Music Performed at Home
by James Adrian
Most people hear music from recordings that
reproduce sounds created by performers - sounds created elsewhere. What if you could have the music played in your home? What if the music coming
out of some machine was produced
rather than reproduced
Reproduction, beginning with two speaker stereo and
culminating in surround sound, has left us with an artificial experience. When you come home and hear a quartette playing music in the next room, you might
ask "Who has come to visit?" When you hear the stereo playing, you could have no such question. The auditory processing of the brain is very sophisticated.
For all of the many decades of trying, the human ear is not fooled by any known means of reproduction. Just to mention one small issue, the size and shape of
your living room does not produce the acoustics of a band playing on a stage.
Besides the acoustics, there are other glaring differences
between production and reproduction. When more than one instrument is conveyed through a loudspeaker, the instruments interact. Intermodulation and
frequency modulation between the instruments within the speaker produces artificial sound components that have never been completely eliminated by the
technology of reproduction. These sound components are extraneous, artificial and detectable.
There is another type of distortion that is produced by
speakers, but this one can be dealt with perfectly. When a single tone is produced by an instrument, it produces the consciously heard pitch together with many
others that each have a frequency that is an integer multiple of the pitch that we consciously hear. These are called overtones
. The relative loudness of
these overtones accounts for the tone quality difference between different natural sounds. A speaker that is not perfectly unbiased in its conveyance of these
overtones will not produce an unnatural sound, but it will produce a slightly altered tone. Fortunately, any given speaker does this to a consistent extent and in a
consistent way. It therefore can be corrected. If a specific speaker is used to play the sound of a specific instrument, the series of overtones can be adjusted by
computations made beforehand by the computer that creates the data that is to drive the speaker.
This means that any single musical line can be
flawlessly in a place of your choosing by a computer driving one or more speakers, resonators or diaphragms. So long as each transducer
produces only one musical line, it is a live production and not a reproduction. The acoustics are those of the room where the music is being performed. There
is no intermodulation distortion. There is no frequency modulation distortion. The voice line is customized for the size and type of speaker assigned to that voice.
One might wonder why the interactions between overtones
does not produce distortions that cannot be corrected. It is because whenever the overtones are exact integer multiples of the lowest pitch (this is the one we hear),
the movement of the vibrating body (the speaker in this case) repeats a cycle of movement over and over again exactly. Any such movement is mathematically
identical to some
sound that has integer multiple overtones, despite the source of the distortion. Because the relative amplitude of overtones can be
adjusted, the distortion is eliminated.
The system is especially valuable in the case of compositions that are either very difficult or impossible to play manually. Music schools might also value it for the teaching of composition.
If such a system were made today, the physical media used
to distribute performances would probably be DVD's, but the data format and frequency range specifications would need to be decided by the copyright holder.
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