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What's Inside
This Month's Meeting PreviewPeavey MediaMatrix and sound amplification systems
MediaMatrix is a combination of software and hardware used in the implementation of small, medium and large-scale sound systems. The number of inputs and outputs can range form 8 in/8 out to 320 in/320 out, and 10 levels of signal processing capacity are available. It has a graphical user interface that runs under the familiar Windows operating system and is very straightforward and intuitive to use. The designer simply selects the devices that will be included in the system, such as equalizers, mixers and limiters, places them on the screen, connects them together with graphical wires and issues the compile command. MediaMatrix then automatically creates the system that has just been designed. In a matter of moments an operator can audition the results and adjust the parameters.
Custom control panels can be easily made which include controls and meters from any device in the system, and five levels of password access insure that each staff member has access only to the controls for which they are authorized. An on-line help system is included which provides access to information on MediaMatrix. Presets for different configurations can be created. Each preset includes the setting of every knob, switch and fader in the entire sound system.
If a facility has a basketball game in the morning, a concert in the evening, and a convention the next day, each different mode of operation can be selected by pushing a button. If a delay is required on a balcony system, but was not included in the original design, it can easily be added. The system is easily expanded, modified, and updated to accommodate future requirements.
From the Head Office in Meridian, Mississippi, George Douglas, National Sales Manager and head of the Architectural Acoustics Division, and Ken Valentine, Eastern Sales Manager will give a presentation of the software.
Phil Giddings and Dave Clark of Engineering Harmonics will discuss specific design projects where they have used the MediaMatrix product.
To Boldly Go
Editor's Log: Star Date 01.01.1996
I'm a Star Trek fan. I like the characters, the story plots, the concept of intergalactic space travel and the notion that someday mankind might evolve into a truly caring civilization. But most of all, I like what computers can do for the crew of the Enterprise.
Commander Data exploring what happens when you throw Mozart, Bach, Ives and etcetera together all at once, Captain Picard ordering up some accompaniment to his flute playing, or simply announcing, "Computer, Earl Grey tea, hot".
Or Chief Engineer Jordi designing some new fantastic modification to the warp drive, simply by commanding the computer to move graphical elements around and connect them together. The lesson to be learned here is simple: technology can only continue to evolve if the human interface also evolves along with it.
The folks at Peavey, I'm willing to bet, watch a lot of Star Trek. Their MediaMatrix brings the design and operation of a sound system one large step closer for mankind to the Star Trek fantasy. It's only a matter of time before such systems respond to voice commands like "Computer, 10 dB up, FOH subs" or "Massage my pelvis, man".
The final frontier awaits.
Peter Moore was seen on @discovery.ca answering a question sent in by a viewer asking why it is our voices sound unexpectedly different to us when we hear them recorded, but other people's voices sound similar to what we expect. (Sound transmits through our skull to our ears when we speak, and we of course don't hear that sound when we listen to our recorded voice).
Live Wire has, not surprisingly, been busy as elves over the last month, recording for broadcast such acts as Meat Loaf, Def Leppard, Clint Black, Garth Brooks, the Dofasco Choir and Hamilton Philharmonic Youth Orchestra, Salome Bey, Molly Johnson, Maureen Forestor, Billy Newton-Davis, The Philosopher Kings, and the list goes on. Doug McClement received a quintuple platinum album from Warner Music for his live recording of Hootie and the Blowfish in Banff, Alberta in March for Much Music's Snow Job '95.
If you or an AES member you know would like to let us know what you're up to, just drop us a note.
Our year-end meeting and social was held at the Vibron plant in Mississauga, where Tom Paige gave us a lecture and demonstration of ionized-gas loudspeakers. He has pursued this technology for 25+ years, starting with his M.Sc. thesis. We were given copies of his and Prof. Hamid's August 1972 IEEE paper "Horn-Type Electrothermal Loudspeakers", describing the setup and results of a similar device.
The earliest type of ionized-gas speaker used RF excitation, heating air to a plasma; audio modulation of the RF power caused variable plasma heating, resulting in acoustic output. This type of speaker is still used for acoustic studies requiring kHz to MHz excitation, but is very inefficient.
Tom's demo setup starts with an acetylene or propane flame as the ionized-gas source, in the throat of a conventional (but flame-proof) horn. To obtain better electrical coupling into the flame (lower resistance), it is seeded with a dilute spray of dissolved potassium nitrate. A tungsten cathode in the flame tip carries a 700-800 V, 30 mA DC bias w.r.t. the burner (anode), to establish a linear-ionization class-A operating point, around which the audio modulation will vary.
An automotive ignition coil serves well as the audio stepup transformer, for driving the cathode. Careful setting of the bias gives decent linearity and stability, but the flame turbulence self-noise and uneven distribution of the seeding droplets beget only a 15 to 40 dB S/N ratio at various points on the 300-9000 Hz response curve. The demo confirmed this to us.
Most of Tom's recent work dealt with the mechanics of the flame seeding. The maximum acoustic output and efficiency depend heavily on the electrodes' gas-contact resistance. Tom demonstrated that the efficiency of simple resistive heating by audio power in air is much less than in the above demo, by feeding stepped-up audio voltage to a sparkplug mounted at the end of a horn. Crossover and clipping distortion were atrocious, of course, working in this non-linear region of operation, but we could hear the difference between sine-wave and square-wave tones. This illustrated that the flame-speaker is an active speaker, with some gain. Possible applications are in combustion processes (to improve efficiency by better mixing), or noise-reducing active transduction in a combustion-exhaust stream.
After the show we enjoyed our year-end social, strolling through the Vibron factory, identifying Helmholz resonators and other acoustic principles in the work-in-progress. An interesting time was had by all.
by John Fourdraine, Toronto
Ray Callahan, from Sony Cinema Products Corp., Culver City, California, gave his first-hand account of the history and technology of SDDS, Sony Dynamic Digital Sound, to about 60 of us.
SDDS is the outcome of Sony Cinema Products technicians and engineers getting tired of adjusting conventional (analog optical) movie-sound playback equipment, and thinking of a better way. A proposal was made, Sony management approved 18 months for development, using US and Japanese teams (the "synergy" program), and the rest is history. The SDDS was designed expressly for 35 mm film and optimizes every aspect of the available resources, such as the use of the outer film edges (370% more area than in between the sprocket holes), a separate playback "box" (for adaptability to any projector), and an all-digital approach, to gain reliability and independence of existing mechanical (noise) and audio limitations.
Research indicated that the marketplace did not want separate media, even though slaving a CD-based audio system to the film works well, and is much cheaper. Therefore the usual optical problems, such as variable focus, edge-distortion, edge-fogging (from poor production Q.C.), or scratches and oil on the film, were dealt with by 200 grams of film-clamping force onto the stabilizer drum, and encoding 12 digital tracks, (6 on each edge). Those 12 tracks contain the 8 discrete audio channels (4 on each edge), and 2 on each edge with backup redundancy information for the other edge. Each track also has its own separate redundancy. The ATRAC 5:1 data compression, level 2, is used for the audio channels.
Uncorrectable errors in any or all channels cause a 35 msec cross-fade to a backup. The left and right groups of 4 channels each are offset by 17 frames, so a splice or other multi-frame error is recoverable. The ultimate backups are the standard analog optical stereo tracks.
Red 12-LED arrays with multi-angle focus cause ordinary scratches to be "invisible" to the read heads. A 1200-pass film life is reported. The system bypasses an existing cinema audio chain, except the power amplifiers and loudspeakers. Options include PC-based 1/3 octave EQ, variable audio delay up to 109 frames (to accommodate the projector), track quality logging, remote control / maintenance via PC Modem and setup or transfer features for easy integration with existing equipment.
Mr. Callahan gave us all an SDDS brochure with detailed system info, and complete specifications. All in all a fascinating insight into specialized pro audio.
by John Fourdraine, Toronto.
Copyright 1996,
Audio Engineering Society Toronto Section Bulletin
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