ComposerTech Spectrum #1

Day 208 Week 29 Q3 Friday, July 28, 2023

Spectrum refers to a range of frequencies, the physics variable most connected to pitch.

After the range from loud to soft, which falls under the umbrella of dynamics, arguably the next most important attribute of sound for composers is the spectrum. Almost every sound system has a volume control to address loudness and softness. Most musical instruments have the ability to control how loud or softly they can be played. This is what made the piano, whose full name is pianoforte, such a big deal enabling it to blow by the harpsichord and never look back. 

Almost every sound system or process also has a tone control to control the contribution of lows and highs. In a different manner, this is another reason the pianoforte came to dominate; the range from low to high notes is greater than anything except for the organ, which was invented two thousand years earlier, in 300 BC.

Now all musicians understand the concept of pitch, which is a psychological, perceptual variable, that repeats every octave. One octave change refers to a doubling or halving of frequency and is perceived as the same pitch. The physical concept of frequency refers to the number of vibrations per second a sound changes, and it is a physical variable. We have all heard of A 440, which continues to function as the dominant pitch reference globally.  The reference note, A has a frequency of 440 vibrations per second or 440 cps (cycles per second), which is more often expressed as 440 Hz. One hertz means “one event per second” (where the event being counted may be a complete cycle) and is named after Heinrich Hertz in the 1890s.

The range of notes a human can hear is called a spectrum where the lowest note we can discern is 20 Hz and the highest is 20,000 Hz. This range of frequencies is 1000 to 1 or roughly ten octaves, whereas the range from loud to soft is 1 million to 1. We are not equally sensitive to all frequencies. The frequencies where speech occurs are where we are the most sensitive, as these impact intelligibility.  

Also, in terms of frequency, the energy in the universe is widely regarded as inversely proportional to frequency. This means low-frequency sounds have more energy than high-frequency sounds. A simple tone control affects the relative contribution of low and high frequencies. Other controls can break up the spectrum into thousands of slices where the relative contribution can be managed. 

Composers make powerful use of how energy is distributed across the audio spectrum, which has a tremendous emotional impact.