Sound, Hearing, and the Brain
May 1, 2018
Spoiler Alert – this one is a bit dense and philosophical.
How do sound qualities arise? And how do we hear music as pitch, tone color, harmony, and melody, when nothing like these things actually exist in nature?
Sound waves go through cycles, often countless times per second. During each cycle the “amplitude” (the wave height) changes from one instant to instant. The number of cycles per second correlates with the ‘pitch’ that we hear. But in this conscious phenomenon there is no awareness at all of the loudness changing from instant to instant. As long as the frequency of the wave holds constant, the sound that we hear prolongs itself constantly through duration in time.
Thus, perceiving a steady pitch at a steady loudness is due to something that in terms of what is going on physically in nature is quite discontinuous. When the piano plays a Middle C, we do not hear a series of 261 sudden increases in loudness each second. Nor do we hear 440 sudden increases in loudness when the oboe plays its A above middle C to tune the orchestra. Something discontinuous, fitful and periodic in nature ends up as something continuous and steady in consciousness. Only when the vibration rate drops below around 20 cycles per second do we begin to hear the separate puffs of air, but at the price that we no longer hear a pitch.
What if our consciousness could run at a ‘tempo’ that allowed us to hear these individual peaks in loudness? Seconds would seem to take minutes, and small fractions of seconds would seem like seconds. The result is that the very nature of what we would ‘hear’ would be totally different: discontinuity in time would replace continuity.
This would be the equivalent in time of putting a specimen under a microscope and magnifying it in space. The greater the magnification, the less the specimen looks as it did to the unaided eye. If we were not told that it was the same object in both cases, we would be hard put to realize its identity.
Pitch, the basic substrate of all our musical perception, would disappear, and be replaced with an effect somewhat like a ratchet, or a rapid series of metronome clicks with silence between successive clicks. Gone would be the very building blocks out of which musical structure is created.
Sound: Instrumental Tone Quality versus a Chord of Pitches
Our experience of instrumental tone color (a clarinet’s sound versus a violin’s sound or versus the sound of a human voice) is, as with pitch, based on a fortunate illusion, a simplification and then recasting of sensations reaching our brain.
When an instrument, like a clarinet, plays what we perceive as a single pitch, a scientific examination of its wave form reveals something that resembles more a ‘chord’ of many pitches than what gives us the perception of a single pitch.
There is no ‘reason’ why, we might hear simply one chord versus another in the different instruments, minus any change in instrumental quality. After all, chords are part of the normal conscious phenomena that we perceive about sound. Why do we need something extra when we might content ourselves with just perceiving chords?
When we perceive what we term a chord, most often the various individual pitches in the chord are sounding with approximately the same loudness. What if the different pitches in a chord all had different loudnesses. This would add a serious level of complication. It is this extra layer of complication that the brain “simplifies” for us. What we hear is not different loudnesses among the different pitches in otherwise similar chords, but simply a different tone quality, or timbre, to the overall sound. A French horn and a violin playing Middle C produce the same chord of pitches, but the relative loudness of one pitch to another is different. How impoverished would our perception of sound be if it was bereft of this extra
parameter of tone quality. Sound would “sound” like shades of grey without any other color.
Part of the ‘illusion’ of tone quality is that we hear one pitch instead of many, and our brain casts the lowest pitch in the chord as the pitch we associate with the note, and as for the rest of the notes in the chord, depending on their mutual loudness, the brain recasts the phenomenon of pitch as the phenomenon of tone quality.
What if our brain had the ability to resolve the single sound of an instrument, at a single pitch, into a chord of many different pitches? The answer is simple. Gone would be melody and gone would be harmony.
Conclusion number two: This almost deceitful sleight of hand by the brain allows for the richness of musical structure.
P.S. Two other parameters of musical sounds, rhythm and duration, do not depend on sound to be perceivable. Duration is simply the inner experience of time in consciousness, and needs nothing external to
mark its progress. And rhythm, which in a way depends on duration, can be taught to a deaf person through a sense other than hearing: touch, for instance.
P.P.S. Of all the arts, music comes closest to being the simple conscious perception of time.