(prior page: Pitch and Inflection)
Now that we’ve learned what pitch and inflection are, it’s time to see how they influence the tone quality of whistled sounds. The first aspect of tone quality we will be dealing with is musicality, which can be loosely defined as the extent to which a sound’s pitch can be determined by human ears. The first factor determining musicality is sharpness of inflection.
The song of the Field Sparrow is famous for its acceleration. Many people describe it as a musical “bouncing-ball” trill. The acceleration is obvious on the spectrogram, as the elements towards the end of the song are much more closely spaced than the elements towards the beginning:
Compare the song of the Field Sparrow with the song of its relative the Black-chinned Sparrow, also a “bouncing-ball” singer:
A quick review: First, compare these songs based on your knowledge of pitch and inflection. You’ll notice that this particular Field Sparrow song lacks the two introductory whistles in the Black-chinned Sparrow songtype. Also, while this Field Sparrow song consists of a series of downslurred whistles, this Black-chinned Sparrow song contains a series of upslurred whistles. (I’m careful to say “this song” because the songs of both species, like those of the Canyon Wren, are quite variable.) Both series accelerate, and both rise just slightly in pitch. Got it? Now on to tone quality.
Listen carefully to both songs and notice how different they sound. The Field Sparrow’s song has a musical tone quality throughout, while the Black-chinned Sparrow’s song starts out musical but becomes decidedly unmusical by the end of the song: the last few notes are basically just a toneless rattle. You are hearing differences in the musicality of these notes caused by differences in the extent and sharpness of their inflection. Basically, the more vertical the line on the spectrogram, the less musical the note. An entirely vertical line on the spectrogram would sound like a pop or a click. As the notes of the Black-chinned Sparrow’s song become more and more vertical (that is, more sharply inflected), they begin to sound less like whistles and more like clicks — which is to say, less musical.
The Field Sparrow’s notes remain much more musical, even at the end of its song, in part because its notes remain decidedly slanted throughout. Notice that they sweep across a much smaller range of frequencies than the notes of the Black-chinned Sparrow. Trying to get from a very low frequency to a very high one in a very short time is a recipe for a vertical line on the spectrogram (and thus an unmusical note).
Here’s an example of a whistle so nearly vertical that it doesn’t sound musical at all:
These California Quail calls may look like vertical lines on the spectrogram, but they’re really extremely sharply upslurred whistles. This is why the notes sound slightly different from a click or a pop: there’s a mild “flicking” quality to them.
Effects of Pitch on Tone Quality
Besides the sharpness of inflection, the other major factor affecting the tone quality of whistles is pitch. Very low-pitched whistles (below 1 kHz), like the songs of many doves and owls, have a “hooting” or “cooing” quality:
Slightly higher-pitched whistles, meanwhile, have a mellow quality, as do the notes of this Northern Saw-whet Owl:
Once you get up into the 3-5 kHz range, whistles with a similar shape on the spectrogram will begin to sound much thinner, as does the song of this Mountain Chickadee:
Above about 6 kHz, whistles start to sound decidedly less musical, and it becomes very difficult to discern their pitch. They start to sound sibilant, like the sound of the letter “s” in English, but in fact they are spectrographically very different from that sound; the similarity is a trick of our ears. I use the word high-sibilant to distinguish these sounds from sounds that are truly sibilant, which are sounds that contain lots of noise at high frequencies.
The “seer” alarm call of the American Robin is a good example of a high-sibilant sound:
(next page: noise)