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March 1993: Volume 1, Number 3

The Acoustics of Musical Instruments for Audio Engineers

John M. Eargle, JME Consulting


Pre-meeting "Dutch Treat" dinner, 6:00 pm at "On the Rocks" Restaurant, 169 Front Street East (near S.W. corner of Sherbourne & Front)

AES What's Inside

AES This Month's Meeting Preview

What Every Engineer Should Know about Sound

This month's meeting will feature a guest speaker known to many of us as colleague, author and audio recording guru.

John Eargle holds degrees in engineering and music from the Eastman School of Music (B.M.), University of Michigan (M.M), University of Texas (B.S.E.E), and Cooper Union (M.E.), was with the quality control department of RCA Records, and served as Chief Engineer for Mercury Records. During the seventies he worked for the Altec Corporation and formed the firm JME Consulting Corporation.

Since 1976, he has been associated with JBL Incorporated, Northridge, California, in the areas of product development and application. He is a Fellow and honourary member of the Audio Engineering Society, and is a past President of the AES. He is a reviewer for the AES Journal, is a member of the Acoustical Society of America, the SMPTE, the National Academy of Recording Arts and Sciences, and a senior member of IEEE. He has published extensively in technical and popular magazines, as well as penning standard reference books on audio, including Sound Recording, Handbook of Recording Engineering, The Microphone Handbook, and Handbook of Sound System Design. He is active as a recording engineer, having now engineered and/or produced over 60 Compact Discs, and much of his work can be heard on the Delos label.

Mr Eargle will give a presentation which will cover aspects of musical instruments that are useful for audio engineers in recording, broadcasting, and sound reinforcement.

The presentation will start with a discussion of the basics of sound generation, including: oscillating systems, their power relationships, the bandpass nature of instruments and preferred frequencies and formants; the control of pitch by valves, crooks and keys, by strings, tension and mass per-unit length, and the resulting harmonics and non-harmonic overtones.

A discussion of the acoustical radiation characterisitcs of acoustic instruments will focus on the spectral characteristics with regards to the frequency ranges of instruments and relationship to size, the change of spectral characteristics with playing level, the powers radiated by acoustic instruments, and the relationship between instantaneous, peak, long term average and short term average powers from instruments.

The radiation patterns from various instruments will be examined. This will include estimating the types of radiation patterns for the instruments-- omni-directional, bipolar, and directional; the instrument size, frequency range, and patterns, and the effects of nearby boundaries.

The presentation will conclude with Mr Eargle's thoughts on some of the practical engineering considerations he is able to give from his many years of experience as a well-respected recording engineer.

Thanks to Neil Muncy for additional bio information.

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AES Last Month's Meeting Review

Despite a minor snow squall, dumping amounts of precipitation not uncommon to the Great White North, Dr K Raj managed to safely arrive here inToronto, where about thirty committed loudspeaker enthusiasts attended a very informative presentation on the state of the art in ferrofluids.

The opportunities for the use of ferrofluids have increased in loudspeaker design in recent years, mainly due to improvements in ferrofluidic technology for which Dr Raj's company Ferrofluidics Corporation is largely responsible.

Many of Toronto's leading loudspeaker designers and installers were on hand to question Dr Raj and to learn about the kind of suppport Ferrofluidic Corporation can offer loudspeaker designers who wish to use ferrofluids in their products.

We also picked up a few hints on how to handle ferrofluids, one specifically on how to go about removing the material from a voice coil... a messy task indeed!

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AES Announcements

How to Pay your Membership Fee

As we reported in last month's newsletter, there has been a change of policy regarding payment of new and renewing AES memberships.

AES Toronto has learned that a recent increase in bank charges (to as much as $50.00) has made cashing cheques drawn on Canadian accounts obviously impossible for AES International. Previously, the $10.00 charge for such cheques was absorbed by the AES.

Until a solution can be found, if you are unable to pay your dues with a major credit card or a cheque drawn on a major US bank with offices in New York City, please forward your payments to AES Toronto, Box 292, 131 Bloor St W, Suite 200, Toronto, Ontario, M5S 1R8.

AES Birth Announcement

This month, in an effort to attract new members to the AES, two executive members, all in the line of duty, have made proud achievements.

The Executive Committee of the Toronto Section would like to extend their congratulations to: Earl and Karrie McCluskie on the arrival of their son, John Alexander, and Martin and Wendy Fraser on the arrival of their son, Devon James.

A wish of health and happiness to both families!

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AES Feature

Desktop Radio at the CBC: The Beginning of A New Era

CBC Radio News, with the move into the new Canadian Broadcasting Centre in Toronto, is nearing the end of the analogue tape/razor blade era for the recording and presentation of news reports.

The basic process still in use has not changed in decades. Incoming news items must be recorded, properly labelled and logged, double-recorded or dubbed before editing if needed by more than one program with different edits, edited by the time-honoured splice method (hopefully without useful material being cut out and discarded), transcribed to hard copy, placed in a stack for airing in the proper sequence, played to air, and saved or even re-edited for further use. While the tapes are being handled by a sequence of highly skilled specialists, they must also survive mechanical handling on reel-to-reel machines that are literally in use around the clock.

Replacing all this will be a recording/editing system called Desktop Radio that is computer controlled, based on digital audio and, of course, tapeless.

The name Desktop Radio does not refer to a small receiving device that lives upon one's work surface, but rather to a system that allows preparation of recorded audio for radio broadcasts analogous to the way that Desktop Publishing is used with text and graphics.

A really exciting aspect of CBC's Desktop Radio system is that it will be put into operation in the CBC Englsih Network Radio News operation this year.

One of the main factors motivating the timing of this major shift in technology is the move, just now beginning, of CBC's Toronto-based operations into the new Canadian Broadcasting Centre. With all studio facilities finding a new home, the opportunity existed to replace aging analogue reel-to-reel machines with something quite different.

A great deal of pioneering work in the new digital audio technologies had been done in a CBC pilot project called the AAPF (Advanced Audio Production Facility), built in Studio H of the old Toronto Radio Building in 1989. This studio utilized digital recorders and random-access editors, interconnected not via the usual analogue audio ports, but fully digitally, as well as mixing in the digital domain. Many important lessons were learned from both the operational and the system engineering viewpoints, and while the teething stage was difficult, the facility has become one of the most popular in Toronto Radio.

Armed with this experience, as well as an extensive survey of present and desired operational techniques in Radio News, the design team came up with the final system, which I shall now describe.

While the various specialists who make up the Radio News production process will still be in place, their tools will look quite different. The various banks of reel-to-reel machines for recording, editing and playback found in each workroom will be replaced by networked computer workstations, including specialized "machine transport" control surfaces for each job function. News items arriving from a variety of telecommunications sources will be recorded onto hard disk, edited non-destructively and by many different editors simultaneously if required, and played to air in a preset or manual sequence from the disk. The transcription of the items, as well as the writing of announcer scripts, will be keyboarded in multi-tasking mode on the same machine used for handling the audio. A probable future development, for which today's technology is not yet quite ready, will use speech-to-text translation to create the transcriptions, with interactive text and audio editing.

While there are presently a number of very good microcomputer-based hard disk recording/editing systems, for the most part these are one-user stand-alone products. The need in Desktop Radio for instant transfer between stations, simultaneous multiple access to items, managed archiving/retrieval, and various database and housekeeping functions for a massive amount of storage all make necessary a system with networking at its heart. CBC found a system which, with extensive customization, could meet the Desktop Radio specification. This system, known as D-Cart, had in fact been created by the Australian Broadcasting Corporation expressly for the radio broadcast environment, and early versions had already been acquired by several radio networks around the world.

Radio News is to be the first CBC recipient of Desktop Radio technology, and it will surely not be the last. The AAPF project has already created an appetite for digital audio/computer production techniques in many other program areas. While the initial system connects many users in one department, in the years to come there will be connection of many departments in a building, and many cities on a network, in much the same way.

In Toronto, Tom Shevlin, (P. Eng.)

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Logo Copyright 1993, Audio Engineering Society Toronto Section Bulletin

Articles may be used with the Author's Permission. Contact the Bulletin Editor: earlm@hookup.net

Editor: Earl McCluskie Assistant Editor: Anne Reynolds Layout Editor: Lee White

The Bulletin is prepared in print by Lee White, and on Horizons and the Internet by Earl McCluskie.