Acoustics is the science of sound. It is the study of sound propagation, transmission, reverberation, echo phenomenona... Acoustics applies to the fields of construction, transport, medical and electronics, and also to music! The science of musical instruments is called musical acoustics.
A few details about musical acoustics
This subject, where wave physics and music meet, finds its roots in classical times particularly with the work of Pythagoras, who already established links between the length of a rope and the sound pitch produced by this rope. (Check out the science behind a sound). Today, scientific knowledge and tools have evolved so that we are able to simulate and create models of physical phenomenons (air flow, vibration modes, acoustic input impedance ...) inside instruments.
Research in musical acoustics allows us to understand and improve musical instruments by studying their vibratory properties, their radiation as well as the relationship between the musician and instrument. The instruments are modelled thanks to acoustic simulation software (Read Syos Jobs : Simulation Engineer) and based on experiments on real instruments.
Parameters studied in musical acoustics
To characterize a sound signal, acoustics uses four main quantities: the duration of the sample, its pitch, its intensity (amplitude) and its timbre. Knowing these parameters provides a better understanding of an instrument, and also ways to synthesize it by recomposing a signal of its own.
Duration, pitch and amplitude are quantifiable values, they have units. They are characterized respectively by:
- the second (s)
- the Hertz (Hz)
- the decibel (dB)
However, timbre is not quantifiable and has no unit. Timbre is defined by the harmonic composition of the sound and its attack (the beginning of the sound signal). In acoustics, timbre is expressed with statistical notions (Spectral Density of Power). For a musician, it is with words such as bright, clear, dark, warm... that timbre is best defined (and this is where psycho-acoustics as a science of auditory perception comes in !)
Example: experiment on the saxophone
Here, we blew in our saxophone, playing an A (440 Hz), which corresponds to a F# with on alto saxophone. Have a listen!
In the figures below, we observe the pitch and duration (on the spectrogram) and the amplitude and duration (on the time signal). But where is the timbre? As said before: it is impossible to quantify, so it's impossible to represent on a graph.
The time signal is shown in blue above. This is exactly what the microphone picks up when a saxophone is played. We can distinguish three parts:
- the beginning transient (1)
- the stationary regime (2)
- the end transient (3)
These are the main steps for any wind instrument. However, the transients and harmonic composition are specific to each instrument, the trumpet attack is often much drier than the saxophone for example. This is one of their differences in tone …
The spectrogram is a graph that gives us the pitch (the frequency) as a function of time (the duration of the signal). On this spectrogram, it is clear that the note is maintained for about one second. The spectrogram also shows us which notes are played. We clearly see the fundamental note (440 Hz) and the harmonics. We are reassured, we played the fundamental note well, a 440!
Here, we also see that the saxophone is harmonic: each frequency played is a multiple of the fundamental!
The harmonics observed are specific to the saxophone, they define its timbre. The mouthpiece of your saxophone is the centrepiece to adding (or maybe not) harmonics to your sound: take a look at this article on what the influence of the mouthpiece chamber on the tone is !
Little summary :
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The vocabulary of musical acoustics mainly consists of: the duration, the pitch, the amplitude, and the timbre.
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Duration, pitch and amplitude are quantifiable.
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The tone is expressed statistically, but particularly with your words.
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The spectrogram allows you to analyze your sound and know its harmonic composition.
Curious to put into words the timbre of your saxophone? Come and test the variety of Syos Mouthpieces!
