Chapter 7-Pitch and Timbre
"that attribute of auditory sensation in terms of which sounds may be ordered on a scale extending from high to low" Rossing
---- Pitch is a subjective sensation -----
A Pitch Scale?
Mels. . .this smells
There are 2400 mels between ---> 20 hz and 16,000 Hz
That's 24 barks to all you dogs out there!
Does 1 millibark = 56 decisones or 3.2 megaphones, or what?
I am so confused!
Critical Band ---> (100 mels = 1 bark = 160 Hz)
Remember: What is Sound?
Sound
Sound is what we experience when the ear reacts to a certain range of vibrations. These vibrations themselves can also be called sound. Acoustic instruments generally produce sound when some part of the instrument is either struck, plucked, bowed or blown into. Electronic instruments produce sound indirectly they produce variations in electrical current which are amplified and sent through a speaker.
The three qualities of sound are: pitch, timbre (tone color) and loudness.
Pitch
Pitch is the quality of sound which makes some sounds seem "higher" or "lower" than others. Pitch is determined by the number of vibrations produced during a given time period. The vibration rate of a sound is called its frequency the higher the frequency the higher the pitch. Frequency is often measured in units called Hertz (Hz). If a sound source vibrates at 100 vibrations per second, it has a frequency of 100 Hertz (100 Hz). Mels scale would be found here. The average person can hear sound from about 20 Hz to about 20,000 Hz. The upper frequency limit will drop with age.
The human ear is very adept at filling gaps. There is a body of evidence to show that if the lowest frequency partial is missing from a complex tone, the ear will attempt to fill it in. This effect is used, for instance, by church organists who simulate the effect of say a low ‘C’ for which they do not have a pipe of sufficient size by playing the ‘C’ and ‘G’ an octave above. These two pipes provide all the partials for the lower ‘C’ note except for the lowest frequency, which the ear obligingly provides. Listening to speech or music on a poor quality transistor radio that cannot reproduce low frequencies provides another example. The programme is rendered intelligible by the ear filling in the lowest partial tones. That rapid speech is intelligible suggests that the synthesis in the ear is practically instantaneous.
Timbre
Timbre is a French word that means "tone color". It is pronounced: tam' ber. Timbre is the quality of sound which allows us to distinguish between different sound sources producing sound at the same pitch and loudness. The vibration of sound waves is quite complex; most sounds vibrate at several frequencies simultaneously. The additional frequencies are called overtones or harmonics. The relative strength of these overtones helps determine a sound's timbre.
Dull---Brilliant, Cold----Warm, Pure----Rich
Loudness
Loudness is the amount or level of sound (the amplitude of the sound wave) that we hear. Changes in loudness in music are called dynamics. Sound level is often measured in decibels (dB). Sound pressure level (SPL) is a decibel scale which uses the threshold of hearing as a zero reference point. Sones scale would be found here.
Dynamic Range
The dynamic range of an orchestra can exceed 100dB. If the softest passage is 0db, the loudest passages can exceed 100dB. In electronic equipment the lower limit is the noise level (hissing sound) and the upper limit is reached when distortion occurs. The dynamic range of electronic equipment is also called signal-to-noise ratio.
Thank you:
John McEnary
Associate Professor of Music
Orange Coast College
Tones and semitones. . .cool check it out!
The jnd for pitch has been found to depend on frequency, the sound level, the duration of the tone, and the suddenness of the frequency change.
Figure 7.2 (p. 111) is a good example of how the jnd depends on frequency.
50 Hz ---> the jnd = 3 Hz
150Hz ---> the jnd = 2 Hz
1000 Hz ---> the jnd = 4 Hz
3000 Hz ---> the jnd = 18 Hz
10,000 Hz ---> the jnd = 90 Hz
As Rossing points out in the text, by comparing the Critical Bandwidth and the JND curves, one will discover that the two are different by about 30 JND's! The same mechanism in the ear is responsible for critical bands AND pitch discrimination! The next paragraph is exceedingly interesting. . .
Quiz
1
(in class on Monday, you will be asked to give short
answers to 3 of the following 5 questions)
1) How do mels relate to frequency?
2) What is Sound?
3) How does a bark relate to critical bands?
4) What does the author compare in the last paragraph in section 7.2?
Why?
5) What does PITCH depend upon?
Place
Theory
Helmholtz believed the basilar membrane was a
frequency analyzer, the membrane as a whole can create the effect of
resonances. High frequency near the oval window and Low frequency near
the end of the basilar membrane. (see Bekesy)
What are the problems with Place Theory?
Fine Frequency Discrimination. . .in order
to to respond to rapid changes in frequency, a resonator must have considerable
damping. But damping decreases selectivity (the ability to discriminate
between small differences in frequency). And, why do we hear a complex
tone as one entitiy with a single pitch? (page
118)
Periodicity Theory
The ear performs a time
analysis of the sound wave. The time distribution of electrical impulses
carried by the auditory nerve has encoded into it information about
the time distribution of the sound wave. This information is decoded
by autocorrelation in the central nervous system.
A General Conclusion
None of the current pitch theories is completely successful in explaining
all experiments. Clues
from both frequency and time analysis of the sound are used to determine
pitch.
(in class on Wednesday, you will be asked to give short answers to 3 of the following 5 questions)
1) Why does the author make the comment that Musical performance would be difficult if substantial changes in pitch occurred during changes in dynamic levels? (page 113)
2) What is the 'missing fundamental' phenomena presented in section 7.5?
3) What is the difference between Place Pitch and Periodicity Pitch?
4) Do both these theories have validity? Why?
5) What is the difference between Absolute Pitch and Relative Pitch?
Timbre
An auditory sensation in which two sounds
can be distinguished using any criteria other than pitch, loudness,
or duration. Hmm. . .
Judgment of Timbre must take place under conditions of equal loudness
and pitch.
A multidimensional attribute of sound.
When a object vibrates it propagates sound waves of a certain frequency.
This frequency, in turn, sets in motion frequency waves called harmonics.
The basic frequency and its resultant harmonics determine the timbre
of a sound.
The greater the number of harmonics, the more interesting is the sound
that is produced.
It is an object's ability to vibrate and set up harmonics that determines
the pleasantness of the resultant sound.
Crystal glass sets up harmonics that are more pleasant than ordinary
glass.
The combination of fundamental frequency and its harmonics is a complex
wave form.
(email these questions, you will be asked to give short answers to 3 of the following 3 questions)
1) Why do musical instruments need to be tuned?
2) How does one demonstrate Timbre or tone quality?
3) What is Fourier analysis?
Happy Easter Day!