Ladefoged – Chapter 2

[Simon]

Loudness and pitch

[blue fish]

In chapter 2, page 18 of the Peter Ladefoged reading it says:

“There is, however, one point to be careful about: in order to build up larger variation in air pressure, the particles move farther and more rapidly. But this does not mean the peaks of pressure occur more frequently. As you can see in figure 2.1, although one sound has twice the amplitude of the other, the peaks of pressure in both of them are still occurring at the same rate of one every one-hundredth of a second. One of the two tuning forks may be making larger vibrations than the other, but they are both making the same number of complete vibrations pet second.”

I can’t get my head around why a bigger change in air pressure would not have more cycles. There is an example that follows, that tries to explain this but it doesn’t clear it up for me.

[Simon]

Ladefoged’s point is simple, but maybe his explanation is not. He is saying that the amplitude of a sound and its frequency are independent properties. We can change one, without changing the other.

Let’s see if another example makes it clearer. Let’s pick a nice simple source of sound – a violin string.

A violin player can independently control the note being played (i.e., the frequency) and how loud that note is (i.e., the amplitude).

Now, given that a player can independently control these, and that a listener will perceive them, then the physical signal that is transmitted through the air must have two separate physical properties: one that corresponds to the note’s frequency and another that corresponds to its amplitude.

The physical manifestation of amplitude is the amount by which air particles move back-and-forth. The physical manifestation of frequency is how many times per second they move back-and-forth.

Changing the frequency is shown in Ladefoged’s Fig. 2.3. Changing the amplitude is in Fig. 2.1.

(The perceptual correlate of amplitude is loudness. The perceptual correlate of frequency is pitch. In both cases, the relationship between the physical property and the percept is non-linear.)

[Author]

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