday could withstand very adverse estimated to be 40’000 amps/µs. At the peak, even conditions like high transients coming from intensities of up to 200’000 amps have been lightning and the antenna field, and still keep on registered as well! working.

A lightning strike no thicker than a few inches can Today’s solid-state devices have a lot of advantages, illuminate one million 100- watt light bulbs! but they are very sensitive to such transients as

mentioned above. A few micro-seconds of over-The chart below depicts the increase in lightning

voltage or over-current can completely destroy occurrence versus the increase in average global

them.temperature in three different geographical zones.

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Broadcast antennas are the interfaces between nature and transmitter. Standing high and frequently at quite isolated places, broadcast antennas and especially connected equipment are highly vulnerable to lightning.

Especially medium wave radio broadcastings stations rely on high antennas (lambda/2 to lambda/4) in order to provide a greater signal coverage.

Thomson antenna specialists work hand in hand with our transmitter specialists to provide advanced protection for the overall systems.

Our special bandpass filter provides not only excellent lightning protection for solid-state

In digital mode (DRM), the savings potential is systems but is also a very useful device for quite amazing. A Thomson DRM transmitter compensation of nonlinear impedance and phase consumes only around a third of the power of an characteristics for DRM (Digital Radio Mondiale) analogue transmitter to cover the same area in even applications.better quality.

3. Overall System OptimizationThe vast field experience gained over 70 years of broadcast engineering has convinced us that A high overall efficiency of the complete building equipment based on tolerance design is transmission chain can save broadcasters literally always a wise decision.millions of dollars over the component life cycle of

20 or more years.Thanks to tolerance design, Thomson equipment withstands the wear and tear of day-to-day, around-A transmitter with a 5% lower purchase price today the-clock operation and pays off in terms of low, might end up costing you many times more over the longterm maintenance costs.years for energy and maintenance if the system

efficiency is not optimized.4. DRM Advances Worldwide

Looking at the efficiency of the overall system, we The media landscape is changing rapidly together see that it can range anywhere from 30% to 75%, with fast-paced developments in coding and depending on how much of the energy taken from compression technologies. the mains will finally be transmitted to the specified

target area. DRM is an important platform within the transition to digital media. A perfect complement to other Responding to the growing need of broadcasters to standards like DAB, DMB, HDRadio in FM, etc., reduce energy consumption and operating costs, DRM provides the possibility to transmit added-Thomson makes important advances in newest value services which can be used in parallel to the energy-savings technology. Our teams are pure audio and/or video programs.specialized in optimizing overall broadcast system

efficiency. DRM is the only economically applicable digital system to cover large areas over long distances. A Thomson transmitters can operate in various whole continent can be covered with only a few energy saving modes like DCC and AMC that transmitters and frequencies with near FM audio reduce the transmitter energy consumption up to and reception quality. 50% as compared with the classical DSB (Double

Side Band) mode. DRM can also be used like FM for local coverage

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with very low power shortwave transmission in the The interest in DRM is growing in leaps and 11 m-band (26 MHz). This found great interest bounds. The ABU (Asian Broadcasting Union) has worldwide as it can be used instead of FM when all been very active in conducting highly professional frequencies are already occupied. Using adequate tests and symposiums in various countries.antennas with reduced skywave propagation, local

A landmark event for digital radio took place in stations can operate with high quality audio and data

spring 2007 in India, where for the first time in the in this band.

world an 18 kHz DRM test was carried out in the Options like Multi-Frequency Network (MFN), medium wave band by Thomson.Single Frequency Network (SFN) and Single

The project was a huge success and listeners were Channel Simulcast (SCS) make very efficient use of

thrilled when they heard the crystal clear sound the existing spectrum.

emanating from their receiver sets.

Having seen the results of these tests, India is now fully committed to DRM and DW (Deutsche Welle) has recently taken up regular DRM shortwave broadcasts to that country.

DRM uses the same frequency, spectrum and channeling as analog AM and is the most cost-efficient, reliable and independent means to reach millions of listeners at home, on the road, at work or traveling or living in distant countries.

With the impact of globalization, one out of every New Zealand is using a Thomson DRM shortwave

35 persons on earth today is living abroad. for regular coverage of Pacific Islands, using the

International immigration is a fact and is growing. high-quality DRM signal for re-broadcast through local stations.China is one of the strongest and fast growing

economical powers in the world today. One out of Mexico and Brazil have participated in DRM tests

every six people in the world is from China and over with convincing results.

the last decade, millions of Chinese people are living abroad in various parts of the world. With The first Russian DRM symposium, cosponsored DRM, these groups can be serviced economically by Thomson, took place in October 2007. The and in high quality with programs coming from interest in DRM in that country is overwhelming. their home country. As a result of the symposium, a Russian car

manufacturer is going to place an order with a As the DRM system is developed for dayand night-

Russian receiver company for 100’000 DRM car time coverage (ground and sky-wave), it is proved to

receiver sets! In 2008, the Russian regulatory body work even under severe conditions like high man

will officially recommend the DRM standard.made noise in cities as well as difficult propagation conditions. For large African countries, DRM offers a unique

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possibility to participate in multimedia broadcasting of listeners around the globe with simultaneous for reasonable prices. access to data from one transmission site. There is

no other media with similar cost-effective Several African countries have committed

distribution possibilities. themselves to a DRM future with projects in implementation on 26 MHz for local coverage, on In comparison, simultaneous access of the Internet medium wave for local and national coverage and by only 10% of these listeners numbers would on short wave for national and international block lines and cause server break downs. DRM is coverage. reliable, secure, safe and independent, controlled

only by the broadcaster himself.The European continent is still a radiocontinent, which is also reflected by the high amount of DRM A highly fascinating option made possible by DRM transmissions originating in Europe or transmitted and DAB is called Journaline®, a new data towards Europe. application which provides the functionality of an

electronic newspaper.50 hours DRM transmissions are broadcast daily towards North, Central and South America, third As a kind of “teletext” application for digital radio, place after Europe and Australia/New Zealand. Journaline® carries both program related

information (general station presentation, listener contact information, background information on shows, etc.) as well as program unrelated information like news, sports, up-to-date financial/stocks information, weather forecasts categorized by region, etc.

The user can navigate through a menu structure and interactively find the required information on demand - right when he needs it.

The car manufacturers are offering data services in DRM/DAB based on News Journaline® for big events like for sports, etc. The basic idea of the proposed service is to transmit text-based information to vehicles and other mobile radio receivers.

The fascinating coverage possibilities of the AM 5. DRM Receivers: News from Chengdu

bands, united with the digital technology, high compression and increased bandwidth options, An overwhelming success of the DRM technology open the door for exciting new applications. Today’s depends on the widespread availability of DRM transmitters can broadcast music, speech, affordable, multi-functional receivers.data and pictures all at the same time on the same

The receiver set industry is moving quickly now and frequency. the official DRM website is updated regularly with

With 8 or 10 kHz bandwidth, a DRM transmitter the latest information. Basically there are 3 different can broadcast today a net bit rate of 20 kbps x 3600 types of DRM receivers: Software receivers, DSP seconds/hour x 24 hours/day x 7 days/week. This (Digital Signal Processing) receivers based on amounts to 1.5 giga bytes per week! Radioscape module RS500 or similar and chip-set

receivers. Depending on frequency, transmitter power, type of antenna, target area and time of day, DRM can Advantages of chip-set receivers include low price, provide on shortwave 5 to 6 hundreds of millions less power consumption, portable devices are

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6. Summary

Today, with the exciting new possibilities provided by DRM, there is no limit to what radio broadcasting can do.

After more than a hundred years, it is still the only media to reach out around the globe and inform and entertain people anywhere using a single, independent infrastructure from the own home territory.

possible and flexible combination with other digital The teams at Thomson Broadcast & Multimedia are systems in a single device. totally committed to the future of radio

broadcasting. We work hard to provide our Thomson is proud to have the opportunity to work customers with the best, most innovative and most together with a dynamic, young Chinese team at the cost-efficient equipment available anywhere today.Chengdu New Star Electronic Company, who has

designed a brand new, portable multifunction digital It is a pleasure and honor for us and our teams to radio set based on an Intel-chip-set. work together with the teams at AIR and other

broadcasters to bring a bright future to the The New Star WR608 is the first receiver with a high broadcast platforms in India.resolution color display, enabling new applications

like distance learning and picture radio. New Star has packed all the DRM functionalities that listeners are looking for into a neat, portable model and are bringing it to market at an unprecedented attractive price.

ABOUT THE SPEAKER

Mr. Birrer has been active in the broadcasting business since 1999. Beginning as a commissioning engineer of high power AM broadcast transmitters for Thomson Broadcast & Multimedia AG business unit in Switzerland. Birrer was responsible for commisssioning and handing over of various large broadcast transmitter projects worldwide. Since 2006, after serving as head of the project management group of the transmitter department, Birrer is Director of Marketing & Strategy of the Thomson Radio Transmission group.

2004–2005 Birrer has been appointed by the Managing Director of Thomson Broadcast & Multimedia AG in Switzerland to set up the wholly owned Service Center in Beijing, China.

Birrer has several diplomas, including diploma of electrical engineering (1998), postgraduate diploma in Business Administration (2003) and a Masters Degree of Business Administration (Executive MBA, 2005, at PHW Private Hochschule Wirtschaft, Zürich) and Cambridge International Management diploma in Marketing Strategy (University of Cambridge, London).

David Birrer was born 1975 near Lucerne in Switzerland. He is married and has one daugther.

Guy GampellAPT Broadcast

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Abstract

This paper seeks to examine the variety of trade-offs that must be considered when audio is compressed. It will provide an overview of both psycho-acoustic and ADPCM-based compression algorithm principles looking at the issues of latency, potential “loss” and concatenation associated with each approach.

Research findings will be presented incorporating theoretical and real-world latency figures, comparisons of sample material before and after compression and listening test comparisons after multiple encode / decode cycles.

New innovations in audio compression techniques such as AAC HE and apt-X Live will be explored and appraised. Lastly, with the advent of IP and the exponential increase in available bandwidth, this paper will consider if compression is still a requirement or if “Linear” is the answer.

Audio Compression – The Trade OffsBetween Quality, Data Reduction And Latency

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audio compression algorithm or codec for a 1. INTRODUCTIONbroadcast application lie in qualifying its latency,

Digital Audio Compression technologies are robustness and its audio transparency.utilized in a wide variety of audio distribution and

There are two fundamental audio compression storage applications. While these technologies bring processes currently employed:many benefits, compression also contributes

latency and can have a negative impact on the Perceptual: These are based on psychoacoustic perceived audio quality. models of hearing.

In its most directly encoded linear form, digital Predictive: These employ a system of predictive audio requires 1.411kbps - almost the entire coding and are known as ADPCM codecs.capacity of a 1.5Mb per sec T1 circuit to achieve CD resolution (16 bit stereo, 44.1Khz sample rate) Perceptual codecs – An Overviewaudio transmission. This carries significant The theory of perceptual coders is that of aural and penalties in terms of the operating cost of circuits temporal masking, taking advantage of two and distribution and is particularly inefficient when properties of the human auditory system: Spectral dealing with multiple channels. Therefore, for many masking (whereby frequencies of high amplitude applications, data compression is essential. “drown out” nearby higher or lower frequencies of

low amplitude) and temporal masking (whereby With a single encode-decode cycle of high quality loud aural events “drown out” quiet events audio compression, an average listener can rarely immediately before or afterwards). For the purpose detect coding. However, problems develop when of Spectral Masking, most psychoacoustic audio is passed through multiple encode-decode algorithms split an audio signal into a small number cycles - this effect is referred to as concatenation.of critical bands. Within each band the human ear

In research conducted by the EBU, it was identified has difficulty differentiating between cooccurring that typically, a broadcast chain consists of the sounds, so that sounds of higher volume or lower following elements: frequency will mask others within the same band.

Temporal masking is dealt with by dynamically Source

adjusting the input between long and short signal Contribution circuit

blocks to identify and mask any desirable effects of Broadcast studio installation sharp temporal sound.Secondary distribution

Development of perceptual codecs has been largely Emissiondriven by the desire to lower bit rates further and

Due to this growing number of ‘jumps’ and storage further, in part to cater for the consumer market points used in the broadcast chain, and the varied which has seen an explosion in the adoption of compression techniques employed, it is important portable devices (not just MP3 players and iPods to choose your audio compression technology but phones too) for audio storage.wisely.

Predictive codecs – An OverviewThis paper looks at the options for compression,

The theory of ADPCM or predictive coding their relative benefits and disadvantages and

operates in a fundamentally different way, not least suitable applications.

because it does not rely upon the removal of certain parts of the audio signal in order to reduce the bit 2. COMPRESSION TYPESrequirement for transport. Hence, predictive

The basic criteria for assessing the suitability of an coding is non-destructive.

Audio Compression – The Trade OffsBetween Quality, Data Reduction And Latency

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ADPCM coding takes advantage of the fact that it Where such delivery is distributed via terrestrial or takes less information to code the difference satellite using a psychoacoustic algorithm, special between two separate and successive audio samples care needs to be taken over contribution and compared to using their actual values. Since the distribution circuits so as to avoid concatenation early days of ADPCM algorithms such as G.722, (the detrimental effects of multiple encode/decode the technology has developed significantly and, in cycles).the form of Enhanced apt-X, it is now capable of

As shown earlier, the modern broadcast operating at multiple bit widths of 16, 20 or 24bits.

infrastructure has at least 5 “hops” or storage points Development of predictive codecs has been largely where several different audio codecs can be used. driven either by the desire to maintain low delay The EBU identified that for example, in the (latency) or the need to keep audio quality at its contribution element as many as 13 different codecs highest possible. were in use in a sample of broadcasters. Taking into

account all possible scenarios, one would arrive at a 3. APPLICATIONS total of over 50,000 possible codec combinations!

Clearly, when choosing a codec, the broadcaster Low delay being one of the key attributes of needs to think, not just about the stand-alone ADPCM coding makes it particularly suitable for performance but the entire broadcast chain.use on remote live links. A pronounced delay in this

application can cause confusion in the contributor This factor will be examined further in the paper.and affect the consistency of the live broadcast. The

4. THE EFFECTS OF AUDIO encode/decode cycle is not the only contributor of delay in broadcast applications: the additional COMPRESSIONinterfaces that need to be bridged in order to get the The purpose of this section of the paper is to signal onto an ISDN or leased line introduce their investigate different manifestations of audio own latency into the process - usually about 15ms. artifacts that occur as a result of compression based Given this fixed delay, it is important to minimize on the dynamic characteristics of audio content. I the additional variable delay from audio coding. will also examine how different types of program Predictive codecs will introduce far less latency into material can be affected by audio compression and the signal than a perceptual codec i.e. less than how these processes can affect the logistics of audio 1.98ms. transport and application demands.

Perceptual codecs take a significantly longer time to Content and Artifactscomplete the encode/decode cycle, for example, Loosely speaking, in audio compression, simpler is modules utilizing MPEG compression types will not easier. To encode and decode simple sounds typically create a latency of up to 120ms in each without detection is more difficult than to encode cycle and should be avoided in circumstances where and decode a complex audio signal such as an entire a low delay is crucial to the quality of the broadcast. orchestra or rock group. When testing audio

compression algorithms, the most unforgiving One of the most popular forms of compression source material to use and that used by many applied in such situations is the ADPCM codec researchers is that of isolated pitch pipes, Enhanced apt-X. Enhanced apt-X can transport 4 x glockenspiels and other sound sources of similar 20K stereo signals of 384kbps across a 1.536Mbps dynamic characteristics.T1 circuit and maintains 98% of the original signal.

Classical music is hard to compress due to the high Where latency isn’t an issue, and the pursuit of transience between the bass and treble, this could lowest possible data rate is paramount, perceptual also be said for an acapella female voice and a male coders are often chosen. An obvious example of voice with low tones. Even local language dialects this would be for final delivery to the consumer (e.g. and speech attributes can cause anomalies in audio DAB, IBOC, and streaming over the internet etc). compression.

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Musical instruments such as the tin whistle generate unavoidably induced into the audio signal during audio signals that are mostly tonal in appearance. the conversion to digital. As this noise determines Such signals contain a high level of redundant the maximum dynamic range achievable, the higher information in that most of the energy of the signal the quantization resolution the better the dynamic is concentrated in a small range of frequencies, range.principally at the fundamental note and higher

Figures are as follows:frequency harmonics. On the other hand, the signal from a cymbal is more like a noise signal in 16 bitappearance and contains very little redundancy in

Theoretical 96 dB, in practice usually around 85– that the energy of the signal is evenly distributed 90dB.across a wide range of frequencies.

24 bitIt is important to note that the waveform of an analog audio signal is time and amplitude Theoretical 144 db, in practice usually around 110-continuous whereas a digital signal is time and 120 dBamplitude discrete according to the sample rate and

Data compression can be seen as another stage of quantization resolution (number of bits).quantization added to an already quantized signal

Before proceeding, some notes of explanation are and, depending on the accuracy of the quantizer, required: will simply induce more quantization noise. This is

an accumulative process and it is easy to see that, if Sample rate is a measure of how often in a given the process is continually repeated, then there will period (1 second), a quantization measurement come a time when the quantization noise is audible.takes place. A minimum of two samples is required

to encode a given pure frequency waveform When encoding a PCM signal, a perceptual coder therefore an audio bandwidth “f ” requires a sample allocates the reduced bit rate in a way that attempts rate “2xf ” to encode it. In practice it is common to to maintain a separation band or threshold between use higher sample rates, since the process of the wanted audio signal and the quantization noise - sampling also creates noise (called aliasing) which is a masking effect.an image frequency of actual sample rate +/- f. A

However, repeated passes of perceptual encoding filter is required to remove this out of band noise may very quickly erode this threshold and soon, the and, if too aggressive, such filters can affect the quantization noise breaks through this threshold performance “in band”. A higher sample rate and is audible. In predictive encoders the requires a less aggressive anti-aliasing filter for the quantization noise is restricted within each of a same audio bandwidth or can be used to provide a number of subbands. The subband quantizers, wider audio bandwidthprocessing only very small differential signals, are

Quantization is the process of encoding the effectively insulated from each other and the amplitude of an analogue audio signal: the higher quantization noise induced in one subband does the number of possible quantization values offered, not influence any of the other subbands. The the more accurate the systems encoding is. A 16-bit overall effect is that an audio signal can withstand system such as CD offers 2 16 possible discrete any more passes of predictive encoding than an quantization values. i.e. 65,536 possible values equivalent perceptual encoder. Awareness of these whereas a 24 bit system offers 16,772,216 possible effects is of ever-increasing importance as more values. Of course the actual signal level will usually instances of digital compression are added to the fall somewhere between two possible quantization broadcast delivery chain.levels. The difference between the two levels (actual

Perceptual encoders operate in the frequency and quantized) in itself is an error which is a form domain using the theory that loud sounds will mask of distortion known as quantization noise and in out the quieter sounds. The analyzed sounds are

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subjected to a masking process that removes all those irrelevant parts of the audio that would never be heard. It will depend on the nature of the audio signal as to how much irrelevancy is removed but it could be as much as 80% of the original signal. If the audio signal is subjected to other passes of compression that involve other types of perceptual encoding then there can be a conflict between the competing masking models. When different types and levels of perceptual encoding and decoding are applied over a number of ‘jumps’ in the broadcast chain, the problem of concatenation may occur and

[B] Next is a comparison between the original PCM very quickly degrade the audio signal.

of above, and a single Encode/Decode cycle using Predictive encoding operates solely in the time MPEG.domain. Filtered subbands of the PCM signal are analyzed to identify those parts of the signal that are repetitive, a common feature of all PCM signals. Once identified, the sample levels are measurable and readily predictable and this prediction can then be compared with the actual sample. The resulting low-level differential signal is now all that is required to be requantized to a lower bit resolution. This is then multiplexed with the reduced data from the other subbands to represent the original linear PCM audio signal. Such an approach is known as redundancy removal and this theory is extended to the decoder which uses the same prediction process

High the level of harmonic distortion between to re-introduce a similar amount of data to the

20Hz and 2Khz apparent by the wide variation in decoded differential signal, thus reconstructing the

frequency content shown above between the original linear PCM signal. In an end-to-end

original and the MPEG encoded signal.process, the accuracy of both prediction processes delivers around 98% of the original signal. The A very large amount of spectral content has been minimum signal loss at each pass of predictive completely removed between 6Khz and 9Khz, with compression means that many more passes can be almost total content loss between 7Khz and 8Khz. tolerated without audible degradation. This is repeated with a very large amount of spectral

content removed between 12Khz and 15Khz and Illustration and Demonstration almost total content loss between 13Khz and

14Khz. There is a high level of harmonic distortion By way of illustration lets look at a recording of the between 14Khz and 15.5Khz, a steep roll-off above singer Suzanne Vega singing a well know song of 15Khz and no content over 16Khz.hers, solo, unaccompanied.

Listen to MPEG 1 time encoded/decoded.[A] This is the original after PCM encoding (linear uncompressed audio at CD resolution) Why does it work? Well it works for the reasons

explained above, in that content removed has been Note the surprising complexity of harmonic done so according to wel l researched content from a single source (solo singer), the psychoacoustic prediction that this is the content complex harmonic structure continues to 20Khz that will not be audible. However this does not bode with a gentle roll off from 20Khz to 21Khz.

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Listen to Enhanced apt-X after 5 times encode/decode.

5. CONCLUSION AND SUGGESTIONS

Broadcasters seeking the best performance from their infrastructure investment will inevitably have to seek the best possible trade-off between the quality, data reduction and latency offered by their audio delivery compression.

Digital Transmission systems such as DAB (Eureka 147) or HD Radio (formerly IBOC) specify the use

well for a second, third or fourth encode/decode of perceptual codecs, such as MPEG or AAC cycle. Since it is accepted that a typical broadcast respectively, for final transmission. They also chain involves up to 5 hops or storage points, this is specify the desired compression ratio, which in the critical. case of HD Radio is 12:1. Given these constraints,

care needs to be taken with the choice of Let us have a listen to what happens.compression used in any prior stage of the program

Listen to MPEG, 5 times encoded/decoded. chain. Any loss incurred earlier in the chain cannot be recovered and incremental losses can be [C] Finally, a comparison between the initial PCM disastrous.encoding and a popular ADPCM type of algorithm

(Enhanced apt-X). The use of perceptual algorithms elsewhere in the production chain (location “Flash Memory” The preceding is an FFT plot of the same audio recorders, storage and play out systems, presenter’s after one encode and decode cycle of Enhanced personal MP3 players, Mini Disc etc) also adds to apt-X data compression running at 16bit, 44.1Khz, the requirement for an ADPCM algorithm to be data rate of 384Kbps.used for distribution.

Note that Spectral content is preserved very Therefore, the safest choice is to use the highest bit accurately including complex harmonic structure rate possible or, put another way, the lowest and high frequency content.compression ratio. In parallel with this, the

Listen to apt-X 1 time encode/decode processing delay should also be kept at a minimum for broadcasting consistency.

ABOUT THE SPEAKER

Mr Gampell has approximately 25 years experience in the recording, post-production and broadcast industries. Gampell has been a key player in the introduction and adoption of many new digital technologies in that time, and now works as the Asian Sales Manager for APT. Gampell has overseen tremendous growth of business for APT in Asia, especially India, where in the last 12 months APT has shipped in excess of 450 codecs to customers in India. Today's talk will reveal what the key issues are that broadcasters need to be considering when choosing the right technology for the application of audio distribution and contribution.