56
2 The Scientist’s Perspective on Brass Instrument Behaviour
Fig. 2.20 Spectrogram of a descending glissando played on a trombone with the slide in first
position
to the brass instruments and is linked to the ‘brassy’ timbre which characterises
trumpets, trombones and french horns (see Sect. 6.1).
The spectrogram provides an alternative means of displaying the spectral content
of sounds. In this type of display, time is plotted on one axis and frequency on the
other axis; amplitude (or sometimes acoustic power) is shown by a grey or colour
scale. Figure 2.20 illustrates a performance in which a virtuoso trombonist played a
descending glissando over more than five octaves, from C6 to B 1.
The horizontal axis in the spectrogram represents the passage of time during the
glissando. The total time interval of 18 s is divided into time windows short enough
that the signal can be assumed to have a constant repetition frequency during each
window. In each window, the amplitudes of the components in the frequency range
from 0 to 1200 Hz are calculated and represented along the vertical frequency axis
in Fig. 2.20 using a colour scale.
A red line descending from the upper left of the spectrogram shows how the
fundamental frequency f R of the signal drops during the glissando. Starting at just
over 1000 Hz, f R falls continuously until around 850 Hz, since in this frequency
region, there are no significant resonances in the instrument and there is therefore no
feedback to the lips. Below 850 Hz (a pitch between G 5 and A5), f R falls in a series
of steps: the almost horizontal part of each step corresponds to the frequency of an
2 The Scientist’s Perspective on Brass Instrument Behaviour
Fig. 2.20 Spectrogram of a descending glissando played on a trombone with the slide in first
position
to the brass instruments and is linked to the ‘brassy’ timbre which characterises
trumpets, trombones and french horns (see Sect. 6.1).
The spectrogram provides an alternative means of displaying the spectral content
of sounds. In this type of display, time is plotted on one axis and frequency on the
other axis; amplitude (or sometimes acoustic power) is shown by a grey or colour
scale. Figure 2.20 illustrates a performance in which a virtuoso trombonist played a
descending glissando over more than five octaves, from C6 to B 1.
The horizontal axis in the spectrogram represents the passage of time during the
glissando. The total time interval of 18 s is divided into time windows short enough
that the signal can be assumed to have a constant repetition frequency during each
window. In each window, the amplitudes of the components in the frequency range
from 0 to 1200 Hz are calculated and represented along the vertical frequency axis
in Fig. 2.20 using a colour scale.
A red line descending from the upper left of the spectrogram shows how the
fundamental frequency f R of the signal drops during the glissando. Starting at just
over 1000 Hz, f R falls continuously until around 850 Hz, since in this frequency
region, there are no significant resonances in the instrument and there is therefore no
feedback to the lips. Below 850 Hz (a pitch between G 5 and A5), f R falls in a series
of steps: the almost horizontal part of each step corresponds to the frequency of an