THE MASSING OF OVERTONES IN SOUND REPRODUCTION
© 1983 The Anstendig Institute
A supplement to be read with The Anstendig Institute's paper "EQUALIZATION"
ALL TONES ARE COMPOSITES OF THE FUNDAMENTAL TONE PLUS OTHER TONES
All tones when produced excite other, different tones that vibrate along with them. These other tones consist mostly of sounds called overtones that are above the pitch of the tone that was produced, but also include less apparent sounds, which are called undertones, that are below the original pitch. Every sound consists of the actual sound that is produced, called the fundamental, as well as the overtones and undertones; to a large degree, the number of overtones and undertones and their loudness, relative to the fundamental, determines the character of a sound. (There are other, more difficult to define factors that also determine the character of a sound, such as intensity, vibrato, quality of attack, etc.) Even so called pure tones have some overtone structure. These overtones and undertones are generally referred to as harmonics because they follow certain precise harmonic laws in their structure.
IT IS A SIMPLE FACT OF PHYSICS THAT, NO MATTER HOW IT IS PRODUCED, ANY SOUND EXCITES OTHER SOUNDS TO VIBRATE WITH IT.
Those other sounds, the harmonics, may be louder or softer in volume or greater or lesser in quantity, but they are there.
ALL RECORDED SOUNDS BECOME FUNDAMENTALS, PRODUCING THEIR OWN HARMONICS DURING PLAYBACK
When sounds are recorded and played back, all the sounds that emanate from the loudspeaker become fundamentals, even those that are the overtones and undertones of fundamentals in the sounds that were recorded. This means that they all produce their own set of harmonics, just like any live fundamental tone. The result is a massing of these over/undertones similar to, but not the same as, doubling them.
THE ADDITIONAL HARMONICS IN ALL SOUND REPRODUCTION DISTORT THE ORIGINAL
The harmonics that are added by the playback process blur the sound textures, especially within the general range of the fundamental notes, and add shrillness by emphasizing the high frequencies.
Unfortunately, the harmonic structures of most voices and musical instruments peak in the same frequency range to which our ear is most sensitive. This adds an additional, crucial distortion to those listed in the paper "Equalization" as reasons why sound reproduction has to be equalized.
IN RELATION TO ACOUSTICS, THE ANSTENDIG INSTITUTE IS CONVINCED THAT IMITATION OF THIS DISTORTED EMPHASIS OF THE STRUCTURE OF THE HARMONICS IN SOUND REPRODUCTION IS A MAJOR FACTOR IN THE DESIGN OF FAULTY CONCERT HALLS, HALLS THAT PRODUCE A SOUND VERY MUCH LIKE THE DISTORTIONS OF SOUND REPRODUCTION (see our papers "Equalization Addendum" and "Acoustics”).
For the technically minded, this neglected fact became apparent during The Anstendig Institute's investigation of discrepancies between the frequency curves resulting from our equalization of recordings and the equalization curves arrived at by Fletcher and Munson. Allowing for the fact that the Fletcher-Munson curves are an average that represents a mean-sensitivity of hearing among many people, our curves differed strongly from theirs in two respects: they demanded greater amounts of compensation and they differed subtly in the frequencies upon which the compensation centered. Careful spectral analysis showed that our curves peaked slightly lower, at approximately 27,OOOHz (25,000Hz to 33,000Hz) than those of Fletcher and Munson. These frequencies correspond to the frequencies at which the harmonics of various musical instruments and the human voice peak and are explained by the additional overtones produced by the recorded sounds during playback.
The Anstendig Institute is a non-profit, tax-exempt, research institute that was founded to investigate the vibrational influences in our lives and to pursue research in the fields of sight and sound; to provide material designed to help the public become aware of and understand vibrational influences; to instruct the public in how to improve the quality of those influences in their lives; and to provide the research and explanations that are necessary for an understanding of how we see and hear.