[Toronto AES Logo]

June 1 1993: Volume 1, Number 6


DSP Analysis and Correction of Room Acoustics


Special Event End of Year Social Following Meeting

AES What's Inside

AES This Month's Meeting Preview

Adjusting The Relationship between the Loudspeaker and Monitoring Environment

Loudspeaker designers have long recognized the influence of the acoustic environment on the perceived quality of an audio system. The availability of powerful digital signal processor integrated circuits has created interest in the application of adaptive digital filtering techniques to the equalization of loudspeakers in rooms.

This month's meeting will present a discussion of the issues which must be considered in order to address the problem successfully, and this will be followed by examples using a commercial implementation of these solutions in several different environments.

The presentation will be given by Ronald P. Genereux, Vice President, Cambridge Signal Technologies. Mr Genereux received his B.S. in Electrical Engineering from the University of Rhode Island in 1978, and then his M.S. in Electrical Engineering from the same institute in 1983. He is a co- inventor of US Patent #4,458,362 on Digital Correction of Room Acoustics and the author of three Audio Engineering Society papers on Analysis and Correction of Room Acoustics. He has been the Chief Development Engineer at Acoustic Research of ADSP technology (room acoustic correction) during the 1980s. This technology was acquired by SigTech (Cambridge Signal Technologies) in 1990, and developed into the AEC 1000. Mr Genereux is a member of the AES and the IEEE.

Cambridge Signal Technologies Inc of Cambridge, Mass. has recently introduced the production version of the AEC 1000. This is a DSP-based system that analyzes the acoustics of a room, and then goes on to create digital filters to correct problems at given seats. It operates in both the time and frequency domains, to correct not only conventional equalization problems, but also deleterious effects of early reflections.

The operator can intervene in the filter creation process via the PC interface, or modify the filter action to produce a target equalization curve, or provide a "compromise" correction that is valid for a number of simultaneous listeners. Several presets are available on a remote to provide a choice of system- generated and modified curves for various seats.

It has been well-received in both the professional studio environment (particularly by CD mastering facilities), and high-end home audiophile applications; this is the rare sort of product that gets positive reviews not only from Studio Sound magazine, but also Stereophile and Absolute Sound.

"The AEC 1000 system is intended to correct for certain deficiencies in the acoustics of the monitoring environment which are known to be key factors influencing perceived sound quality. When tested in an average control room with average monitors, it appeared to make significant improvements in the quality of the perceived sound. Whether it would do so equally well in other studios is something which must be assessed on an individual basis, but these initial tests bode well for at least some improvement in many rooms where the conditions are less than perfect." (Francis Rumsey, Studio Sound).

Up button What's Inside

AES Last Month's Meeting Summary

Flat-Response Attenuation, or "Plugs for Players"

On Tuesday, May 18th, approximately 50 members and guests were present to hear an important discussion on "Hearing and the Musician" by audiologist, Dr Marshall Chasin. Dr Chasin, who is also the Director of Research at the Centre for Human Performance and Health Promotion in Hamilton, was joined by Ian McIntosh of EDI Canada (distributor of ER products in Canada) to give an overview of earplug theory and design and to dispell some of the myths associated with hearing protection and ear safety. For example "you should never put anything larger than an elbow in your ear canal..." (ie. Q-Tips are great for cleaning tape heads but keep them out of your ears!)

Chasin began his presentation with a list of factors for musicians to determine how dangerous you are to your hearing and the hearing of those around you:

1. Your playing style or technique. Principal players and soloists tend to play louder than session and second line players.

2. The frequency range of your instrument and its related harmonic component. It is this high frequency energy that does the most damage.

3. The general size and shape of your instrument. Belled instruments such as the trumpet are very directional, especially in the high frequency range, and can be especially dangerous for the players in front of them.

4. Your proximity to the source of the problem. Obviously, the closer you are to the offending instrument, the more damage that will result. Also taken into account is the proximity of one ear to the source versus the other. Flute players, for example, play their instrument off to one side, which means that one ear is subjected to more of the harmful high end energy, and as a result may suffer more damage than the other. This can also inhibit the brain's natural ability to mask extraneous noise occurring in both ears at the same time.

All of this is taken into account when a musician arrives at the Centre to be tested. Specialized SP meters and probe microphones are inserted into the ear to measure exactly what the musician is hearing.

In their research, the Centre discovered that most of the hearing loss occurs between 3K and 6K Hz, regardless of the frequency content of the source. They also found that some of the hearing lost between 8K and 10K Hz has been known to return.

Chasin also warned us that the wrong ear protection can be just as dangerous as wearing no protection at all. He gave us the example of a drummer who went to his doctor complaining of a sore wrist. It was discovered that the drummer had been using industrial foam earplugs for the preceding six months. These earplugs provided over 30 dB of attenuation in the low end and a severe roll-off above 2K which resulted in the drummer over-playing to compensate, causing him to strain his wrist.

Chasin went on to describe two problems with conventional earplugs which preclude their use in most music related applications:

1. Whereas the low frequencies are attenuated only a small amount with conventional earplugs, the high frequencies are attenuated an additional 10 to 20 dB because of their smaller wavelengths. This poses obvious problems for the audio engineer and performer alike.

2. Conventional earplugs have a large occlusion effect. This results in the user hearing their own voice with a very boomy quality, which is just down-right annoying.

Therefore, to maintain the fidelity of the orginal sound and to provide equal attenuation at all frequencies, ER (Etymotic Research) came up with a series of "Flat-Response Attenuators."

The four basic designs:

1. ER-15 Musician's Earplug: a custom fitted deep seal plug offering attenuation, with a built-in resonator that puts back a controlled amount of the high frequency signal that is naturally attenuated by the physical presence of the plug in the ear. The net effect is a flat response of minus 15 dB.

2. ER-20 Hifi Earplug: a generic (non-custom) eartip. The response curve isn't as flat as the ER-15, but the price is more affordable.

3. ER-25 Musician's Earplug: a custom fitted deep seal plug offering 25 dB of attentuation with a built-in resonator as in the ER-15.

4. Vented/Tuned Ear Plug: a modified swimmer's ear plug with a 3 mm SAV (Select-A-Vent) drilled through the centre. Excellent in situations where the high frequency harmonic content of a musician's own instrument is not excessive, but he still needs protection from other players around him.

Other environmental solutions offered by Dr Chasin:

1. Putting directional instruments (eg. trumpets) on risers. That way they are "blasting" over the heads of the other players.

2. Increase the distance between the offending instruments and other players, also making use of baffles.

3. Rehearse in a large space.

4. Tilt or raise speakers off the ground so that they are not aimed directly at the performers' ears.

5. Believe it or not... long hair can give you up to 5 dB of attenuation.

In Toronto, Anne Reynolds

Want more information? Contact: EDI Canada (800)265-8250

Up button What's Inside



There was a healthy slate of candidates, a stimulating exchange of ideas was enjoyed during our nationally televised debates, none of the candidates has ever inhaled, the enemies of Canada still abound, Friday Night with Ralph Benmergui was fascinated, Joe Clark is disappointed but now safely ensconsed at the United Nations, and we have a nice tract of land in northwest Quebec we think you might be interested in.

The AES Toronto Section proudly announces the new 1993-1994 Executive!

By acclamation, the following candidates are ready to begin the new season:

Tom Shevlin,Chairman

Dan Mombourquette, Past Chairman

Denis Tremblay, Vice Chairman

Earl McCluskie, Secretary

Glenn Specht, Treasurer

Peter Cook, Membership Secretary

Janine Walton, Public Relations

Committee Members: Anne Reynolds, Martin Fraser, Devy Breda, Leo Lobos, Jim Cox, Colin Bernard, Paul Reibling

For more information about the Executive, check the April and May issues of the Bulletin.

Look forward to another exciting, event-filled year!

Who's Who: Floyde Toole, 1992-93 AES President

The 1992-1993 season introduced a new President to the Audio Engineering Society. Dr Floyd Toole studied electrical engineering at the University of New Brunswick and then received a Ph.D. from the Imperial College of Science and Technology, University of London. For many years he was a senior research officer in the Acoustics and Signal Processing Group at the National Research Council Canada. In November 1991, he became Vice-President, Acoustic Research, at Harman International, in California.

Dr Toole is known as an expert on loudspeakers and for his research into noise control, room acoustics and sound reproduction. He has authored several papers in the journals of the AES and ASA, contributed to two recent audio engineering handbooks and numerous articles in consumer audio publications, and is a familiar guest speaker at AES section meetings. Dr Toole has served as Vice- President/Eastern Region of the AES, and is chairman of the AES Standards Committee Working Group on Listening Tests.

When asked at the San Francisco convention in 1992 about his plans and expectations for the AES during his tenure, Dr Toole said his priority is to keep the society on track during a time of considerable change and growth. During his presidency, Dr Tooles hopes to attract new people to the AES, not just engineers, but people with an interest and passion for audio, people who work in the field and people who want to work in the field. In particular he wants to encourage young people to get involved. Recognizing the new European scene brings with it language barriers and people not familiar with the organization but who really need it, Dr Toole is nevertheless looking forward to the mass exchange of experiences and knowledge that is sure to follow.

If you had the opportunity to read the President's message in the November issue of the Journal, Dr Toole expressed his vision for the society and encouraged everyone to get involved. "If you have a point of view, if you are interested in something particular, if you want to do something for or with your audio colleagues, join in. You won't regret it."

In Toronto, Janine Walton


As many members of the Toronto Section certainly recall, the CBC Broadcasting Centre hosted us in a "hard hat" tour several years ago. The focus was on the sound isolation elements plainly visible in the bare concrete construction at that time. The attendance for the tour was over 200, spread over 2 Saturdays. Not surprisingly, there appears to be at least as much interest in seeing the working facility. Since most Toronto CBC Radio broadcasting, as well as Friday Night with Ralph Benmergui on TV, has been originating from the Centre for some months, many members have been curious as to why there has not yet been a return tour.

Your present Vice-Chairman has been a contract engineer designing radio studio systems in the Centre for the past 6 years, and here offers an update on the situation.

While the stereo broadcasting and production studios for most radio program areas are now functional and on the air, a great deal of work remains to be done in the multitrack recording studios. This includes the Glenn Gould Studio (a 350-seat recital hall with attached control room) which has been in use for broadcasts and recordings since Sept. '92, but with only a temporary stereo console and recorders. This facility, along with the replacement for music studio 4S and a mixdown room, will be fitted out this summer with Sony 48-track digital recorders as well as digital Neve Capricorn consoles. The section Committee felt that most members would wish to see the finished versions of these facilities on the tour; thus a target date of November '93 is presently being contemplated, to allow for substantial completion.

Another likely highlight of the tour will be the Radio Drama and Sound Effects areas. These are at present the last departments still operating out of the old Radio Building on Jarvis St, while an intense effort goes on to design their new studio systems. The one thing for sure at this time is that the primary multitrack recording systems will be tapeless. This will allow for comprehensive time manipulation of material, which is as important in Radio Drama as it is in TV post audio.

The much-discussed Desktop Radio system, a digital storage, editing and networking system for Radio News, is presently being brought up to speed alongside of the old analogue tape-based system. This system, possibly along with several offshoots in other areas, will probably be in full operation by tour time.

Television facilities will be under construction for many months yet. Possibly at least one of the multitrack rooms, which in TV feature the analogue Neve VR consoles, will be available for view in the '93 tour. The large sound reinforcement system purchased last year for the Benmergui show is completely portable, and its whereabouts at the time of our tour cannot be predicted at this time.

So, there should be a wide variety of both conventional analog and exciting digital audio facilities available for the '93 tour. Due to the nature of production schedules, it is likely that the tour will be held on a Saturday rather than our usual Tuesday night. Watch this space (after our Summer break) for further information.

In Toronto, Tom Shevlin

Thanks to two past Chairmen

The Executive Committee of the Toronto Section of the AES would like to extend their thanks to two past Presidents, Mr Ron Lynch and Mr Neil Muncy, for all of their hard work and many contributions to the Toronto Section over the years.

Unfortunately, due to increasing demands on their time, both gentlemen have decided to retire from the Committee.

Although they may be leaving the Executive, we hope to be seeing Ron and Neil at our monthly Section meetings for many years to come.

In Toronto, Anne Reynolds

Up button What's Inside

AES Previous and Next Issues

Back Back to May 1993

Forward Forward to September 1993

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.